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Kinematic constraints on the Rodinia-Gondwana transition
... The breakup of the supercontinent Rodinia, and subsequent formation of Gondwana, coincided with critical Earth system changes that led to the Phanerozoic world of extensive macroscopic mineralised life, significantly oxygenated atmosphere and hydrosphere, and a buffered climate devoid of whole-planet glaciations [1][2][3]. Determining any interdependence between these phenomena, e.g., [1,[4][5][6], requires constructing full-plate tectonic reconstructions of the globe [7,8], which necessitate a fundamental understanding of the temporal link between tectonically controlled geological features (such as rift basins) and plate tectonic phenomena (such as continental plate sundering and ocean crust formation [8,9]). ...
... The breakup of the supercontinent Rodinia, and subsequent formation of Gondwana, coincided with critical Earth system changes that led to the Phanerozoic world of extensive macroscopic mineralised life, significantly oxygenated atmosphere and hydrosphere, and a buffered climate devoid of whole-planet glaciations [1][2][3]. Determining any interdependence between these phenomena, e.g., [1,[4][5][6], requires constructing full-plate tectonic reconstructions of the globe [7,8], which necessitate a fundamental understanding of the temporal link between tectonically controlled geological features (such as rift basins) and plate tectonic phenomena (such as continental plate sundering and ocean crust formation [8,9]). ...
... Neoproterozoic mafic volcanics of the Coompana Province c. 860 Ma may also be part of the Willouran LIP [52]. The Willouran LIP (Figure 2) is interpreted to represent the first major phase of rifting within the Adelaide Superbasin, and thus the initiation of Rodinia breakup at the eastern margin of Proterozoic Australia that led to the development of the proto-Pacific Ocean [8]. Presently, the only exposures of complete sections of the Arkaroola Subgroup ( Figure 3) are located in the Arkaroola/Mount Painter area, and the Davenport and Denison Ranges (Peake and Denison Inliers) (Supplementary Figure S1). ...
Continental rifts have a significant role in supercontinent breakup and the development of sedimentary basins. The Australian Adelaide Superbasin is one of the largest and best-preserved rift systems that initiated during the breakup of Rodinia, yet substantial challenges still hinder our understanding of its early evolution and place within the Rodinian supercontinent. In the past decade, our understanding of rift and passive margin development, mantle plumes and their role in tectonics, geodynamics of supercontinent breakup, and sequence stratigraphy in tectonic settings has advanced significantly. However, literature on the early evolution of the Adelaide Superbasin has not been updated to reflect these advancements. Using new detrital zircon age data for provenance, combined with existing literature, we examine the earliest tectonic evolution of the Adelaide Superbasin in the context of our modern understanding of rift system development. A new maximum depositional age of 893 ± 9 Ma from the lowermost stratigraphic unit provides a revised limit on the initiation of sedimentation and rifting within the basin. Our model suggests that the basin evolved through an initial pulse of extension exploiting pre-existing crustal weakness to form half-grabens. Tectonic quiescence and stable subsidence followed, with deposition of a sourceward-shifting facies tract. Emplacement and extrusion of the Willouran Large Igneous Province occurred at c. 830 Ma, initiating a new phase of rifting. This rift renewal led to widespread extension and subsidence with the deposition of the Curdimurka Subgroup, which constitutes the main cyclic rift sequence in the Adelaide Superbasin. Our model suggests that the Adelaide Superbasin formed through rift propagation to an apparent triple junction, rather than apical extension outward from this point. In addition, we provide evidence suggesting a late Mesoproterozoic zircon source to the east of the basin, and show that the lowermost stratigraphy of the Centralian Superbasin, which is thought to be deposited coevally, had different primary detrital sources.
... The breakup of the supercontinent Rodinia, and subsequent formation of Gondwana, coincided with critical Earth system changes that led to the Phanerozoic world of extensive macroscopic mineralised life, significantly oxygenated atmosphere and hydrosphere, and a buffered climate devoid of whole-planet glaciations [1][2][3]. Determining any interdependence between these phenomena, e.g., [1,[4][5][6], requires constructing full-plate tectonic reconstructions of the globe [7,8], which necessitate a fundamental understanding of the temporal link between tectonically controlled geological features (such as rift basins) and plate tectonic phenomena (such as continental plate sundering and ocean crust formation [8,9]). ...
... The breakup of the supercontinent Rodinia, and subsequent formation of Gondwana, coincided with critical Earth system changes that led to the Phanerozoic world of extensive macroscopic mineralised life, significantly oxygenated atmosphere and hydrosphere, and a buffered climate devoid of whole-planet glaciations [1][2][3]. Determining any interdependence between these phenomena, e.g., [1,[4][5][6], requires constructing full-plate tectonic reconstructions of the globe [7,8], which necessitate a fundamental understanding of the temporal link between tectonically controlled geological features (such as rift basins) and plate tectonic phenomena (such as continental plate sundering and ocean crust formation [8,9]). ...
... Neoproterozoic mafic volcanics of the Coompana Province c. 860 Ma may also be part of the Willouran LIP [52]. The Willouran LIP (Figure 2) is interpreted to represent the first major phase of rifting within the Adelaide Superbasin, and thus the initiation of Rodinia breakup at the eastern margin of Proterozoic Australia that led to the development of the proto-Pacific Ocean [8]. Presently, the only exposures of complete sections of the Arkaroola Subgroup ( Figure 3) are located in the Arkaroola/Mount Painter area, and the Davenport and Denison Ranges (Peake and Denison Inliers) (Supplementary Figure S1). ...
Continental rifts have a significant role in supercontinent breakup, and the development of sedimentary basins. The Australian Adelaide Superbasin is one of the largest and best-preserved rift systems that initiated during the breakup of Rodinia, yet substantial challenges still hinder our understanding of its early evolution and place within the Rodinian supercontinent. In the past decade, our understanding of rift and passive margin development, mantle plumes and their role in tectonics, geodynamics of supercontinent breakup, and sequence stratigraphy in tectonic settings has advanced significantly, however literature on the early evolution of the Adelaide Superbasin has not been updated to reflect these advancements. Using new detrital zircon age data for provenance, combined with existing literature, we examine the earliest tectonic evolution of the Adelaide Superbasin in the context of our modern understanding of rift system development. A new maximum depositional age of 893 ± 9 Ma from the lowermost stratigraphic unit provides a revised limit on the initiation of sedimentation and rifting within the basin. Our model suggests that the basin evolved through an initial pulse of extension exploiting pre-existing crustal weakness to form half-grabens. Tectonic quiescence and stable subsidence followed, with deposition of a sourceward-shifting facies tract. Emplacement and extrusion of the Willouran Large Igneous Province occurred at c. 830 Ma initiating a new phase of rifting. This rift renewal led to widespread extension and subsidence with deposition of the Curdimurka Subgroup, which constitutes the main cyclic rift sequence in the Adelaide Superbasin. Our model suggests that the Adelaide Superbasin formed through rift propagation an apparent triple junction, rather than apical extension outwards from this point. Additionally, we provide evidence suggesting a late Mesoproterozoic zircon source to the east of the basin, and show that the lowermost stratigraphy of the Centralian Superbasin, which is thought to be deposited coevally, had different primary detrital sources.
... Ga (Li et al., 2008) and East Gondwana at 0.6-0.5 Ga (Meert, 2003). Convergence of circum-Antarctic continents to form Gondwana (Meert, 2003;Boger, 2011;Merdith et al., 2017) resulted in the formation of several major crustal scale suture zones, such as the East African orogen (660-610 Ma, Stern, 1994), the Mozambique orogen (580-550 Ma, Jacobs et al., 2003), the Damara orogen (550-520 Ma, Boger, 2011) and the 530-490 Ma Kuunga orogen (Meert et al., 1995;Boger, 2011). ...
... It is, however, agreed that the 0.95-0.90 Ga tectonothermal event probably resulted in the formation of Enderbia as a part of Rodinia (Dasgupta et al., 2017;Merdith et al., 2017). Dobmeier and Raith, 2003) and adapted from Sarkar and Schenk (2014). ...
... In the study area, geochronological data (Biswal et al., 2007;Simmat and Raith, 2008;Chatterjee et al., 2017a;Chatterjee et al., 2017b;Ranjan et al., 2018) clearly establish that the last tectonothermal episode recorded by the Bastar craton and EGP rocks in the TBSZ (~0.5 Ga) is broadly coeval with the Kuunga orogeny Boger, 2011;Merdith et al., 2017), which resulted due to the collision of the Australo-Antarctic Block and the Indo-Antarctic Block in East Gondwana (Fig. 8a). The effect is certainly more intense at the Bastar craton -EGP contact (Fig. 8b), and records of the Tonian age orogeny, which is primarily responsible for granulite facies metamorphism in the EGP, are nearly obliterated (the only exceptions are a few monazite U-Pb data given by Simmat and Raith, 2008). ...
Nd model ages show that the suture between the Archean Bastar craton and Proterozoic Eastern Ghats Province (a part of the Eastern Ghats Belt), India is marked by a broad shear zone that contains a mixture of rocks from both the blocks. In this suture zone, amphibolite facies rocks of the Bastar craton were subjected to high pressure granulite facies metamorphism possibly at ~500 Ma (published isotopic data). New petrological, geothermobarometric and P-T pseudosection studies show that dehydration-melting of amphibole (in mafic protolith) and of biotite (in quartzofeldspathic protolith) along a clockwise P-T path led to peak metamorphic conditions of 9.75 ± 0.5 kbar; 875 ± 30 °C. Mafic granulites from the Eastern Ghats Province had an earlier metamorphic history of isobaric cooling from unknown peak metamorphic conditions, but currently record P-T maximum values of 9.25 ± 0.25 kbar; 825 ± 25 °C. Followed by cooling through ~100 °C from the peak metamorphic conditions, mafic granulites from the Bastar craton were exhumed to mid-crustal levels by decompression-cooling, probably as a tectonic wedge. This decompression-cooling is also shared by charnockitic rocks of the Bastar craton and mafic granulites of the Eastern Ghats Province. We interpret further burial of the Bastar craton rocks as a result of underthrusting beneath the Eastern Ghats Province, consistent with available seismic data. Total absence of any evidence of ocean opening or closure between the Bastar craton and the Eastern Ghats Province at around 500 Ma, coupled with interpretation of deduced P-T paths, suggest the shear zone resulted from far-field stress related to the Kuunga orogeny in an intraplate setting. This would support a model of Tonian age amalgamation of the Bastar craton and the Eastern Ghats Province as a part of the Greater Indian Landmass.
... Others (e.g. Merdith et al., 2017aMerdith et al., , 2017bCollins and Pisarevsky, 2005;Dobmeier et al., 2006) consider India not to have been part of Rodinia at all, but an independent entity located at mid-latitudes around 770 Ma, which subsequently collided with the Congo craton along the East African Orogen around 540 Ma during the formation of Gondwana (e.g. Clark et al., 2020). ...
... Li et al., 2008), although a few studies prefer the breakup to have been earlier (e.g. Merdith et al., 2017aMerdith et al., , 2017b). An important implication of this interpretation is that the EGP (along with the Rayner Province) preserves evidence of the breakup, and must therefore have been an integral part of Rodinia. ...
... The first possibility is compatible with Rodinia-Gondwana transition models that suggests that cratonic India was indeed not a part of Rodinia, and only collided with EGP-Rayner during Gondwana amalgamation (e.g. Collins and Pisarevsky, 2005;Merdith et al., 2017b). This would imply that the EGP-Bastar/Rengali Province contact must have been a Neoproterozoic suture modified by subsequent intracrustal shortening (e.g. ...
The Eastern Ghats Province (EGP) of India is considered to have been a part of the supercontinents Rodinia and Gondwana at c. 1.0 Ga and 500 Ma, respectively. A range of ages spanning much of the Neoproterozoic have been periodically reported from parts of the EGP, indicating that the terrane remained tectonically active in the interval between Rodinia and Gondwana amalgamation, although the nature of the associated events remains uncertain. In this study conducted on the northern EGP, we constrain these enigmatic events from structural (field, microstructural and Electron Backscatter Diffraction studies), metamorphic (pseudosection modelling and geothermobarometry) and geochronological (monazite chemical dating) evidence. The area is multiply deformed, with the D 1 and D 2 shortening deformation accompanying granulite facies metamorphism that peaked at temperatures in excess of 900 • C, at ~955 ± 28 Ma. Following hydrous fluid infiltration at ~808 ± 10 Ma, the entire northern EGP was affected by an extensional deformation event D 3 that reoriented all earlier fabrics into an E-W trending, northerly dipping orientation. Deformation microstructures and results of geothermobarometry indicate that D 3 operated at around 600 • C at ~711 ± 18 Ma. Dextral strike-slip deformation (D 4) along the Mahanadi Shear Zone operated under greenschist facies conditions and did not reset monazite isotope system-atics in the region. The signature of mid-crustal extension during D 3 is likely to be associated with the break-up of Rodinia. The lack of corresponding evidence for mid-Neoproterozoic extension in the adjacent Indian cratons suggests relative uplift of the EGP following Gondwana amalgamation.
... changes of continentocean boundaries (COBs)), in pre-Gondwana times it is difficult to be more precise than matching the margins of large continents and for smaller cratons and terranes it is almost impossible. A pertinent example of this are the four different proposed configurations of Australia and Laurentia during Rodinia (see reviews by Li et al., 2008;Merdith et al., 2017b), which all broadly match the same margins against each other (east coast of Australia with the west coast Laurentia, with or without an intervening continent) but place them in different relative positions. ...
... Similarly, models requiring an implausible kinematic evolution in order to meet present-day configurations cannot be correct. A tangible example is Rodinia, for which a range of configurations could be permissible based on available palaeomagnetic and geological data (see reviews in Evans, 2013;Li et al., 2008;Merdith et al., 2017b). However, analysing the sequence of plate motions required to translate each continent to their (better constrained) positions during the Palaeozoic is more plausible in some of these scenarios than others, such as not requiring individual terranes or blocks to cross multiple ocean basins or navigate their way around a stable continent (Merdith et al., 2017b). ...
... A tangible example is Rodinia, for which a range of configurations could be permissible based on available palaeomagnetic and geological data (see reviews in Evans, 2013;Li et al., 2008;Merdith et al., 2017b). However, analysing the sequence of plate motions required to translate each continent to their (better constrained) positions during the Palaeozoic is more plausible in some of these scenarios than others, such as not requiring individual terranes or blocks to cross multiple ocean basins or navigate their way around a stable continent (Merdith et al., 2017b). Further examples where kinematic constraints add useful insights are when constructing models that explicitly trace the evolution of plate boundaries and tectonic plates. ...
Recent progress in plate tectonic reconstructions has seen models move beyond the classical idea of continental drift by attempting to reconstruct the full evolving configuration of tectonic plates and plate boundaries. A particular problem for the Neoproterozoic and Cambrian is that many existing interpretations of geological and palaeomagnetic data have remained disconnected from younger, better-constrained periods in Earth history. An important test of deep time reconstructions is therefore to demonstrate the continuous kinematic viability of tectonic motions across multiple supercontinent cycles. We present, for the first time, a continuous full-plate model spanning 1 Ga to the present-day, that includes a revised and improved model for the Neoproterozoic–Cambrian (1000–520 Ma) that connects with models of the Phanerozoic, thereby opening up pre-Gondwana times for quantitative analysis and further regional refinements. In this contribution, we first summarise methodological approaches to full-plate modelling and review the existing full-plate models in order to select appropriate models that produce a single continuous model. Our model is presented in a palaeomagnetic reference frame, with a newly-derived apparent polar wander path for Gondwana from 540 to 320 Ma, and a global apparent polar wander path from 320 to 0 Ma. We stress, though while we have used palaeomagnetic data when available, the model is also geologically constrained, based on preserved data from past-plate boundaries. This study is intended as a first step in the direction of a detailed and self-consistent tectonic reconstruction for the last billion years of Earth history, and our model files are released to facilitate community development.
... Several adaptations to the model have been proposed (Li et al., 2008(Li et al., , 2013Li and Evans, 2011) and more recently, the Tarim Block has been proposed as an alternative Missing Link between Australia and Laurentia (Wen et al., 2017(Wen et al., , 2018. The Missing Link models involving south China have been challenged by Merdith et al. (2017) who argued that a viable mechanism would first need to be proposed to explain the complexity of flowlines, significant rotation of cratonised southern China, and rapid rates of rifting that were required to achieve the Missing-Link configuration. Merdith et al. (2017) also challenged the Tarim Block Missing Link models on the basis of inconsistencies in tectonic setting along northwestern Tarim during the late-Neoproterozoic. ...
... The Missing Link models involving south China have been challenged by Merdith et al. (2017) who argued that a viable mechanism would first need to be proposed to explain the complexity of flowlines, significant rotation of cratonised southern China, and rapid rates of rifting that were required to achieve the Missing-Link configuration. Merdith et al. (2017) also challenged the Tarim Block Missing Link models on the basis of inconsistencies in tectonic setting along northwestern Tarim during the late-Neoproterozoic. ...
... T he growth of megacontinent Gondwana resulted from plate reorganization following the breakup of Rodinia during the late Neoproterozoic-Cambrian interval. Gondwana assembly involved the suturing of different blocks within the East African, Brasiliano, Damara and Kuunga orogens and concomitant destruction of the Mozambique, Brasiliano, and Damaran oceans [1][2][3][4][5][6][7][8] . The East African Orogen (EAO) is a longlived (>400 Ma) accretionary-style margin at one side of the Mesoproterozoic-Neoproterozoic Mozambique Ocean, which separated India and Azania (central Madagascar, Somalia, eastern Ethiopia and Arabia) from the rest of Africa [6][7][8][9] . ...
... Gondwana assembly involved the suturing of different blocks within the East African, Brasiliano, Damara and Kuunga orogens and concomitant destruction of the Mozambique, Brasiliano, and Damaran oceans [1][2][3][4][5][6][7][8] . The East African Orogen (EAO) is a longlived (>400 Ma) accretionary-style margin at one side of the Mesoproterozoic-Neoproterozoic Mozambique Ocean, which separated India and Azania (central Madagascar, Somalia, eastern Ethiopia and Arabia) from the rest of Africa [6][7][8][9] . Azania collided with eastern parts of Africa between 640 and 600 Ma 6 . ...
The serpentine orogenic belts that formed during the Neoproterozoic assembly of Gondwana resulted in geodynamic changes on the planet in advance of the Cambrian radiation. The details of Gondwana assembly associated with the closure of the Mozambique Ocean are enigmatic. We compile published geological and paleomagnetic data to argue that the Tarim block was associated with the Azania and Afif-Abas-Lhasa terranes and they were the locus of long-lived Andean-type subduction during the~900-650 Ma interval. Our model suggests a subduction system reorganization between 750-720 Ma, which resulted in two distinct phases of Mozambique ocean evolution. Between 870-750 Ma, a N-S oriented subduction system marks the locus of ocean crust consumption driven by the extension of the Mozambique Ocean. Beginning~720 Ma, a newly developed~E-W oriented subduction system began to consume the Mozambique Ocean and led to the assembly of eastern Gondwana. Our new reconstruction uses true polar wander to constrain the relative paleo-longitude of Tarim, South China and West Africa. In this scenario, the closure of the Mozambique Ocean and formation of Gondwana was orthogonal to the preceding super-continent Rodinia.
... We then introduce geological data in the form of plate boundaries (e.g. compilation of rifts 708 and arcs (Merdith et al., 2017b)) and use the compilation to manipulate the model in a manner that still fits 709 the palaeomagnetic data, but also accommodates geological data. Structural and metamorphic constraints 710 are used here principally to infer (where possible): (i) polarity of subduction, (ii) collision timing and (iii) 711 orientation of rifting. ...
... Corvino et al., 2008;Liu et al., 2017). In South China, this subduction is more sparse, 1636 but recent work has suggested that part of present-day Vietnam is associated with the southwestern Yangtze 1637 craton (Minh et al., 2020) proximity without collision between Australia-Antarctica and another continent (Collins, 2003;Fitzsimons, 1653Fitzsimons, 2003Halpin et al., 2017;Merdith et al., 2017b;Powell and Pisarevsky, 2002). 1654 ...
Recent progress in plate tectonic reconstructions has seen models move beyond the classical idea of continental drift by attempting to reconstruct the full evolving configuration of tectonic plates and plate boundaries. A particular problem for the Neoproterozoic and Cambrian is that many existing interpretations of geological and palaeomagnetic data have remained disconnected from younger, better-constrained periods in Earth history. An important test of deep time reconstructions is therefore to demonstrate the continuous kinematic viability of tectonic motions across multiple supercontinent cycles. We present, for the first time, a continuous full-plate model spanning 1 Ga to the present-day, that includes a revised and improved model for the Neoproterozoic–Cambrian (1000–520 Ma) that connects with models of the Phanerozoic, thereby opening up pre-Gondwana times for quantitative analysis and further regional refinements. In this contribution, we first summarise methodological approaches to full-plate modelling and review the existing full-plate models in order to select appropriate models that produce a single continuous model. Our model is presented in a palaeomagnetic reference frame, with a newly-derived apparent polar wander path for Gondwana from 540 to 320 Ma, and a global apparent polar wander path from 320 to 0 Ma. We stress, though while we have used palaeomagnetic data when available, the model is also geologically constrained, based on preserved data from past-plate boundaries. This study is intended as a first step in the direction of a detailed and self-consistent tectonic reconstruction for the last billion years of Earth history, and our model files are released to facilitate community development.
... In the context of magmatic activity at ca. 580-540 Ma in the Arabian-Nubian Shield, Northern Lhasa terrane, Tethyan Himalaya and High Himalaya associated with Gondwana assembly (Honarmand et al., 2016;Hu et al., 2016;Dong et al., 2018), an Ediacaran subduction-related setting on the southern margin of the Tarim Craton suggests a peri-Gondwanan affinity for the craton and progressive proximity to Gondwana (Fig. 11). This is consistent with other peripheral blocks with peri-Gondwanan affinity (Pereira et al., 2006;Honarmand et al., 2016;Merdith et al., 2017;Oriolo et al., 2017;Li et al., 2020;Zhang et al., 2022). Sturrock et al. (2021) suggest plume activity associated with intracratonic basin formation or continental rifting/breakup may have caused this erosion event after ca. ...
... The Precambrian Great Unconformity found across Laurentia and Gondwana (Fig. 8) may be related to the global eustasy and/or tectonic movement. The Great Unconformity in the Tarim Craton is suggestive of more intense and extensive uplift in peri-Gondwana, and its end-Ediacaran timing is consistent with Gondwana assembly (Cawood and Buchan, 2007;Meert and Lieberman, 2008;Honarmand et al., 2016;Tang et al., 2016;Merdith et al., 2017). This suggests a genetic relationship between continental uplift and the convergent setting (e.g., Pereira et al., 2006;Santosh et al., 2014;DeLucia et al., 2018;Keller et al., 2019), rather than any correlation with the late Neoproterozoic "Snowball Earth" (e.g., He et al., 2018). ...
The Great Unconformity across the Proterozoic-Phanerozoic boundary records a significant change of the Earth's continents, atmosphere, environment and life. Its origin has been assumed to be glacioeustatic mechanism in the cratonic interior. On the contrary, we provide evidences for the sub-Cambrian Great Unconformity that can be traced across the Tarim Craton (NW China) from recent geochronological and seismic data. In the interior basement uplift, a distinct unconformity over an area of 300, 000 km² presents a stratigraphic gap from the Paleoproterozoic (ca. 1.9 Ga) to the end Ediacaran. There is significant denudation beneath the Cambrian with compressional uplift. Given that the ca. 590–580 Ma Hankalchough diamictite (correlated with the Gaskiers glaciation) is absent in most areas, as much as 40 m.y. of stratigraphic gap constrained maximum span of the latest sub-Cambrian unconformity. The Precambrian uplift and denudation, and the age patterns of detrital zircon grains, overlap ca. 560–540 Ma advancing subduction process along the convergent southern margin of the Tarim Craton. This Great Unconformity may be linked to subduction-related uplift along the convergent southern Tarim margin, as occurred across peri-Gondwana. These relationships suggest tectonic driver rather than glaciation could lead to Great Unconformity in the cratonic interior as well as the continental margin
... The Neoproterozoic paleogeography of Rodinia and the mode of its breakup are still a subject of discussion (see, for example, Li et al., 2008b). While the relative positions of most of the large continental masses (i.e., Laurentia, Amazonia, Baltica, and Australia) within the Neoproterozoic supercontinent Rodinia are well constrained (e.g., Dalziel, 1992;Torsvik et al., 1996;Goodge et al., 2008;Merdith et al., 2017;Tegner et al., 2019;Robert et al., 2020;Gumsley et al., 2020), the paleogeographic positions of some of the smaller ones are not (Zuza and Yin, 2017;Zhao et al., 2018;Huang et al., 2019;Wang et al., 2021). The cratonic Tarim block is one of these entities (Wen et al., 2018;Zhao et al., 2021). ...
... The Ediacaran Period (ca. 635-541 Ma) of Earth history witnessed the final disintegration of the supercontinent Rodinia and the reassembly of Gondwana (Hoffman, 1991;Merdith et al., 2017). While the megacontinent Gondwana was assembled in the Southern Hemisphere during the Pan-African orogeny (Unrug, 1996;Meert, 2003;Collins and Pisarevsky, 2005), Laurentia was separating from Australia, Baltica, and Amazonia by protracted rifting events during the same time span (Powell et al., 1993;Bingen et al., 1998;Cawood et al., 2001). ...
In this paper, we present stratigraphic, geochemical, and geochronological data from the late Neoproterozoic sedimentary successions and volcanic sequences along the northwestern margin of the Tarim craton and characterize the rift-drift tectonics between the northern Tarim craton and the Central Tianshan terrane. We propose a regionally constrained paleogeographic reconstruction that places the Tarim craton in a central position in supercontinent Rodinia, adjacent to western North America (western Laurentia) and eastern Australia. This interpretation has strong implications for the tectonic evolution of the Tarim craton and the tectonic mode of the initial phase of Rodinia breakup during the late Precambrian–early Cambrian. We infer that the Tarim craton and the adjacent Central Tianshan terrane represent a missing link between western Laurentia and ancient Central Asia within the Neoproterozoic supercontinent Rodinia.
... The Neoproterozoic paleogeography of Rodinia and the mode of its breakup are still a subject of discussion (see, for example, Li et al., 2008b). While the relative positions of most of the large continental masses (i.e., Laurentia, Amazonia, Baltica, and Australia) within the Neoproterozoic supercontinent Rodinia are well constrained (e.g., Dalziel, 1992;Torsvik et al., 1996;Goodge et al., 2008;Merdith et al., 2017;Tegner et al., 2019;Robert et al., 2020;Gumsley et al., 2020), the paleogeographic positions of some of the smaller ones are not (Zuza and Yin, 2017;Zhao et al., 2018;Huang et al., 2019;Wang et al., 2021). The cratonic Tarim block is one of these entities (Wen et al., 2018;Zhao et al., 2021). ...
... The Ediacaran Period (ca. 635-541 Ma) of Earth history witnessed the final disintegration of the supercontinent Rodinia and the reassembly of Gondwana (Hoffman, 1991;Merdith et al., 2017). While the megacontinent Gondwana was assembled in the Southern Hemisphere during the Pan-African orogeny (Unrug, 1996;Meert, 2003;Collins and Pisarevsky, 2005), Laurentia was separating from Australia, Baltica, and Amazonia by protracted rifting events during the same time span (Powell et al., 1993;Bingen et al., 1998;Cawood et al., 2001). ...
The Tarim craton in modern Central Asia was an important component of the supercontinent Rodinia in the Neoproterozoic, although its paleogeography in Rodinia during that era is still controversial. Here, we present new stratigraphic, geochemical, and geochronological data from the Neoproterozoic sedimentary and volcanic rock successions along the northwestern margin of the Tarim craton and discuss the significance of these data and our interpretations for its tectonic evolution and paleogeographic position within Rodinia. The Lower Ediacaran sedimentary sequence (Sugetbrak Formation) in northwest Tarim includes terrestrial and shallow-marine clastic rocks intercalated with two discrete basaltic lava flows near the top. The Upper Ediacaran sedimentary sequence conformably overlying the volcanic and clastic rocks consists mainly of stromatolitic dolomite (Chigebrak Formation), representing a transgressive shallow-marine environment. Previous U-Pb zircon dating of the basaltic lava flows has constrained the timing of their eruption in the early Ediacaran (615 Ma). Detrital zircon U-Pb dating of a feldspar-quartz-sandstone unit situated between the two lava flows revealed an oldest age of 2517 ± 18 Ma and a youngest age of 612 ± 6 Ma, with a majority of zircon grains (n = 42) dated at 891−754 Ma (Tonian). A quartz-sandstone unit above the upper lava flow revealed an oldest age of 2724 ± 15 Ma and a youngest age of 607 ± 8 Ma, with a missing age group of 891−800 Ma. These data and observations indicate: (1) a major switch in the depositional setting from a terrestrial (synrifting) to shallow-marine environment following the eruption of the upper lava unit; and (2) an abrupt disappearance of the source rocks of the 891−800 Ma zircons and sediments from the provenance of the post-615 Ma (postrifting) sedimentary sequence. The basaltic rocks have low SiO2 and MgO but high total Fe2O3 and TiO2 contents (2.34−3.19 wt%), analogous to high-Ti basalts and continental flood basalts. Their Ti/V ratios (65−88), low Th/Nb ratios (∼0.1), and high TiO2/Yb ratios (∼1.1) are similar to those of ocean-island basalt (OIB). Combined with their Sm/Yb and La/Sm ratios and Sr-Nd-Pb-Hf isotope values, we infer that magmas of the Sugetbrak basalts were likely derived from partial melting of an enriched mantle source (EM I) in a transitional spinel-garnet lherzolite field. This petrogenetic evolution was a result of mantle plume−influenced rift magmatism during the Ediacaran breakup of Rodinia. The Central Tianshan terrane, which was attached to the northern Tarim craton until the Ediacaran Period, was the provenance of 891−800 Ma (Tonian) zircons in the synrift sedimentary succession. As the Central Tianshan terrane broke away from the Tarim craton after ca. 615 Ma, Tonian-aged zircons were no longer available to the depocenter of the postrift sedimentary sequence. The transition from rifting to drifting between the Tarim craton and the Central Tianshan terrane marked the final breakup of Rodinia, a global event that was possibly driven by mantle plume activities coeval with the development of the Central Iapetus magmatic province in Laurentia during the Ediacaran.
... The Neoproterozoic (1000-539 Ma) witnessed major changes in the disposition of the Earth's principal continental fragments and in the evolution of its oceans, atmosphere and biosphere (e.g., Li et al., 2008Li et al., , 2013Meert, 2008;Nance et al., 2014;Merdith et al., 2017). Protracted breakup of Rodinia at ca. 830-550 Ma overlapped with the assembly of Gondwana at ca. 660-470 Ma (Meert, 2003;Collins and Pisarevsky, 2005;Cawood and Buchan, 2007;Gray et al. 2008;Key et al., 2012;Goscombe et al., 2017). ...
... Protracted breakup of Rodinia at ca. 830-550 Ma overlapped with the assembly of Gondwana at ca. 660-470 Ma (Meert, 2003;Collins and Pisarevsky, 2005;Cawood and Buchan, 2007;Gray et al. 2008;Key et al., 2012;Goscombe et al., 2017). The configuration of the core continental fragments during the period of overlap (660-600 Ma) is relatively well constrained, but the absolute and relative positions of some cratons, particularly North China, South China and the Tarim Craton in China, remain uncertain (e.g., Li et al., 2008Li et al., , 2013Cawood et al., 2013;Tang et al., 2016;Merdith et al., 2017;Wen et al., 2017). However, long-lived, mantle superplume-related breakup of the outer blocks of Rodinia seems unlikely given the circum-Rodinia subduction system proposed to account for a history of prolonged accretionary orogenesis (e.g., Cawood et al., 2013Cawood et al., , 2016Nance et al., 2014). ...
The Tarim Craton records protracted late Neoproterozoic rifting that overlaps with the breakup of Rodinia and assembly of Gondwana. However, the timing and interactions of these two tectonic processes remain contested. To constrain the tectonic significance of this prolonged rifting event, we present LA-ICP-MS zircon U–Pb ages and geochemical data from mafic and (meta)sedimentary rocks at the top of the craton’s Ediacaran succession. Two basalt samples from the northwestern Tarim Craton contain inherited zircon grains with a wide range of U–Pb ages, the youngest at ca. 620±11 providing a maximum age for the magmatism. The youngest detrital zircon U–Pb ages from the southwestern and northern Tarim Craton are ca. 607 Ma and 617 Ma, respectively. Integrated with compiled magmatic and detrital zircon U–Pb ages, our study suggests that an episode of latest Neoproterozoic (ca. 620-600 Ma) magmatism occurred throughout the Tarim Craton. The Ediacaran mafic rocks form a transitional eruptive series between alkali and tholeiitic basalts derived from lithospheric mantle with slight crustal contamination and formed in an intra-continental rifting environment through mantle reactivation during post-subduction extension. Positioned at the outer margin of Rodinia, it is considered unlikely that the magmatism records prolonged plume-related breakup. Instead, it is thought to reflect rifting of an active continental margin in a fashion analogous to many of the peri-Gondwanan terranes, possibly related to the subduction mechanism of supercontinental breakup.
... Constraining the age of the consumed ocean basins relative to the age of a preexisting supercontinent during supercontinent assembly can provide key constraints on models of supercontinent assembly and dispersal (Hoffman, 1991;Murphy and Nance, 2003). Most proposed models for the breakup of Rodinia, leading to the assembly of Gondwana, invoke the consumption of pre-Rodinia oceans (e.g., the hypothesized Mirovoi superocean) rather than oceans newly formed during the breakup of Rodinia (Hoffman, 1991), and some involve rotation of continental blocks (e.g., counterclockwise rotation of India -Johansson, 2014;Merdith et al., 2017Merdith et al., , 2021; clockwise rotation of Tarim- Wen et al., 2018;Huang et al., 2019). ...
... ). Among these, counterclockwise rotation of India (>90°;Johansson 2014;Merdith et al., 2017) and clockwise rotation of Tarim (>45°;Wen et al., 2018;Huang et al., 2019) have been implicated.In northeast Gondwana, subduction of the Proto-Tethys oceanic lithosphere was initiated at ca. 530 Ma and closed by ca. 430-420 Ma to form the Oytag-Kudi suture, represented by the ca. ...
Constraining the positions of, and interrelationships between, Earth’s major continental blocks has played a major role in validating the concept of the supercontinent cycle. Minor continental fragments can provide additional key constraints on modes of supercontinent assembly and dispersal. The Tarim craton has been placed both at the core of Rodinia or on its periphery, and differentiating between the two scenarios has widespread implications for the breakup of Rodinia and subsequent assembly of Gondwana. In the South Tarim terrane, detrital zircon grains from Neoproterozoic–Silurian strata display two dominant populations at 950–750 and 550–450 Ma. Similarly, two main peaks at 1000–800 and 600–490 Ma characterize Neoproterozoic–Ordovician strata in northern India. Moreover, the two dominant peaks of South Tarim and north India lag two global peaks at 1200–1000 and 650–500 Ma, which reflect Rodinia and Gondwana assembly, arguing against a position within the heart of the two supercontinents. Ages and Hf isotopes of Tarim’s detrital zircons argue for a position on the margin of both supercontinents adjacent to north India with periodic dispersal through opening and closing of small ocean basins (e.g., the Proto-Tethys). Alternating tectonic transitions between advancing and retreating subduction in North Tarim coincide with periodic drift of South Tarim from north India in Rodinia and Gondwana, emphasizing the importance of retreating subduction in supercontinent dispersal. Moreover, the Rodinia-related orogenic belts spatially overlap the Gondwana-related orogenic belts in the two blocks, indicating no significant relative rotation of India and Tarim during the evolution from Rodinia to Gondwana.
... This time frame coincides with the terminal phase of the globally operative Grenvillian orogeny (ca. 1200-900 Ma) that assembled the supercontinent Rodinia (Li et al. 2008;Merdith et al. 2017), but the position of R-EG in the broad framework of Rodinia is controversial (Merdith et al. 2021 and references therein). Whether R-EG was a part of Rodinia or not, the tectonic evolution of this composite belt offers important constraints on Proterozoic continental assembly and dispersal involving India and East Antarctica. ...
A suite of mafic granulite enclaves within mylonitised felsic gneiss occurring along the E‐W trending Mahanadi Shear Zone of the Eastern Ghats Province preserves evidence of high‐pressure metamorphism. Garnet‐clinopyroxene‐bearing mafic granulite contains a mineral assemblage of garnet + clinopyroxene + plagioclase + quartz + rutile which was formed after dehydration melting of a hornblende‐bearing protolith during M 1 metamorphism that peaked at 1.1–1.4 GPa, 760°C–840°C. The retrograde stage (M 1R ) is marked by the formation of hornblende and symplectic intergrowth of clinopyroxene + plagioclase + orthopyroxene after garnet at 0.8–0.9 GPa, 760°C–810°C, suggesting an isothermal decompression type P–T path. The whole rock trace element and REE characteristics suggest a MORB‐OIB protolith for the mafic granulites. The host felsic gneiss has a granitic protolith which was emplaced in an arc setting. The rocks exposed south of the Mahanadi Shear Zone in the Phulbani domain are represented by granulites with contrasting metamorphic characteristics. The garnet‐orthopyroxene‐bearing mafic granulite within coarse‐grained charnockite and the aluminous granulite within felsic gneiss show evidence of biotite dehydration melting. The peak M 1 assemblage in the aluminous granulite is represented by the assemblage spinel + garnet + quartz + plagioclase + K‐feldspar which was stable at 0.70–0.74 GPa, 904°C–935°C. M 1R in this rock is characterised by coronas of garnet and sillimanite over spinel and the formation of matrix biotite at 707°C–806°C by near‐isobaric cooling. Similar isobaric cooling has been documented from the formation of garnet, clinopyroxene and quartz coronas on orthopyroxene in mafic granulite and garnet and quartz coronas on clinopyroxene, wollastonite and calcite in calc‐silicate granulite. The juxtaposition of lower crustal rocks showing clockwise and counterclockwise P–T paths across the Mahanadi Shear Zone implies a paired metamorphic character in a subduction–collision setting. Zircon U‐Pb and monazite U‐Th‐total Pb data show a complex history of the rock suite. The enclave suite of rocks within the Mahanadi Shear Zone underwent peak M 1 metamorphism at ca. 980–960 Ma which was followed by decompression to a shallower level by ca. 960 Ma when the host granitic magma crystallised. Rocks occurring in the Phulbani domain (southernly placed crustal domain), on the other hand, underwent ultrahigh temperature metamorphism at shallower crustal levels broadly at the same time. We argue that the southern Phulbani domain of the Eastern Ghats Province, India, collided with the Angul‐Prydz domain of the Rayner Province, East Antarctica which eventually caused underthrusting of the former below the latter across the Mahanadi Shear Zone. In the context of the Eastern Ghats‐Rayner reconstruction, this indicates the closure of the intervening Mawson Sea. A second metamorphic event (M 2 ) reworked the exhumed deep crustal rocks at ca. 900 Ma during the final docking of the Eastern Ghats‐Rayner belt against cratonic India. Our results clearly show that the Angul domain is an exotic block, and the Mahanadi Shear Zone is a terrane boundary shear zone suturing discrete domains of the Rayner‐Eastern Ghats orogen.
... Jasperoids (hematitic cherts) are one of the Fe-Si-rich rocks associated with Neoproterozoic metavolcanics in the Arabian-Nubian Shield (ANS), which is the largest ancient belt on the Earth and was formed during East and West Gondwana collision [1][2][3][4][5]. The famous island arc metavolcanic rocks in Egypt are named Shadli metavolcanics (in this study) that hosted jasperoid lenses and veins and are considered the important crustal component of the ANS [6,7]. ...
The Wadi Ranga sulfidic jasperoids in the Southern Eastern Desert (SED) of Egypt are hosted within the Neoproterozoic Shadli metavolcanics as an important juvenile crustal section of the Arabian Nubian Shield (ANS). This study deals with remote sensing and geochemical data to understand the mechanism and source of pyritization, silicification, and hematization in the host metavolcanics and to shed light on the genesis of their jasperoids. The host rocks are mainly dacitic to rhyolitic metatuffs, which are proximal to volcanic vents. They show peraluminous calc-alkaline affinity. These felsic metatuffs also exhibit a nearly flat REE pattern with slight LREE enrichment (La/Yb = 1.19–1.25) that has a nearly negative Eu anomaly (Eu/Eu* = 0.708–0.776), while their spider patterns display enrichment in Ba, K, and Pb and depletion in Nb, Ta, P, and Ti, reflecting the role of slab-derived fluid metasomatism during their formation in the island arc setting. The ratios of La/Yb (1.19–1.25) and La/Gd (1.0–1.17) of the studied felsic metatuffs are similar to those of the primitive mantle, suggesting their generation from fractionated melts that were derived from a depleted mantle source. Their Nb and Ti negative anomalies, along with the positive anomalies at Pb, K, Rb, and Ba, are attributed to the influence of fluids/melt derived from the subducted slab. The Wadi Ranga jasperoids are mainly composed of SiO2 (89.73–90.35 wt.%) and show wide ranges of Fe2O3t (2.73–6.63 wt.%) attributed to the significant amount of pyrite (up to 10 vol.%), hematite, goethite, and magnetite. They are also rich in some base metals (Cu + Pb + Zn = 58.32–240.68 ppm), leading to sulfidic jasperoids. Pyrite crystals with a minor concentration of Ag (up to 0.32 wt.%) are partially to completely converted to secondary hematite and goethite, giving the red ochre and forming hematization. Euhedral cubic pyrite is of magmatic origin and was formed in the early stages and accumulated in jasperoid by epigenetic Si-rich magmatic-derived hydrothermal fluids; pyritization is considered a magmatic–hydrothermal stage, followed by silicification and then hematization as post-magmatic stages. The euhedral apatite crystals in jasperoid are used to estimate the saturation temperature of their crystallization from the melt at about 850 °C. The chondrite (C1)-normalized REE pattern of the jasperoids shows slightly U–shaped patterns with a slightly negative Eu anomaly (Eu/Eu* = 0.43–0.98) due to slab-derived fluid metasomatism during their origin; these jasperoids are also rich in LILEs (e.g., K, Pb, and Sr) and depleted in HFSEs (e.g., Nb and Ta), reflecting their hydrothermal origin in the island arc tectonic setting. The source of silica in the studied jasperoids is likely derived from the felsic dyke and a nearby volcanic vent, where the resultant Si-rich fluids may circulate along the NW–SE, NE–SW, and E–W major faults and shear zones in the surrounding metavolcanics to leach Fe, S, and Si to form hydrothermal jasperoid lenses and veins.
... kbar; Kuribara et al., 2019) and HT to UHT metamorphism in Androyan Group of Madagascar ($560-530 Ma; 950-1000°C at 8-11 kbar; Jöns and Schenk, 2011). Similar high-grade metamorphic events have been reported throughout the Madurai, Trivandram, Salem and Nagercoil blocks in Southern India ($550-500 Ma; 940-1150°C at 7-11 kbar; Plavsa et al., 2015), Highland Complex of Sri Lanka ($580-530 Ma; 925-1150°C at 9.0-12.5 kbar; Santosh et al., 2014;Dharmapriya et al., 2015) and Prydz bay belt of Antarctica ($570-500 Ma; 800-1000°C at 9.0-13.5 kbar; Merdith et al., 2017;Spreitzer et al., 2021). Along the eastern margin of India, the evidence of the Kuunga orogeny have been locally preserved in Eastern Ghats ($550-500 Ma; Bose and Dasgupta, 2018). ...
... The Yudnamutana, Baratta and Torrowangee troughs ( Fig. 1) are major extensional sub-basins bounded by mappable normal growth faults (Preiss, 1985;Preiss & Conor, 2001;Preiss et al. 2011). This normal faulting has been interpreted to record the final phase of rifting associated with continental separation (Preiss, 2000), although Merdith et al. (2017) considered that the rift-drift transition of the Australia-Laurentia margin occurred earlier at c. 780 Ma. While the debate regarding timing of rift-drift transition is beyond the scope of this research, it is unlikely to be resolved in the northern regions of the basin given it is distal to the margin of the palaeo-Pacific Ocean. ...
The glaciogenic nature of the Yudnamutana Subgroup was first recognized over a century ago, and its global significance was recognized shortly after, with the eventual postulation of a global Sturtian Glaciation and Snowball Earth theory. Much debate on the origin and timing of these rocks, locally and globally, has ensued in the years since. A significant corpus of research on the lithology, sedimentology, geochronology and formal lithostratigraphy of these sequences globally has attempted to resolve many of these debates. In the type area for the Sturtian Glaciation, South Australia’s Adelaide Superbasin, the lithostratigraphy and sedimentology are well understood; however, formal stratigraphic nomenclature has remained complicated and contested. Absolute dates on the stratigraphy are also extremely sparse in this area. The result of these longstanding issues has been disagreement as to whether the sedimentary rocks of the Yudnamutana Subgroup are truly correlative throughout South Australia, and if they were deposited in the same time span recently defined for Sturtian glacial rocks globally, c. 717 Ma to c. 660 Ma. This study presents a large detrital zircon study, summarizes and compiles existing global geochronology for the Sturtian Glaciation and revises the formal lithostratigraphic framework of the Yudnamutana Subgroup. We show equivalence of the rocks that comprise the revised Sturt Formation, the main glaciogenic unit of the Yudnamutana Subgroup, and that it was deposited within the time span globally defined for the Sturtian Glaciation.
... In contrast, the detrital zircon populations of the Amazonian craton show a near continuous distribution throughout the Mesoproterozoic, from 1.6 to 1.0 Ga(Tassinari & Macambira 1999). Similar continuous Mesoproterozoic distributions also applies for Baltica (Johansson 2014), the Volta Basin (Kalsbeek et al. 2008), the Congo craton (Bernard et al. 2021) and the Algerian Sahara (Linnemann et al. 2011).The similar continuous range of Mesoproterozoic ages shared by the Amazonian Craton (e.g.,Tassinari et al. 2000) and Baltica (e.g.,Merdith et al. 2017) would suggest their settings adjacent to the margins of the West African craton as a patchwork of the Meso-to Neoproterozoic Rodinia supercontinent. Mesoproterozoic magmatic sources are common in the Arabian -Nubian Shield, Baltica, Amazonia, Laurentia and other Grenvillian terranes(Ernst et al. 2008), but are presumed to be absent in the West African craton and the Tuareg Shield.The "Mesoproterozoic gap" paradigm has undergone many vicissitudes due to the intermittent presence of Mesoproterozoic zircon grains in Morocco and SW Europe. ...
The Cambrian Atlas – Ossa-Morena – Northarmorican Rift extended along West Gondwana from the end of the Pan-African and Cadomian orogenies until the diachronous beginning of drift conditions related to the opening of the Rheic Ocean. The along-axis rift crosscut the western parts of the Anti-Atlas, High Atlas and Coastal Meseta, which were linked to the Ossa-Morena Zone and the North-Armorican Domain, whereas several joint tectonic branches connected with off-axis rift transects of the Central Iberian, West Asturian-Leonese and Cantabrian Zones (Iberian Massif), Central and Southern Armorican Domains, Occitan Domain, Pyrenees and southern Sardinia. The pre-rift unconformity, post-dating the orogenic collapse, is characterized by initial (half-)graben development and subsequent infill with slope-related breccias and conglomerates controlled by the denudation of surrounding uplands. Syn-rift pulses show regional extension and are distinctly identifiable on the top of rift shoulders recording episodes of carbonate production due to their association with karst and hydrothermal processes. The break-up unconformity ranges from volcanic-free angular discordances and paraconformities to generalized uplift and denudation of subaerially exposed areas, associated with the onset of granite-dominant LIPs. The Furongian–Tremadocian (Toledanian) and Ordovician (Sardic) Phases have been interpreted as due to (i) Andean-type subduction magmatism reaching the crust in an arc-to-back-arc setting, (ii) post-collisional decompression melting without significant mantle involvement, and (iii) partial melting of the lower continental crust affected by the underplating of hot mafic magmas linked to superplumes.
... The evolution of African basins must be considered in view of periodic plumes rising under the African Plate and also the climate that changed with sea-level changes accompanying the northward drift of the supercontinent during the transgressions-regressions Phanerozoic cycles, which have a direct influence on basin fill. The majority of the Phanerozoic tectonism and magmatism within the African Plate can be considered to have occurred along broad lineaments, which represent the reactivation and exploitation of earlier Late Proterozoic Pan-African sutures (Merdith et al., 2017;Unrug, 1997). Several Phanerozoic magmatic events have been identified (Issawi & Gayed, 2011;Fig. ...
Egypt is located in northeastern portion of Africa and extends into the Asian near East. It is susceptible to many local and global tectonic events with sea-level changes during deposition of the Phanerozoic sediments. The Paleozoic history of Egypt showed that the sediments were meagerly comparing with the Mesozoic and Cenozoic. The most important structures which had a great effect on the stratigraphy of Egypt stretched from the northern shores of Egypt to its extreme southern part. The controlling factor in the development and distribution of the Paleozoic is rolled by several high arcs which stretch from south to north, irregularity with Pre-Cambrian and Paleozoic plumes (541–431 ± 20–30 Ma). Important glaciation sediments were recorded during the infra-Cambrian of the Hammamat sediments and Late Ordovician–Early Silurian Gabgaba Formation at southeast Egypt and Al Gilf Kebir which stretching from the northwestern part of Africa to the Arabian Plate. The Mesozoic deposits in Egypt are very unequally distributed. Marine Triassic is only known from the Arif El Naga dome in northeast Sinai, where continental Triassic covers more areas in Egypt. Marine Jurassic deposits were recorded from the north and northeast Sinai as well as from the western side of the Gulf of Suez. The best and most complete section of the Jurassic is exposed at Gebel Maghara North Sinai. On the other hand, Jurassic fluvio-marine and fluviatile sections were mapped from the southern parts of the country as far as lat. 23° 30′ N. Subsurface marine and continental sequences were identified in the subsurface of the north Western Desert. The transition from Jurassic to Cretaceous history was marked by a major and widespread hiatus in Egypt due to Cimmerian Event. Cretaceous deposits are widely distributed on the surface and subsurface covering about 40% of the total area of Egypt extending from north Sinai to the Egyptian–Sudanese border. Remarkable facies and thickness variations are noted in Egypt. Where Egypt was covered by a thin blanket of Mesozoic sediments in paleo-high areas, thick sections were deposited in trough areas in-between the arcs. The Early Cenozoic marine transgression covered most of Egypt and even penetrated inside Sudan. The history of the Cenozoic in Egypt witnessed three major events named: (1) closure of the Neo-Tethys; (2) rifting of the Gulf of Suez associated with the gradual uplift of the Red Sea Basement Mountains; and (3) Messinian Crises leading to the desiccation of the Mediterranean.KeywordsGlobal eventsPhanerozoicPaleozoic arcsCimmerian eventMessinian crisesNeo-Tethys
... Many of these models reconstructed a singular moment in the geological past, and those that represented a temporal evolution were often presented as a series of static reconstructions at discrete, widely spaced time intervals. Consequently, the movement of crustal blocks in between time steps was only indicative, sometimes implying physically improbable transitions, or movements inconsistent with the implied plate boundary configurations 119 . Models were not readily testable or reproducible because no finite rotation sequences were reported. ...
The evolving mosaic of tectonic plates across the surface of the Earth sets boundary conditions for the evolution of biotic and abiotic processes and helps shape the dynamics of its interior. Reconstructing plate tectonics back through time allows scientists from a range of disciplines (such as palaeobiology, palaeoclimate, geodynamics and seismology) to investigate Earth evolution through these spatiotemporal dimensions. However, the variety and complexity of plate reconstructions can lead to some of their limitations being overlooked. In this Technical Review, we discuss the domain-specific knowledge underpinning modern quantitative plate reconstructions and convey a set of principles on how to use (but not abuse) the software or results. Open-source plate tectonic reconstruction software, like GPlates, has led to a major shift in working practices, handing non-specialists the tools to develop and integrate reconstructions based on their own datasets and expertise. However, there is no ‘one-size-fits-all’ and users need to understand what data and underlying assumptions go into making different, sometimes competing reconstruction models. It is therefore essential to consider the many ways reconstructions simplify reality when interpreting them to avoid circular reasoning. Although many aspects of deep-time reconstructions remain unresolved, future work on intercomparisons between models and uncertainty quantification is an essential pathway towards next-generation plate reconstructions. The advent of advanced plate tectonic reconstruction software has instigated an explosive growth in their generation and use by the wider Earth science community. This Technical Review provides a best-practice guide for quantitative plate reconstructions and their applications. Plate tectonic reconstructions have evolved from simple, rigid reconstructions to ones that incorporate the time-dependent evolution of plates and their boundaries, deformation and/or the history of subduction from seismic tomography.Reconstructions can be powerfully predictive for a wide range of disciplines beyond tectonics, including palaeobiology, palaeoclimate, geodynamics and seismology.With the advent of community-driven, open-source software and tools, plate models have become accessible and practicable to the wider geosciences community.With this accessibility comes a responsibility for specialists and non-specialists alike to understand how these plate models are built, their weaknesses and pitfalls and how they can be used effectively to ensure correct inferences are made.When reconstructing the tectonic plates of the Earth, there is no ‘one-size-fits-all’. Different data types and techniques are more applicable for different time periods, resolutions and purposes, for example, palaeomagnetics for pre-Pangea time periods.Important areas of ongoing research include the quantification of uncertainty, incorporation of machine learning techniques and linking reconstructions to physics-based deep Earth models and surface (and/or biogeochemical) models. Plate tectonic reconstructions have evolved from simple, rigid reconstructions to ones that incorporate the time-dependent evolution of plates and their boundaries, deformation and/or the history of subduction from seismic tomography. Reconstructions can be powerfully predictive for a wide range of disciplines beyond tectonics, including palaeobiology, palaeoclimate, geodynamics and seismology. With the advent of community-driven, open-source software and tools, plate models have become accessible and practicable to the wider geosciences community. With this accessibility comes a responsibility for specialists and non-specialists alike to understand how these plate models are built, their weaknesses and pitfalls and how they can be used effectively to ensure correct inferences are made. When reconstructing the tectonic plates of the Earth, there is no ‘one-size-fits-all’. Different data types and techniques are more applicable for different time periods, resolutions and purposes, for example, palaeomagnetics for pre-Pangea time periods. Important areas of ongoing research include the quantification of uncertainty, incorporation of machine learning techniques and linking reconstructions to physics-based deep Earth models and surface (and/or biogeochemical) models.
... The Neoproterozoic successions include mafic to intermediate igneous rocks, volcaniclastic rocks, and siliciclastic and carbonate rocks, which document the assembly of the South China Block . Igneous rocks range in age from 890 Ma to 700 Ma but with most in the range 830-750 Ma ) Paleomagnetic data integrated with comparative studies of stratigraphy, sedimentology and detrital age patterns of Cryogenian to Ediacaran rock units indicated that South China and North India were attached through the Neoproterozoic Merdith et al., 2021;Qi et al., 2018) and occupied a mid-latitude northern hemisphere location from ca. 720-635 Ma (Zhang et al., 2013), subsequently migrating to an equatorial position from ca. 635-541 Ma, consistent with its inferred position in Gondwana (Cawood et al., 2021;Jing et al., 2015;Macouin et al., 2004;Merdith et al., 2017;Merdith et al., 2021). ...
The Neoproterozoic snowball Earth hypothesis emerged to explain an inferred planetary wide extreme climate change. However, storm deposits requiring open water conditions in the Huangdongzigou Formation, South China, contradict interpretations of a global Cryogenian hard snowball Earth. These deposits accumulated during the middle Sturtian interval (690–675 Ma) on the basis of U-Pb zircon age data from andesitic tuff and coarse siltstones within the formation. Siltstones and mudstones with abundant storm-generated erosional and sedimentary structures, such as hummocky and swaley cross-stratification occur through the sedimentary succession, which require the action of oscillating ice-free water flow. Chemical weathering indices and resultant mean annual temperature calculations indicate a warm-humid environment during storm events, with the transition to a cold water depositional environment towards the top of the formation, which is possibly related to the next glacial episode.
... The timing and origin of spatially distributed felsic magmatic rocks of Neoproterozoic time from the Asian terranes provide evidence on the assembly, growth and break-up of the Rodinia supercontinent (e.g., Zhao et al., 2018). Various studies on the paleogeographic reconstruction of Pamir, Tarim, Qiangtang, and Lhasa Terranes from East-Asia suggest the location of these continental blocks on the northwestern margin of the Rodinia supercontinent (eg., Condie, 2001;Li et al., 2008;Dong et al., 2011;Cawood et al., 2013;Cawood et al., 2016;Merdith et al., 2017;Zhao et al., 2018;Hu et al., 2018a;Hu et al., 2018b;Zhou et al., 2019;Kang et al., 2019). Later, these East Asian terranes formed the part of Gondwanaland during the Paleozoic hence all belong to Gondwanan ancestry (Crawford, 1974;Şengör 1984;Yeh and Shellnutt, 2016). ...
The Karakoram Terrane (KT) represents the southern margin of the Eurasian Plate, mainly consisting of Late Jurassic-Early Cretaceous subduction-related granites and post-collisional Miocene leucogranites, which intrude the Late Neo-Proterozoic basement. We report for the first time the existence of the Cryogenian KT basement as recorded from the geochemistry and geochronology of tonalite gneiss (ca. 806 Ma) in the southeastern Karakoram terrane, NW India. Geochemically, the studied tonalite gneiss is slightly peraluminous (Molar Al2O3/CaO+Na2O+K2O=1.1), calc-alkaline volcanic-arc granitoid, strongly fractionated REE (LaN/YbN=33.99), and high Sr/Y =19.75, more akin to its affinity with Tonalite–trondhjemite–granodiorite (TTG)/adakite. The whole-rock elemental data suggest that tonalite gneiss is more likely sourced from ancient mafic lower crust where garnet remained in the residue. The petrogenetic modeling of REE suggests that the melt similar to the observed tonalite gneiss can be generated through ∼50% partial melting of a mafic lower crust with garnet, clinopyroxene, and amphibole assemblage. The synthesis and comparison of present and published Proterozoic magmatic records on the rocks from KT strongly dictate that the produced partial melt similar to observed tonalite gneiss most likely served as the parental melt for the development of TTGs in the Southern Pamir and more evolved granitoid in the Central Tibetan terrane. We propose that the studied tonalite gneiss from the southeast Karakoram is a product of Neoproterozoic Andean-type orogeny formed on the northwestern margin of the Rodinia supercontinent. Thus, our study favors the first time, the position of KT within the Cimmerian belt along with other East Asian continental blocks.
... These mobile belts comprise domains with lithostratigraphic units and structures that reveal different tectonic events and magmatic intervals related to Western Gondwana assembly (Alves et al., 2016;Balis et al., 2020;Basei et al., 2018;Basei et al., 2008a;Degler et al., 2017;Duffles et al., 2016;Faleiros et al., 2011;Heilbron et al., 2008;Schmitt et al., 2004;2008). The two main periods of tectonic activity, an older Tonian (1000-720 Ma) to Cryogenian (720-635 Ma) followed by a younger Ediacaran to Cambrian , contributed with the amalgamation of this supercontinent (Brito Neves et al., 2014;Cawood and Bunchan 2007;Merdith et al., 2017a;Schmitt et al., 2018). These events are recorded by magmatism in continental/oceanic arcs and/or crustal melting in a collisional setting, and as metamorphic phases within these tectonic domains (Basei et al., 2010;Fernandes et al., 2015;Silva et al., 2005). ...
In the southeastern Brazilian margin, a Neoproterozoic to the Early Paleozoic long-term magmatic interval is recorded within the Oriental Terrane, part of the Ribeira Orogen, characterizing it as a hot orogenic belt. Metaigneous and igneous rock units of ca. 570–540 Ma and 510–480 Ma are coeval with two main collisional orogenies related to the Western Gondwana assembly: the Ribeira Orogeny (590–565 Ma) and the Búzios Orogeny (540–490 Ma). The Oriental Terrane, interpreted as a continental microplate amalgamated during the convergence between the São Francisco and Congo cratons, comprises Cryogenian to Ediacaran metaigneous rocks and Cambro-Ordovician plutons intrusive in metasedimentary sequences. Zircons from an orthogneiss and a porphyritic leucogneiss sample gave SHRIMP U-Pb crystallization ages of 558 ± 2 Ma and 560 ± 2 Ma, respectively, with high δ¹⁸O values from 7 ‰ to 10 ‰. Zircons from a tonalite pluton and tonalitic dikes, gave SHRIMP U-Pb crystallization ages of 483 ± 2 Ma and 492 ± 2 Ma, with lower δ¹⁸O values, between 6 ‰ to 8 ‰. These two magmatic pulses, integrated with a compiled database from other plutons in this terrane, corroborate with the hypothesis that they represent crustal scale magmatic provinces here interpreted as pre- and post-collisional in relation with the Búzios Orogeny. Their distribution within the tectonic map of the Oriental terrane reflect a paleogeography linked to their tectonic origin. The 570–540 Ma plutons are aligned ENE -WSW, parallel and close to the suture zone with the Cabo Frio Tectonic Domain, representing a crustal melt related to a NW-subduction. A subsequent magmatic hiatus of 30 ma is interpreted as the collision of the Cabo Frio Tectonic Domain. The post collisional period is marked the intrusion of non– linear 510–480 Ma pluton, widespread in the Oriental terrane.
... As the prospect of continuous global paleogeographic modeling into Precambrian time draws ever nearer Pisarevsky et al., 2014a;Pehrsson et al., 2016;Merdith et al., 2017Merdith et al., , 2021, researchers must decide which paleomagnetic poles are the most essential to honor in kinematic reconstructions. Various classification systems have been devised in past decades, including sequential grades (Briden and Duff, 1981) and point scales (e.g., Stewart and Irving, 1974;Van der Voo, 1990;Buchan, 2013;Meert et al., 2020). ...
We present a compilation of reliable Precambrian paleomagnetic poles from three successive international workshops (in years 2009, 2014, 2017), comprising paleomagnetists specializing in Precambrian tectonic reconstructions. The working groups compiled lists of two global classes of poles, published through the end of 2017.
“Grade-A” results are judged to provide essential constraints on tectonic reconstructions; “Grade-B” poles are judged to be suggestive of high-quality, but not yet demonstrated to be primary, or perhaps lacking precise geochronologic or other constraints. Our catalog documents a resurgence of high-quality data acquisition in recent
years, and highlights specific cratons and time intervals that are most lacking in the data needed to reconstruct those blocks through supercontinental cycles.
... Elsewhere in the world, central Rodinia was breaking apart and ca. 715 Ma is plausibly the time of ocean crust production in the Pacific Ocean as Laurentia broke away from Australia/Mawson (Merdith et al. 2017b). This is recorded as a time of extensive rifting in the Adelaide Superbasin (Lloyd et al. 2020). ...
The limited shortening and crustal thickening in the Arabian–Nubian Shield (ANS) during central Gondwana amalgamation have preserved the pre-continental collision accretionary orogen in a manner that allows us to reconstruct past plate tectonic kinematics. We interpret this to show remarkable changes in plate tectonic motions at ca. 720 Ma that reflect a major change in subduction of the Mozambique Ocean. This is represented in the ANS by the transition from earlier (presently oriented) NE–SW trending suture zones (Bi’r Umq–Nakasib and Yanbu–Sol Hamed) to younger approximately NNW–SSE trending sutures (Keraf and Nabitah). This plate reorganization event is seen elsewhere in the planet at this time and is interpreted to represent the beginning of Neoproterozoic India’s southward progression from Tonian high latitudes to more equatorial locations as it advanced orthogonally towards the Neoproterozoic African continents on one side and obliquely against Western Australia on the other. The geology of the ANS provides vital constraints in the endeavour of reconstructing the plate tectonic circuit of the globe in deep time.
... According to the current timescale (Fig. 1a), the preceding Tonian Period now lasts 280 million years. Having originally been envisaged to encapsulate a period of lithospheric thinning (supercontinent break-up), the Tonian covers the final amalgamation of Rodinia (Evans et al. 2016;Merdith et al. 2017a) and a prolonged interval of relative stability prior to the onset of major break-up after 0.83 Ga, and perhaps as late as 0.75 Ga (Jing et al. 2020;Merdith et al. 2017b). A proliferation of sedimentary basins in Rodinia between c. 850 and 800 Ma (e.g. the Centralian Superbasin of Australia, the East Svalbard-East Greenland basin, the Mackenzie Mountains-Amundsen and associated basins of northern-northwestern Canada, the Nanhua rift basin of South China and the Central Africa Copperbelt (Rainbird et al. 1996;Lindsay 2002;Bull et al. 2011;Wang et al. 2011;Hoffman et al. 2012;Li et al. 2013), were originally interpreted to record an initial phase of Rodinia break-up (Li et al. 1999;Macdonald et al. 2012), perhaps related to insulation of the underlying mantle (Lindsay 2002) and/or the influence of a series of similarly aged mantle Fig. 5. Evolution of stratigraphic terminology for the Neoproterozoic Era. ...
The geological time scale before 720 Ma uses rounded absolute ages rather than specific events recorded in rocks to subdivide time. This has led increasingly to mismatches between subdivisions and the features for which they were named. Here we review the formal processes that led to the current time scale, outline rock-based concepts that could be used to subdivide pre-Cryogenian time and propose revisions. An appraisal of the Precambrian rock record confirms that purely chronostratigraphic subdivision would require only modest deviation from current chronometric boundaries, removal of which could be expedited by establishing event-based concepts and provisional, approximate ages for eon-, era- and period-level subdivisions. Our review leads to the following conclusions: 1) the current informal four-fold Archean subdivision should be simplified to a tripartite scheme, pending more detailed analysis, and 2) an improved rock-based Proterozoic Eon might comprise a Paleoproterozoic Era with three periods ( early Paleoproterozoic or Skourian, Rhyacian, Orosirian), Mesoproterozoic Era with four periods (Statherian, Calymmian, Ectasian, Stenian) and a Neoproterozoic Era with four periods (pre-Tonian or Kleisian , Tonian, Cryogenian and Ediacaran). These proposals stem from a wide community and could be used to guide future development of the pre-Cryogenian timescale by international bodies.
... This led to the southward journey of Neoproterozoic India to collide against African Gondwana and the Australia-Mawson continent 11 to form the kernel of Gondwana. This plate reorganization is coeval with the opening of the Pacific Basin 12,13 and directly precedes the cataclysmic climatic perturbations of the Cryogenian. ...
Plate reorganization events involve fundamental changes in lithospheric plate-motions and can influence the lithosphere-mantle system as well as both ocean and atmospheric circulation through bathymetric and topographic changes. Here, we compile published data to interpret the geological record of the Neoproterozoic Arabian-Nubian Shield and integrate this with a full-plate tectonic reconstruction. Our model reveals a plate reorganization event in the late Tonian period about 720 million years ago that changed plate-movement directions in the Mozambique Ocean. After the reorganization, Neoproterozoic India moved towards both the African cratons and Australia-Mawson and instigated the future amalgamation of central Gondwana about 200 million years later. This plate kinematic change is coeval with the breakup of the core of Rodinia between Australia-Mawson and Laurentia and Kalahari and Congo. We suggest the plate reorganization event caused the long-term shift of continents to the southern hemisphere and created a pan-northern hemisphere ocean in the Ediacaran. A Proterozoic full-plate reconstruction reveals a late Tonian plate reorganization event that resulted in consumption of the Mozambique Ocean and the concentration of continents in the Southern Hemisphere.
... The period between the breakup of Rodinia and the amalgamation of Gondwana during the Neoproterozoic (ca. 800 to 500 Ma) is interpreted to involve the reconfiguration of many of Earth's major cratonic blocks (Johansson, 2014;Li et al., 2008;Merdith et al., 2017aMerdith et al., , 2017b. Paleogeographic reconstructions at the time of Rodinia breakup vary significantly in the placement of continental blocks that now belong to the African and South American continents. ...
Neoproterozoic metasedimentary rocks in the foreland domains of the Kaoko-Dom Feliciano-Gariep orogenic system record sedimentation from the breakup of Rodinia to the amalgamation of Gondwana, and thus provide ideal subjects for investigation of the mutual pre-orogenic positions of rifted margins of the African and South American cratonic blocks. U-Pb isotopic dating of zircon in the Brusque Complex of the northern Dom Feliciano Belt, Brazil, provides new constraints on the timing and sources of Neoproterozoic sedimentation along the eastern margin of the Luis Alves Craton. The minimum age of sedimentation is constrained by a U-Pb zircon age of 811 ± 6 Ma from a dyke cross-cutting the Brusque Complex. U-Pb detrital zircon analysis reveals two distinct groups: one with ages ca. 2.2-2.0 Ga consistent with erosion of the adjacent Luis Alves Craton, and another with ages ca. 2.1-1.8 and 1.6-1.0 Ga consistent with erosion of Paleoproterozoic to Mesoproterozoic igneous provinces and/or supracrustal sequences at the edge of the Congo Craton. The age distributions match with analogous rocks of the central Dom Feliciano Belt and the Kaoko Belt, and show similarities with the Gariep Belt, suggesting deposition in a system of coeval and spatially related paleobasins around the time of Rodinia breakup. The absence of Neoproterozoic detrital zircon close to the age of sedimentation suggests deposition in an intra-continental rift or passive margin. A third group contains a significant proportion of Neoproterozoic ca. 670-560 Ma zircon, suggesting similarities with the adjacent Itajaí Basin syn-orogenic foreland sedimentary rocks. This indicates that foreland basin sediments were partly tectonically interleaved with the pre-orogenic metasediments of the Brusque Complex during late-stage orogenic deformation. The findings support an intracontinental rifting model for the formation of the Kaoko-Dom Feliciano-Gariep basin system. The data further indicate that the Luis Alves Craton was in close proximity to the Congo Craton, and likely with the Nico Pérez Terrane and the Kalahari Craton, at the onset of Tonian rifting and the breakup of Rodinia.
Ancient orogens eroded to midcrustal levels provide insight about strain accommodation, metamorphism, and melting in Himalaya-type continent-continent collisions. This study focuses on the Neoproterozoic–Cambrian Eastern-Africa / Kuunga orogen exposed in Madagascar, where uncertainty about the terrane correlations, and therefore structural framework, of the orogen persists. We present a comprehensive dataset of monazite petrochronology and thermobarometry across the southern Madagascar basement to quantify the regional and temporal variability of metamorphism. We argue that the ultrahigh-temperature Anosyen domain and associated Androyen domain have a shared geological history, recording two successive tectonic events at 630–600 Ma and 580–500 Ma. Other Madagascar domains record primarily the former (Vohibory domain to the west) or latter (all other domains to the northeast) event.
From this inference, we discuss terrane correlations with Africa and India, then present a structural framework for the orogen in which the Anosyen–Androyen domain was structurally confined in a central, lithosphere-scale transpressional shear system between divergent, diachronous thrust belts. By limiting exhumation, extrusion, and collapse, the structural trapping of the Androyen–Anosyen domain facilitated longer-lasting, higher- T metamorphism than associated rocks in the adjacent nappe systems. Such structural trapping may be an important control on high- T metamorphism in the cores of Himalaya-type orogens in general.
Sedimentary provenance studies using detrital zircon U–Pb ages represent an important tool to investigate the
evolution of orogenic basins and to suggest tectonic settings and paleogeography reconstructions when it comes
to supercontinent modeling. Syn-orogenic basins worldwide are characterized by a large proportion of zircons
with ages close to the maximum depositional period, reflecting the proximity of recently formed magmatic rocks.
In this work, we combine field observations, detrital zircon U–Pb ages, whole-rock Sm–Nd and mica Ar–Ar
isotopic analyses to constrain the final tectonic evolution of a restricted basin located in a poorly studied region
at the easternmost limit of the Paraguay Belt in the Tocantins Province, central Brazil. The investigated area
corresponds to the boundary sector of the Paraguay Belt and the Brasília Belt and is also transected by the strikeslip
fault system associated with the Transbrasiliano Lineament. This sector was previously mapped as part of the
Cuiaba Group, internal zone of the Paraguay Belt. We provide 465 new detrital zircon U–Pb data with ages
distributed from the early Cambrian to the Archean, with approximately 60% of the analyzed grains derived from
Ediacaran-Cryogenian sources. The maximum depositional age of the basin is defined at ca. 590 Ma, constrained
by the youngest age peak and an evident provenance shift in detrital input in the Paraguay Belt was demonstrated.
The syn-orogenic character of the basin is inferred based on the main peak of the detrital zircon population
age distribution around 600 Ma, which is very close to the maximum depositional period and points to a
short time between erosion, deposition, and burial processes. The muscovite 40Ar/39Ar age of ca. 536–546 Ma
obtained for muscovite schist metamorphosed under greenschist facies conditions indicates that the regional
thermal regime was maintained up to the early-Cambrian in the area. The minimum fast cooling rate of 25 ◦C/
Myr defined in the investigated area is constrained by the 40Ar/39Ar analysis of biotite (549.16 ± 1.30 Ma) from
a syn-to late-kinematic granodiorite intrusion. The very rapid magma emplacement occurred into relatively
shallow crustal levels through the associated strike-slip faults. The Transbrasiliano Lineament would have
facilitated the rapid unroofing of the study area and therefore the syn-orogenic deposition in a foreland domain
at the final phase of West Gondwana amalgamation. The studied metasedimentary rocks represent a transition
phase from the passive margin sedimentation (Cuiab´a Group) to an orogenic phase, constraining an inversion
event in the West Gondwana around ca. 590 Ma. The data provide evidence of a late orogenic basin that was
formed contemporaneously with the evolution of an active margin between the Amazonian Craton and the
eastern blocks/cratons (S˜ao Francisco-Congo and Rio de la Plata cratons and Paranapanema Block) close to
Cambrian times. Our results support the existence of the younger Clymene Ocean and the subsequent final assembly
of West Gondwana in the Cambrian.
Understanding the intricate relationships between the solid Earth and its surface systems in deep time necessitates comprehensive full-plate tectonic reconstructions that include evolving plate boundaries and oceanic plates. In particular, a tectonic reconstruction that spans multiple supercontinent cycles is important to understand the long-term evolution of Earth's interior, surface environments and mineral resources. Here we present a new full-plate tectonic reconstruction from 1.8 Ga to present that combines and refines three published models: one full-plate tectonicmodel spanning 1 Ga to present, and two continental-drift models focused on the late Paleoproterozoic to Mesoproterozoic eras. Our model is constrained by geological and geophysical data, and presented as a relative plate motion model in a palaeomagnetic reference frame. The model encompasses three supercontinents, Nuna (Columbia),Rodinia, and Gondwana/Pangea, and more than two complete supercontinent cycles, covering ~40% of the Earth’s history. Our refinements to the base models are focussed on times before 1.0 Ga, with minor changes for the Neoproterozoic. For times between 1.8 Ga and 1.0 Ga, the root mean square speeds for all plates range between 4 and 10 cm/yr, and the net lithospheric rotation is below 0.9°/Myr, which are kinematically consistent with post-Pangean plate tectonic constraints. The time spans of the existence of Nuna and Rodinia are updated to between 1.6 Ga (1.65 Ga in the base model) and 1.46 Ga, and between 930 Ma and 780 Ma (800 Ma in the base model), respectively, based on geological and paleomagnetic data. We follow the base models to leave Amazonia/West Africa separate from Nuna (as well as Western Australia, which only collides with the remnants of Nuna after initial break-up), and South China/India separate from Rodinia. Contrary to the concept of a "boring billion", our model reveals a dynamic geological history between 1.8 Ga and 0.8 Ga, which is characterized by supercontinent assembly and breakup, continuous accretion events, and widespread LIP events. The model is publicly accessible, providing a framework for future refinements and facilitating deep time studies of Earth's system.
Laurentia, core of the North American continent, is surrounded by Neoproterozoic to Cambrian rifted margins. This led to early suggestions that it was located within a Neoproterozoic supercontinent, Rodinia. Recent models of Precambrian palaeogeographic development also point to a ‘Laurentia-centric’ Rodinian supercontinent. Before plate tectonics, the geometry of continental margins, comparison of cratonic interiors and sedimentary covers, and orogenic piercing points were employed to postulate the geography of Phanerozoic Pangaea. Marine studies have subsequently demonstrated the results were remarkably accurate. Absent in situ Precambrian oceanic crust, the same lines of evidence are employed here to reconstruct Rodinia, together with others unavailable at that time. A strong case can be made for former juxtaposition of the Pacific margins of Laurentia and East Antarctica-Australia approximately as proposed in the 1990s, even though the precise match remains elusive. The Atlantic margin is likely to have rifted from Baltica, Amazonia and other South American cratons along the Grenvillian orogenic suture in the early Palaeozoic, although the suture itself makes accurate reconstruction difficult. A piercing point and ‘tectonic tracer’ can be used to position the Kalahari craton and Coats Land crustal block of Antarctica off the present southern margin of Laurentia and contemporaneous large igneous provinces point to Siberia being located off the Arctic margin. Hence Laurentia does appear to be the ‘Key’ to Rodinian palaeogeography even though the exact geometric fit to its surrounding cratons remains to be refined.
Deforming belts in the Arabian‐Nubian Shield (ANS) are classified into (1) suture‐related belts, including arc–arc and arc‐continental, and (2) post‐accretionary systems, including N‐trending compression zones and NW‐trending strike‐slip faults. Terrane accretion took place in the ANS between 800 and 700 Ma, along arc–arc sutures. Such sutures are directed from E to NE in the northern part of the ANS, and from N to NE in the south, and are aligned in the north and east with N‐ or S‐verging ophiolitic nappes, or in the south with W‐verging nappes. The Asir, Hijaz, and Midyan terranes formed the Western Arabian shield by 715 Ma. The Afif terrane collided with the Hijaz and Asir terranes between 680 and 640 Ma, terminating the subduction along the Nabitah suture. Subduction began west of the Al Amar arc near the margin of the Ar Rayn terrane at 670 Ma. Afif and Ar Rayn terranes collided along the Al Amar‐Idsas suture about 640 Ma, producing the Idsas orogeny that initiated the major faulting and folding. Strike‐slip faults and upright folds related to oblique convergence between terranes and/or post‐accretionary systems deform the southern sutures. The eastern and western boundaries of the ANS are marked by arc‐continental sutures and characterized by N‐trending deformation belts that formed at 750–650 Ma when the ANS collided with East and West Gondwana.
The Choquequirao Formation is a >3 km-thick amphibolite-grade succession that outcrops in the Central Andes of southern Peru. To constrain its age and tectonostratigraphic setting, detrital zircon and metamorphic zircon, titanite, and rutile U–Pb isotopic analyses were conducted. Mantle-derived c. 640 Ma detrital zircons constrain the maximum age of the lower part of the succession and 550–490 Ma metamorphic zircon domains constrain its minimum age. The absence of early Paleozoic detrital zircons suggests that deposition predated early Paleozoic orogenesis in southwestern Gondwana. The close similarity of detrital zircon age spectra to those from sediments deposited on the Arequipa basement suggests that the Choquequirao Formation was deposited on the Arequipa Terrane. Metamorphic titanite dates are highly overdispersed, yet they overlap with c. 460 Ma peak metamorphism recorded by metamorphic zircon. Pb-loss pathways displayed by metamorphic titanite have a lower intercept that overlaps with c. 325 Ma metamorphic rutile, which corresponds to Hercynian orogenesis. A poorly constrained upper intercept of c. 510 Ma may correspond to Pampean and/or early Famatinian orogenesis. We interpret the Cryogenian–Ediacaran Choquequirao Formation as having been deposited during the opening of the Palaeo-Iapetus (Puncoviscana–Clymene) Ocean between eastern Arequipa and southern Kalahari prior to the subsequent collision with southwestern Amazonia during the Pampean Orogeny.
The Choquequirao Formation is a >3 km-thick amphibolite-grade succession that outcrops in the Central Andes of southern Peru. To constrain its age and tectonostratigraphic setting, we conducted detrital zircon and metamorphic zircon, titanite, and rutile analyses. Mantle-derived ∼640 Ma detrital zircons constrain the maximum age of the lower part of the succession and 550-490 Ma metamorphic zircon domains constrain its minimum age. The absence of early Paleozoic detrital zircons suggests that deposition predated early Paleozoic orogenesis in southwestern Gondwana. The close similarity of detrital zircon age spectra to those from sediments deposited on Arequipa basement suggests that the Choquequirao Formation was deposited on the Arequipa Terrane. Metamorphic titanite dates are highly overdispersed, yet they overlap with ∼460 Ma peak metamorphism recorded by metamorphic zircon. Pb loss pathways displayed by metamorphic titanite have a lower intercept that overlaps with ∼325 Ma metamorphic rutile, corresponding to Hercynian orogenesis. A poorly-constrained upper intercept of ca. 510 Ma may correspond to Pampean and/or early Famatinian orogenesis. We interpret the Cryogenian to Ediacaran Choquequirao Formation as deposited during the opening of the PaleoIapetus (Puncoviscana - Clymene) Ocean between eastern Arequipa and southern Kalahari prior to subsequent collision with southwestern Amazonia during the Pampean Orogeny.
Supplementary material at https://doi.org/10.6084/m9.figshare.c.6266972
Brittle structures are crucial for enabling several key natural processes in the Earth's Upper Crust. In addition, understanding the 3D characteristics and geological evolution of these features is equally important to support various developmental objectives, such as those, inter alia , linked to natural gas, groundwater, hydrothermal minerals and seismicity. In this study, we map various fractures of Gondwana based on the available geological information, satellite imagery and digital elevation data. The lengths and orientations of more than 10,000 fractures in their present-day position reveal four clearly defined patterns, with those striking NW being predominant. Archean-Paleoproterozoic domains are defined by fractures oriented N and NE, whereas the Mesoproterozoic has dominant NNW striking fractures. In contrast, the Neoproterozoic has mostly NE striking fractures and the Phanerozoic sequences are defined by a predominant NW and a subordinate W fracture patterns. The style and geometry of these structures can be linked to major geodynamic events that led to the formation of Gondwana building blocks during the Eburnean (ca. 2.2-1.8 Ga), Kibaran (ca. 1.4-1.0 Ga) and Pan African-Brasiliano (ca. 800-550 Ma) orogens, and amalgamation of Pangea (ca. 350-250 Ma). Many structures have been reactivated and new faults formed during opening of the Atlantic and Indian Oceans (ca. 180-120 ma), the India-Asia collision and rifting across East Africa since about 40 Ma. Although the changes in paleogeography remain difficult to model with accuracy, major structural orientations are corroborated by the occurrence of major mineral deposits and seismicity. The spatial distribution of mapped patterns across the different continent also correlate well with large shale gas prospects and increased groundwater yields. Thus, Gondwana fractures need to be considered in more detail for informing future development related to water and energy use, especially across regions of Africa.
The striking coincidence of the Franklin large igneous province (LIP) and the Sturtian glaciation onset ca. 717 million years ago (Ma) has inspired the hypothesis that either basaltic weathering or stratospheric sulfate aerosol injection of the Franklin LIP plunged Earth into global glaciation. The cool background climate just before the Sturtian has been commonly invoked by such initiation models. Difficulty in definitively linking these concepts with geological evidence has precluded complete demonstration of a snowball trigger mechanism. Here, we report that Franklin-aged magmatism was not only present in Laurentia and Siberia, but also in South China, where the Hubei–Shaanxi Magmatic Province formed at 720 Ma, revealing widespread magmatic provinces immediately preceding the onset of the Sturtian snowball Earth. Geochronological and geochemical data suggest that the geographically widespread magmatic provinces were emplaced over a short duration (ca. 720–717 Ma) and likely related to a mantle superplume beneath supercontinent Rodinia. We propose that low-to-mid-latitude volcanism prior to the Sturtian by a few million years enhanced global weatherability and created the background cool climate for the superimposed shock of stratospheric sulfate aerosol injection of the terminal Franklin eruption. Such widespread 720–717 Ma volcanism on different continents may have driven the Sturtian snowball initiation.
Collision, high-angle contraction, crustal thickening and heating at 555–516 Ma, primed the Damara Belt ready for crustal collapse, which was triggered by a transition to ENE–WSW contraction along the length of the belt in response to orogenic events in east Gondwana at 516–505 Ma. Along-orogen shortening reworked and thickened the high-grade core of the belt, increasing gravitational instability, and establishing an NW–SE extension direction across the belt that was conducive to reactivation of pre-existing structures and eventual collapse. This extension direction persisted, and the switch to vertical σ1 and collapse was signalled by decompression melting at ∼502 Ma and subsequent rapid cooling. Collapse was focused on the high-grade core of the belt that was exhumed as a ∼170 km wide, semi-coherent massif-type metamorphic core complex with steep extensional shear zones and faults in the marginal flanks. During exhumation the core complex was reactivated by oblique-slip extensional shear zones that responded to external transient stress fields. Reactivation by middle- to lower-amphibolite facies dextral-normal shear zones at ∼500–495 Ma and ∼495–490 Ma, involved E–W to ENE–WSW shortening consistent with accretionary events in the west Gondwana margin during the Pampean Orogeny. Reactivation by greenschist facies sinistral-normal shear zones at ∼485 Ma, involved N–S shortening consistent with accretionary events in the south Gondwana margin during the Famatinian Orogen. Early stages of exhumation involved decompression melting, flattening folds and ductile ultramylonite zones within carbonate that formed by NW–SE extension. Late stage exhumation in the brittle field from ∼480 Ma onwards, involved a stress-switch to radial extension directions dominated by NE–SW. This stage involved flat-lying breccia, inclined faults, vertical fractures, and oxidizing fluids partitioned into the top of the lower-levels of the massif. Ongoing exhumation of the core complex drove localized NW–SE shortening within the flanking margins and hanging-wall, and produced low-strain reverse structures that straddle the ductile to brittle transition. The pressure difference between exhumed massif (4.8–5.5 kbar) and hanging-wall margins (3.9–4.2 kbar), indicate that ∼3.2–4.6 km of crust was stripped from above the core complex.
After a description of the main geological units and the present-day geotectonic setting before Gondwana amalgamation, this chapter summarises the tectonic evolution of the Antarctic continent from its inclusion as part of the Gondwana supercontinent to the breakup of this landmass and the repositioning of Antarctica at southern polar latitudes since the Early Cretaceous. The geological evolution of the Antarctic continent is then described considering two main time periods: (1) c. 600–450 Ma, covering the processes which were active immediately before and during the amalgamation of Gondwana; and (2) c. 450–180 Ma, including all the major events that occurred after the final stage of Gondwana amalgamation to the time immediately before the Gondwana breakup phase. A subsequent section is devoted to the 180 Ma to recent time window during which present-day Antarctica and the other southern continents and surrounding oceanic basins formed as consequence of the fragmentation of Gondwana, and when tectonic processes led to the drift and dispersion of the various continental fragments. After a general overview of the most significant plate tectonic stages, and coeval magmatic products, the chapter reviews the main geological findings from the Ross Embayement region – one of the most investigated regions in Antarctica – the Transantarctic Mountains and the Ross Sea sector of the Western Antarctic Rift System. Persistent open problems, and potential research themes, are discussed in the Conclusions.
There is ample evidence that supercontinent cycles on Earth have been operating since the Late Paleoproterozoic. Evidence for the supercontinent cyclicity arises from multidisciplinary observations from geology, geochronology, geophysics (e.g., paleomagnetism, seismology, heat flow), isotope geology, and geochemistry. This overview summarizes current views of Precambrian supercontinent episodicity or cyclicity. In addition, paleogeographic reconstructions based on global key paleomagnetic poles and kinematic models of Paleo-Mesoproterozoic Nuna supercycle, Meso-Neoproterozoic Rodinia supercycle, and the Phanerozoic Gondwana/Pangea supercycle are explored. The lifecycle of supercontinents is tested by geological, geophysical, and geochemical data coupled with secular evolution trends of Earth. Results suggest that (1) supercontinent cyclicity has a characteristic (quasi-) period of ~700-500 million years, supported by planetary secular evolutionary trends, but other periods are also present; (2) supercontinents Nuna, Rodinia, and Gondwana/Pangea have different configurations and secular evolutionary trends possibly due to different tectonic styles of assembly; (3) globally averaged plate velocity during the Precambrian reveals a wave-like pattern with peaks and lows
corresponding with features in several secular evolution indices including the distribution of U-Pb ages, passive margins, metamorphic events, tectonic proxies, and magmatic activity; (4) the data suggest three tectonomagmatic
lulls during the Proterozoic, but the proposed Mesoproterozoic quiescent period, coined as “boring billion” years of Earth history (1.8-0.8 Ga) appears to be seen mainly by atmospheric and biospheric data rather than tectonomagmatic activity; and (5) tectonic processes driving supercontinent cyclicity are interactive, with
feedbacks from all six spheres of the Earth—the geosphere, cryosphere, hydrosphere, biosphere, atmosphere, and magnetosphere.
The Gabal El Sela and Gabal Qash Amir younger granites in the Arabian Nubian Shield (ANS) occurred within the Onib- Sol Hamed suture zone in the southern Eastern Desert of Egypt. In the study area, a pluton composed of biotite granites, muscovite granites and two mica granites is crosscut by altered dibase, microgranitic and bostonite dykes with a distinctive distribution of mineralization with high concentrations of rare metals. Silicification, hematitization, kaolinitization, episyenitization and sericitization are the main hydrothermal alteration processes in these younger granites. Gabal El Sela fractured younger granite shows highly alteration, uranium enrichment and a strong enrichment in some rare elements (such as; Zr = 2287 ppm, Y = 1123 ppm and Nb = 269 ppm) whereas, the bostonite dyke (such as; Zr = 1604 ppm, Y = 709 ppm and Nb = 292 ppm). Gabal Qash Amir muscovite granite shows a favorable enrichment in some rare elements (such as; Zr = 1898 ppm, Y = 181 ppm and Nb = 966 ppm) while, the bostonite dyke (such as; Zr = 1500 ppm, Y = 711 ppm and Nb = 286 ppm).
Mineral characterization of the highly radioactive zones shows enrichment in autunite, uranophane, uranothorite, zircon, xenotime, monazite, fergusonite, samarskite and columbite. Field radiometric measurements of the studied El Sela fractured granite revealed that eU reaches up to 459.5 ppm, bostonite dyke eU reaches up to 58 ppm and altered basic dyke eU reaches up to 1625 ppm, while Qash Amir muscovite granite eU reaches up to 51 ppm and the bostonite dyke eU reaches up to 34 ppm.
Geological, mineralogical, radiometrical and geochemical studies indicated that Gabal El Sela fractured younger granite is the most promising area characterized by strong enrichment in both uranium and some rare metals mineralization than Gabal Qash Amir muscovite granite.
After tilt correction for Ediacaran thick-skinned folding, a pair of Cryogenian half grabens at the autochthonous southwest cape of Congo Craton (CC) in northwest Namibia restore to different orientations. Toekoms sub-basin trended east-northeast, parallel to Northern Zone (NZ) of Damara belt, and was bounded by a normal-sense growth fault (2 290 m throw) dipping 57° toward CC. Soutput sub-basin trended northwest, oblique to NZ and to north-northwest-trending Kaoko Belt. It was bounded by a growth fault (750 m down-dip throw) dipping steeply (~75°) toward CC. Soutput growth fault could be an oblique (splay) fault connecting a Cryogenian rift zone in NZ with a sinistral transform zone in Kaoko Belt. A transform origin for the Kaoko margin accords with its magma-poor abrupt shelf-to-basin change implying mechanical strength, unlike the magma-rich southern margin where a gradual shelf-to-basin change implies a mechanically weak extended margin. A rift−transform junction is kinematically compatible with observed north-northwest−south-southeast Cryogenian crustal stretching within CC. Post-rift subsidence of the CC carbonate platform varies strongly across the south-facing but not the west-facing shelf. A sheared western CC margin differs from existing Kaoko Belt models that posit orthogonal opening with hyper-extended continental crust. Carbonate-dominated sedimentation over southwest CC implies palaeolatitudes ≤35° between 770 and 600 Ma.
The Rayner Complex of East Antarctica and the Eastern Ghats Province (EGP) of India are thought to have been contiguous in past supercontinents like Rodinia and Gondwana. These terranes have been correlated on the basis of similar granulite facies metamorphic imprints and isotopic age data that testify to Grenvillian (1100-900 Ma) and Pan-African (650-450 Ma) thermal signatures. The Grenvillian granulite facies metamorphic event is generally thought to represent collision between Antarctica and cratonic India, but the precise location of the Indo-Antarctic suture is disputed. The intensity of Pan-African age geological imprints is also variable in both continents, and their significance remains unclear. In this review, we correlate structural, metamorphic and geochronological data in both terranes and parts of their bounding cratons, and suggest that the Ruker Terrane and Rauer Group in Antarctica were continuous with the Rengali Province in India. Together with the established correlation between the EGP and the Rayner Complex, this implies that cratonic India along with the EGP-Rayner amalgam collided with the Archaean Ruker Terrane (part of the Crohn craton) at ∼520 Ma along the southern Prince Charles Mountain in East Antarctica. This suture is distinct from the Grenvillian suture between EGP-Rayner and cratonic India.
Otavi Group is a 1.5−3.5-km-thick epicontinental marine carbonate succession of
Neoproterozoic age, exposed in an 800-km-long Ediacaran−Cambrian fold belt that rims
the SW cape of Congo craton in northern Namibia. Along its southern margin, a contiguous
distally tapered foreslope carbonate wedge of the same age is called Swakop Group.
Swakop Group also occurs on the western cratonic margin, where a crustal-scale thrust
cuts out the facies transition to the platformal Otavi Group.
Subsidence accommodating Otavi Group resulted from S−N crustal stretching (770−655
Ma), followed by post-rift thermal subsidence (655−600 Ma). Rifting under southern
Swakop Group continued until 650−635 Ma, culminating with breakup and a S-facing
continental margin. No hint of a western margin is evident in Otavi Group, suggesting a
transform margin to the west, kinematically consistent with S−N plate divergence. Rift related
peralkaline igneous activity in southern Swakop Group occurred around 760 and
746 Ma, with several rift-related igneous centres undated. By comparison, western Swakop
Group is impoverished in rift-related igneous rocks.
Despite low paleoelevation and paleolatitude, Otavi and Swakop groups are everywhere
imprinted by early and late Cryogenian glaciations, enabling unequivocal stratigraphic
division into five epochs (period divisions): (1) non-glacial late Tonian, 770−717 Ma; (2)
glacial early Cryogenian/Sturtian, 717−661 Ma; (3) non-glacial middle Cryogenian,
661−646±5 Ma; (4) glacial late Cryogenian/Marinoan, 646±5−635 Ma; and (5) non-glacial
early Ediacaran, 635−600±5 Ma. Odd numbered epochs lack evident glacioeustatic
fluctuation; even numbered ones were the Sturtian and Marinoan snowball Earths. This
study aimed to deconstruct the carbonate succession for insights on the nature of
Cryogenian glaciations. It focuses on the well-exposed southwestern apex of the arcuate
fold belt, incorporating 585 measured sections (totaling >190 km of strata) and >8,764
pairs of δ13C/δ18Ocarb analyses (tabulated in Supplementary On-line Information).
Each glaciation began and ended abruptly, and each was followed by anomalously thick
‘catch-up’ depositional sequences that filled accommodation space created by synglacial
tectonic subsidence accompanied by very low average rates of sediment accumulation. Net
subsidence was 38% larger on average for the younger glaciation, despite its 3.5−9.3-times
shorter duration. Average accumulation rates were subequal, 4.0 vs 3.3−8.8 m Myr−1,
despite syn-rift tectonics and topography during Sturtian glaciation, versus passive-margin
subsidence during Marinoan. Sturtian deposits everywhere overlie an erosional
disconformity or unconformity, with depocenters ≤1.6 km thick localized in subglacial rift
basins, glacially carved bedrock troughs and moraine-like buildups. Sturtian deposits are
dominated by massive diamictite, and the associated fine-grained laminated sediments
appear to be local subglacial meltwater deposits, including a deep subglacial rift basin. No
marine ice-grounding line is required in the 110 Sturtian measured sections in our survey.
In contrast, the newly-opened southern foreslope was occupied by a Marinoan marine
ice grounding zone, which became the dominant repository for glacial debris eroded from
the upper foreslope and broad shallow troughs on the Otavi Group platform, which was
glaciated but left nearly devoid of glacial deposits. On the distal foreslope, a distinct
glacioeustatic falling-stand carbonate wedge is truncated upslope by a glacial
disconformity that underlies the main lowstand grounding-zone wedge, which includes a
proximal 0.60-km-high grounding-line moraine. Marinoan deposits are recessional overall,
since all but the most distal overlie a glacial disconformity. The Marinoan glacial record is
that of an early ice maximum and subsequent slow recession and aggradation, due to
tectonic subsidence. Terminal deglaciation is recorded by a ferruginous drape of stratified
diamictite, choked with ice-rafted debris, abruptly followed by a syndeglacial-postglacial
cap-carbonate depositional sequence. Unlike its Sturtian counterpart, the post-Marinoan
sequence has a well-developed basal transgressive (i.e., deepening-upward) cap dolomite
(16.9 m regional average thickness, n=140) with idiosyncratic sedimentary features
including sheet-crack marine cements, tubestone stromatolites and giant wave ripples. The
overlying deeper-water calci-rhythmite includes crystal-fans of former aragonite benthic
cement ≤90 m thick, localized in areas of steep sea-floor topography. Marinoan sequence
stratigraphy is laid out over ≥0.6 km of paleobathymetric relief.
Late Tonian shallow-neritic δ13Ccarb records were obtained from the 0.4-km-thick
Devede Fm (~770−760 Ma) in Otavi Group and the 0.7-km-thick Ugab Subgroup
(~737−717 Ma) in Swakop Group. Devede Fm is isotopically heavy, +4−8‰ VPDB, and
could be correlative with Backlundtoppen Fm (NE Svalbard). Ugab Subgroup post-dates
746 Ma volcanics and shows two negative excursions bridged by heavy δ13C values. The
negative excursions could be correlative with Russøya and Garvellach CIEs (carbon isotope
excursions) in NE Laurentia.
Middle Cryogenian neritic δ13C records from Otavi Group inner platform feature two
heavy plateaus bracketed by three negative excursions, correlated with Twitya (NW
Canada), Taishir (Mongolia) and Trezona (South Australia) CIEs. The same pattern is
observed in carbonate turbidites in distal Swakop Group, with the sub-Marinoan falling stand
wedge hosting the Trezona CIE recovery. Proximal Swakop Group strata equivalent
to Taishir CIE and its subsequent heavy plateau are shifted bidirectionally to uniform
values of +3.0−3.5‰.
Early Ediacaran neritic δ13C records from Otavi Group inner platform display a deep
negative excursion associated with the post-Marinoan depositional sequence and heavy
values (≤+11‰) with extreme point-to-point variability (≤10‰) in the youngest Otavi
Group formation. Distal Swakop Group mimics older parts of the early Ediacaran inner
platform δ13C records, but after the post-Marinoan negative excursion, proximal Swakop
Group values are shifted bidirectionally to +0.9±1.5‰. Destruction of positive and negative
CIEs in proximal Swakop Group is tentatively attributed to early seawater-buffered
diagenesis (dolomitization), driven by geothermal porewater convection that sucks
seawater into the proximal foreslope of the platform. This hypothesis provocatively implies
that CIEs originating in epi-platform waters and shed far downslope as turbidites are
decoupled from open-ocean DIC (dissolved inorganic carbon), which is recorded by the
altered proximal Swakop Group values closer to DIC of modern seawater.
Carbonate sedimentation ended when the cratonic margins collided with and were
overridden by the Atlantic coast-normal Northern Damara and coast-parallel Kaoko
orogens at 0.60−0.58 Ga. A forebulge disconformity separates Otavi/Swakop Group from
overlying foredeep clastics. In the cratonic cusp, where the orogens meet at a right angle,
the forebulge disconformity has an astounding ≥1.85 km of megakarstic relief, and kmthick
mass slides were displaced gravitationally toward both trenches, prior to orogenic
shortening responsible for the craton-rimming fold belt.
The Ediacaran–Cambrian transition was a time of profound reorganisation of the biosphere, coinciding with the assembly of Gondwana and increasing atmospheric and oceanic oxygenation. The lower Cambrian marine sediments of the Stansbury Basin, South Australia, were deposited at low northern paleolatitudes on the western margin of the emerging Pacific Ocean. Here we report results of a multi-pronged investigation employing trace and rare earth element (REE) abundances, total organic carbon (TOC) contents and pyritic sulfur isotopic compositions (δ³⁴Spy) in carbonaceous shales from three formations within the Normanville and Kanmantoo groups (sequences Є1.2 to Є2.2). TOC ranges from ≤0.5 wt% in the Emu Bay Shale, through 0.4–1.9 wt% in the Talisker Formation, to 0.2–2.6 wt% in the Heatherdale Shale. Covariance is demonstrated between trace elements and organic matter, with comparative uranium enrichment in the Heatherdale Shale likely linked to increased primary productivity. Heavy REEs and yttrium are typically more depleted than light REEs. Provenance appears to evolve through the upper Normanville sediments into the Kanmantoo Group, corroborating published detrital zircon interpretations that suggest an increasing dominance of southerly derived sources. The prevailing paleoredox regime for the Heatherdale Shale and the Talisker Formation was dysoxic, evolving into progressively more reducing conditions up section, the latter exhibiting a secular decline in δ³⁴Spy (from +10 to −11‰ VCDT). Conversely, redox proxies concur in demonstrating that the basal fossiliferous Emu Bay Shale accumulated beneath an oxic water column. Comparison of trace element and REE distributions with those of slightly older sequences on the Yangtze Platform, South China, reveals striking similarities, implying that the trace element chemistry of the Paleo-Pacific and Asian oceans was homogeneous.
• KEY POINTS
• Trace and rare earth element, total organic carbon and sulfur isotopic data provide a multi-faceted profile of shales from three formations in the Stansbury Basin.
• The prevailing paleoredox regime for the Heatherdale Shale and Talisker Formation was dysoxic, whereas the basal Emu Bay Shale accumulated beneath an oxic water column.
• The strong covariance between TOC and normalised Mo, V and U in these shales highlights the evolving bioproductivity and oxygenation of the early Cambrian ocean.
• Similar element signatures in lower Cambrian black shales, South China, reflect the homogeneous biogeochemistry of the Paleo-Pacific and Asian oceans.
Madagascar hosts several Paleoproterozoic sedimentary sequences that are key to unraveling the geodynamic evolution of past supercontinents on Earth. New detrital zircon U–Pb and Hf data, and a substantial new database of ∼15,000 analyses are used here to compare and contrast sedimentary sequences in Madagascar, Africa, and India. The Itremo Group in central Madagascar, the Sahantaha Group in northern Madagascar, the Maha Group in eastern Madagascar, and the Ambatolampy Group in central Madagascar have indistinguishable age and isotopic characteristics. These samples have maximum depositional ages >1700 Ma, with major zircon age peaks at c. 2500 Ma, c. 2000 Ma, and c. 1850 Ma. We name this the Greater Itremo Basin, which covered a vast area of Madagascar in the late Paleoproterozoic. These samples are also compared with those from the Tanzania and the Congo cratons of Africa, and the Dharwar Craton and Southern Granulite Terrane of India. We show that the Greater Itremo Basin and sedimentary sequences in the Tanzania Craton of Africa are correlatives. These also tentatively correlate with sedimentary protoliths in the Southern Granulite Terrane of India, which together formed a major intra‐Nuna/Columbia sedimentary basin that we name the Itremo‐Muva‐Pandyan Basin. A new Paleoproterozoic plate tectonic configuration is proposed where central Madagascar is contiguous with the Tanzania Craton to the west and the Southern Granulite Terrane to the east. This model strongly supports an ancient Proterozoic origin for central Madagascar and a position adjacent to the Tanzania Craton of East Africa.
Neoproterozoic tectonic geography was dominated by the formation of the supercontinent Rodinia, its break-up and the subsequent amalgamation of Gondwana. The Neoproterozoic was a tumultuous time of Earth's history, with large climatic variations, the emergence of complex life and a series of continent-building orogenies of a scale not repeated until the Cenozoic. Here we synthesise available geological and palaeomagnetic data and build the first full-plate, topological model of the Neoproterozoic that maps the evolution of the tectonic plate configurations during this time. Topological models trace evolving plate boundaries and facilitate the evaluation of " plate tectonic rules " such as subduction zone migration through time when building plate models. There is a rich history of subduction zone proxies preserved in the Neoproterozoic geological record, providing good evidence for the existence of continental and intra-oceanic subduction zones through time. These are preserved either as volcanic arc protoliths accreted in continent-continent, or continent-arc, collisions, or as the detritus of these volcanic arcs preserved in successor basins. Despite this, we find that the model presented here only predicts, on average, ~90% of the total length of subduction active today, suggesting that we have produced a conservative model and are likely underestimating the amount of subduction, either due to a simplification of tectonically complex areas, or because of the absence of preservation in the geological record (e.g. ocean-ocean convergence). Furthermore, the reconstruction of plate boundary geometries provides constraints for global-scale earth system parameters, such as the role of volcanism or ridge production on the planet’s icehouse climatic excursion during the Cryogenian. Besides modelling plate boundaries, our model presents some notable departures from previous Rodinia models. We omit India and South China from Rodinia completely, due to long-lived subduction preserved on margins of India and conflicting palaeomagnetic data for the Cryogenian, such that these two cratons act as ‘lonely wanderers’ for much of the Neoproterozoic. We also introduce a Tonian-Cryogenian aged rotation of the Congo-São Francisco Craton relative to Rodinia to better fit palaeomagnetic data and account for thick passive margin sediments along its southern margin during the Tonian. The GPlates files of the model are released to the public and it is our expectation that this model can act as a foundation for future model refinements, the testing of alternative models, as well as providing constraints for both geodynamic and palaeoclimate models.
The Southern Granulite terrane, southern India, comprises a vast exposure of deep crust and forms a key region in the reconstruction of the Gondwana supercontinent. An E-W-trending crustal-scale shear zone, the Palghat-Cauvery suture zone system, which formed during the late Neoproterozoic-Cambrian (0.75-0.50 Ga), marks a prominent terrane boundary separating terranes with a predominantly late Neoarchean (ca. 2.5 Ga) regional granulite metamorphism to the north from those with an Ediacaran-Cambrian (0.63-0.50 Ga) regional granulite metamorphism to the south. Focusing on the younger granulite metamorphic domains, we present here new zircon U-Pb ages and Hf isotopic compositions for 11 charnockite orthogneisses from the Madurai, Trivandrum, and Nagercoil blocks and contribute to the resolution of the age of their magmatic protoliths. This study shows that the charnockite orthogneisses south of the Palghat-Cauvery suture zone relate to a minimum of four distinct episodes of felsic magmatism centered at: Ca. 2.62-2.46 Ga, ca. 2.05-1.84 Ga, ca. 1.0- 0.9 Ga, and ca. 0.80-0.76 Ga, pertaining to the Siderian, Orosirian, and Tonian Periods. Hafnium isotope analyses of zircon grains from the charnockite gneisses suggest that the protoliths of the ca. 2.05-1.98 Ga gneisses from the Trivandrum and Nagercoil blocks and the ca. 1.0-0.9 Ga gneisses along the southeastern Madurai block involved a significant juvenile magma component, while the protoliths of charnockite gneisses elsewhere in the Madurai block formed mainly through recycling of older crust up to ca. 3.2 Ga. A regional granulite-facies metamorphic imprint during the Ediacaran-Cambrian marked an advanced stage in the amalgamation of the Madurai, Trivandrum, and Nagercoil blocks into the East African orogen and its collision with the Dharwar craton.
Granulites of the southern East African Orogen formed by continental collision during Gondwana assembly. The highest metamorphic gradients of 25–50 °C km−1 were attained at 0.58–0.53 Ga in a microcontinental block that was sandwiched between two collisional sutures and is now exposed in Madagascar and southern India. The 50 Myr duration of extreme pressure–temperature (P–T) conditions and lack of coeval mantle magmatism suggest that metamorphism was driven by radiogenic heat accumulation beneath a long–lived orogenic plateau. Bounding sutures most likely record transfer of this microcontinent across the Neoproterozoic Mozambique Ocean, analogous to Gondwanan terranes that crossed Tethys before final India–Asia collision and, like Tibet, these sutures mark the edges of a plateau that formed following terminal ocean closure and collision. Both sutures record moderate metamorphic gradients of 15–25 °C km−1 but with quite different ages. Metamorphism along the western suture at 0.65–0.61 Ga followed the end of magmatism in an adjacent 0.85–0.65 Ga ocean–arc terrane. It has an anti–clockwise P–T path that reflects preferential thickening of the hot arc during early stages of collision, and dates ocean closure at the western suture. Metamorphism along the eastern suture at 0.53–0.51 Ga has a clockwise P–T path and is widely assumed to date terminal collision in the East African Orogen. However, this event was coeval with rapid exhumation of granulites in the adjacent plateau and is more likely to reflect reactivation of a much older eastern suture during plateau collapse. Great care should be taken when using metamorphism to date ocean closure in ancient orogens. Rocks with hot metamorphic gradients give poor age constraints on initial collision because peak T is attained >50 Myr after ocean closure if radioactivity is a major part of the heat budget. Suture zone rocks with moderate metamorphic gradients can provide more reliable estimates for the time of ocean closure but are also prone to later reactivation in orogens with protracted histories.
Precambrian supercontinents Nuna-Columbia (1.7 to 1.3 billion years ago) and Rodinia (1.1 to 0.7 billion years ago) have been proposed. However, the arrangements of crustal blocks within these supercontinents are poorly known. Huge, dominantly basaltic magmatic outpourings and intrusions, covering up to millions of square kilometres, termed Large Igneous Provinces, typically accompany (super) continent breakup, or attempted breakup and offer an important tool for reconstructing supercontinents. Here we focus on the Large Igneous Province record for Siberia and Laurentia, whose relative position in Nuna-Columbia and Rodinia reconstructions is highly controversial. We present precise geochronology - nine U-Pb and six Ar-Ar ages - on dolerite dykes and sills, along with existing dates from the literature, that constrain the timing of emplacement of Large Igneous Province magmatism in southern Siberia and northern Laurentia between 1,900 and 720 million years ago. We identify four robust age matches between the continents 1,870, 1,750, 1,350 and 720 million years ago, as well as several additional approximate age correlations that indicate southern Siberia and northern Laurentia were probably near neighbours for this 1.2-billion-year interval. Our reconstructions provide a framework for evaluating the shared geological, tectonic and metallogenic histories of these continental blocks.
Prior to the Grenvillian continentcontinent collision at about 1.0 Ga, the southern margin of Laurentia was a long-lived convergent margin that extended from Greenland to southern California. The truncation of these 1.8-1.0 Ga orogenic belts in southwestern and northeastern Laurentia suggests that they once extended farther. We propose that Australia contains the continuation of these belts to the southwest and that Baltica was the continuation to the northeast. The combined orogenic system was comparable in length to the modern American Cordilleran or Alpine-Himalayan systems. This plate reconstruction of the Proterozoic supercontinent Rodinia called AUSWUS (Australia-Southwest U.S.) differs from the well-known SWEAT (Southwest U.S.-East Antarctic) reconstruction in that Australia, rather than northern Canada, is adjacent to the southwestern United States. The AUSWUS reconstruction is supported by a distinctive "fingerprint" of geologic similarities and tectonic histories between Australia and the southwestern United States from 1.8 to 0.8 Ga, and by a better agreement between 1.45 and 1.0 Ga paleomagnetic poles for Australia and Laurentia.
We report paleomagnetic and geochronologic results from two Late Proterozoic mafic dikes exposed in Archean-cored uplifts from northwestern Wyoming and 40Ar/39Ar results from a gabbro sill that intrudes lower sedimentary strata of the Belt Supergroup in western Montana. The gabbro sill yields a 40Ar/39Ar plateau date of 776 Ma that records the age of sill emplacement during Late Proterozoic time. Paleomagnetic results from the mafic dike at Mount Moran, Teton Range, and the Christmas Lake dike, Beartooth Mountains, indicate magentizations with similar directions and virtual geomagnetic poles (GVP's), which we interpret to be primary thermoremanent magnetizations acquired during dike emplacement and cooling. A hornblende from the Christmas Lake dike yields a 40Ar/39Ar plateau date of 774 Ma, which is statistically identical to that of the gabbro sill from western Montana. The similarity of the dike site-mean directions and VGP's suggest that their magentizations are of similar age. 40Ar/39Ar results from a hornblende-pyroxene concentrate from the Mount Moran dike are discordant and contain excess 40; a precise estimate of the age of this sample is not possible given our data, but the paleomagnetic and geochronologic results suggest that it is of the Late Proterozoic age, and not Middle Proterozoic as previously argued. The VGP's from the Mount Moran and Christmas Lake Dikes are similar to those of identical age from southwestern Montana and northern and western Canada. These mafic dikes and sills are part of a regional magmatic event that affected the western part of the Laurentian craton at about 780 Ma.
Open-access digital resources: http://www.earthbyte.org/ocean-basin-evolution-and-global-scale-plate-reorganization-events-since-pangea-breakup/
ftp://ftp.earthbyte.org/Data_Collections/Muller_etal_2016_AREPS
We present a revised global plate motion model with continuously closing plate boundaries ranging from the Triassic at 230 Ma to the present day, assess differences between alternative absolute plate motion models, and review global tectonic events. Relatively high mean absolute plate motion rates around 9–10 cm yr-1 between 140 and 120 Ma may be related to transient plate motion accelerations driven by the successive emplacement of a sequence of large igneous provinces during that time. A ~100 Ma event is most clearly expressed in the Indian Ocean and may reflect the initiation of Andean-style subduction along southern continental Eurasia, while an ~80 Ma acceleration of mean rates from 6 to 8 cm yr-1 reflects the initial northward acceleration of India and simultaneous speedups of plates in the Pacific. An event at ~50 Ma expressed in relative, and some absolute plate motion changes around the globe and in a reduction of global mean velocities from about 6 to 4–5 cm yr-1, indicates that an increase in collisional forces (such as the India-Eurasia collision) and ridge subduction events in the Pacific (such as the Izanagi-Pacific Ridge) play a significant role in modulating plate velocities.
The tectonics, dynamics, and biogeographic landscape of the early Paleozoic were dominated by the opening and expansion of one large ocean-the Rheic-and the diminution to terminal closure of another-Iapetus. An understanding of the evolution of these oceans is thus central to an understanding of the early Paleozoic, but their chronicle also presents a rich temporal profile of the Wilson cycle, illustrating continental-scale rifting, microcontinent formation, ocean basin development, arc accretion, and continent-continent collision. Nevertheless, contemporary paleogeographic models of the Iapetus and Rheic oceans remain mostly schematic or spatiotemporally disjointed, which limits their utility and hinders their testing. Moreover, many of the important kinematic and dynamic aspects of the evolution of these oceans are impossible to unambiguously resolve from a conceptual perspective and the existing models unsurprisingly present a host of contradictory scenarios. With the specific aim to resolve some of the uncertainties in the evolution of this early Paleozoic domain, and a broader aim to instigate the application of quantitative kinematic models to the early Paleozoic, I present a new plate tectonic model for the Iapetus and Rheic oceans. The model has realistic tectonic plates, which include oceanic lithosphere, that are defined by explicit and rigorously managed plate boundaries, the nature and kinematics of which are derived from geological evidence and plate tectonic principles. Accompanying the presentation and discussion of the plate model, an extensive review of the underlying geological and paleogeographic data is also presented.
Most recent paleogeographic reconstructions of the supercontinent Nuna juxtapose the North Australian craton, Mawson continent (South Australia–East Antarctica), and Laurentia between 1.6 Ga and 1.3 Ga but differ in their relative positioning. The >10-km-thick siliciclastic Rocky Cape Group of Tasmania was deposited in an opening marine basin on the margin of East Antarctica during Nuna breakup. Based on a similar detrital zircon signature and depositional age, the Rocky Cape Group has been correlated with the upper Belt-Purcell Supergroup in Laurentia, thus representing a key tie point within Nuna. Here the detrital zircon age signature of Mesoproterozoic Rocky Cape Group quartzites is investigated by comparing new detrital zircon U-Pb-Hf isotopic data to an extensive compilation of zircon isotopic data from Australia, East Antarctica, and Laurentia. Our analysis demonstrates that the Rocky Cape Group is unlikely to have been sourced from any geological terrane exposed in present-day Australia. Instead, zircon U-Pb-Hf isotopic data from basement terranes in Laurentia and East Antarctica show striking similarities to the Rocky Cape Group detrital signature. Paleo-current data indicate that the majority of sediment in the Rocky Cape Group was sourced from Laurentia, which was to the southeast (present-day coordinates) of Tasmania, supporting a SWEAT-like (southwest United States–East Antarctica) configuration for Nuna. We suggest that rifting left a thinned continental connection between East Antarctica and Laurentia onto which the lower-middle Rocky Cape Group was deposited between 1.45 and 1.30 Ga.
Oceanic fracture zone traces are widely used in studies of seafloor morphology and plate kinematics. Satellite altimetry missions have resulted in high-resolution gravity maps in which all major fracture zones and other tectonic fabric can be identified, and numerous scientists have digitized such lineaments. We have initiated a community effort to maintain low-cost infrastructure that allows seafloor fabric lineaments to be stored, accessed and updated. A key improvement over past efforts is our processing software (released as a GMT5 supplement) that allows for semi-automatic corrections to previously digitized fracture zone traces given improved gridded data sets. Here we report on our seafloor fabric processing tools, which complement our database of seafloor fabric lineations, magnetic anomaly identifications and plate kinematic models.
Before its collision with Eurasia(1-5), the Indian Plate moved rapidly, at rates exceeding 140 mm yr(-1) for a period of 20 million years(1,3-7). This motion is 50 to 100% faster than the maximum sustained rate of convergence of the main tectonic plates today(8). The cause of such high rates of convergence is unclear and not reproduced by numerical models(9,10). Here we show that existing geological data(11,12) support the existence of two, almost parallel, northward dipping subduction zones between the Indian and Eurasian plates, during the Early Cretaceous period. We use a quantitative model to show that the combined pull of two subducting slabs can generate anomalously rapid convergence between India and Eurasia. Furthermore, in our simulations a reduction in length of the southern subduction system, from about 10,000 to 3,000 km between 90 and 80 million years ago, reduced the viscous pressure between the subducting slabs and created a threefold increase in plate convergence rate between 80 and 65 million years ago. Rapid convergence ended 50 million years ago, when the Indian Plate collided with the southern subduction system. Collision of India with Eurasia and the northern subduction system had little effect on plate convergence rates before 40 million years ago. We conclude that the number and geometry of subduction systems has a strong influence on plate migration rates.
Previous paleomagnetic work has appeared to demand the breakup of southwest United States−East Antarctic (SWEAT) type Rodinia reconstructions before ca. 750 Ma, significantly earlier than the stratigraphic record of rift-drift transition between 715 Ma and 650 Ma. Here we reanalyze Australian paleomagnetic and regional tectonic data to produce a model in which the Precambrian Australian continent had a slightly different configuration before the breakup of Rodinia. A cross-continental megashear zone developed along the Paterson and Petermann orogens at ca. 650–550 Ma, during or after the breakup of Rodinia, manifested as an ∼40° clockwise rotation of the South and West Australian cratons relative to the North Australian craton around a vertical axis in Central Australia. This model reconciles major paleomagnetic discrepancies within Australia, and allows for a longer lifespan of SWEAT-like reconstructions of Rodinia that are consistent with the Neoproterozoic stratigraphic records of Australia and Laurentia.
From the formation of Rodinia at the end of the Mesoproterozoic to the commencement of Pangea breakup at the end of the Paleozoic, the South China craton first formed and then occupied a position adjacent to Western Australia and northern India. Early Neoproterozoic suprasubduction zone magmatic arc-backarc assemblages in the craton range in age from ca. 1000 Ma to 820 Ma and display a sequential northwest decrease in age. These relations suggest formation and closure of arc systems through southeast-directed subduction, resulting in progressive northwestward accretion onto the periphery of an already assembled Rodinia. Siliciclastic units within an early Paleozoic succession that transgresses across the craton were derived from the southeast and include detritus from beyond the current limits of the craton. Detrital zircon age spectra require an East Gondwana source and are very similar to the Tethyan Himalaya and younger Paleozoic successions from Western Australia, suggesting derivation from a common source and by inference accumulation in linked basins along the northern margin of Gondwana, a situation that continued until rifting and breakup of the craton in the late Paleozoic.
Earth's middle age, extending from 1.7 to 0.75 Ga, was characterized by environmental, evolutionary, and lithospheric stability that contrasts with the dramatic changes in preceding and succeeding eras. The period is marked by a paucity of preserved passive margins, an absence of a significant Sr anomaly in the paleoseawater record and in the epsilon(Hf(t)) in detrital zircon, a lack of orogenic gold and volcanic-osted massive sulfide deposits, and an absence of glacial deposits and iron formations. In contrast, anorthosites and kindred bodies are well developed and major pulses of Mo and Cu mineralization, including the world's largest examples of these deposits, are features of this period. These trends are attributed to a relatively stable continental assemblage that was initiated during assembly of the Nuna supercontinent by ca. 1.7 Ga and continued until breakup of its closely related successor, Rodinia, ca. 0.75 Ga. The overall low abundance of passive margins is consistent with a stable continental configuration, which also provided a framework for environmental and evolutionary stability. A series of convergent margin accretionary orogens developed along the edge of the supercontinent. Abundant anorthosites and related rocks developed inboard of the plate margin. Their temporal distribution appears to link with the secular cooling of the mantle, at which time the overlying continental lithosphere was strong enough to be thickened and to support the emplacement of large plutons into the crust, yet the underlying mantle was still warm enough to result in widespread melting of the lower thickened crust.
A reorganization centered on the Pacific plate occurred ~53-47 million years ago. A ‘top-down’ plate tectonic mechanism, complete subduction of the Izanagi plate, as opposed to a ‘bottom-up’ mantle flow mechanism, has been proposed as the main driver. Verification based on marine geophysical observations is impossible as most ocean crust recording this event has been subducted. Using a forward modeling approach, which assimilates surface plate velocities and shallow thermal structure of slabs into mantle flow models, we show that complete Izanagi plate subduction and margin-wide slab detachment induced a major change in sub-Pacific mantle flow, from dominantly southward before 60 M to north-northeastward after 50 Ma. Our results agree with onshore geology, mantle tomography, and the inferred motion of the Hawaiian hotspot and are consistent with a plate-tectonic process driving the rapid plate-mantle reorganization in the Pacific hemisphere between 60 and 50 Ma, as reflected in tectonic changes in the Pacific and surrounding ocean basins.
Since 2007/08, seismographs were deployed in many new locations across much of Antarctica. Using the records from 122 broadband seismic stations, over 10,000 Rayleigh wave fundamental-mode dispersion curves have been retrieved from earthquake waveforms and from ambient noise. Using the processed dataset, a 3-D S-velocity model for the Antarctic lithosphere was constructed using a single-step surface-wave tomographic method, and a Moho depth map was estimated from the model. Using the derived crustal thicknesses, the average ratio of lithospheric-mantle and crustal densities of Antarctica was calculated. The calculated density ratio indicates that the average crustal density for Antarctica is much higher than average values for continental crust, or the average density of lithospheric mantle is so low as to be equal to low density bound of Archean lithosphere. The latter implies that the lithospheric mantle in much of Antarctica should be old and of Archean age. The East Antarctic Mountain Ranges (EAMOR) represent a thick crustal belt, with the thickest crust (~60 km) located close to Dome A. Very high velocities can be found at depths greater than 200 km beneath parts of East Antarctica, demonstrating that the continental lithosphere extends deeper than 200 km. The very thick crust beneath the EAMOR may represent the collision suture of East Gondwana with Indo-Antarctica and West Gondwana during the Pan-African Orogeny.
We present a revised interpretation of magnetic anomalies and fracture zones on the Southwest Indian Ridge (SWIR; Africa-Antarctica) and the Southeast Indian Ridge (SEIR; Capricorn-Antarctica) and use them to calculate 2-plate finite rotations for anomalies 34 to 20 (84 to 43 Ma). Central Indian Ridge (CIR; Capricorn-Africa) rotations are calculated by summing the SWIR and SEIR rotations. These rotations provide a high-resolution record of changes in the motion of India and Africa at the time of the onset of the Reunion plume head. An analysis of the relative velocities of India, Africa and Antarctica leads to a refinement of previous observations that the speedup of India relative to the mantle was accompanied by a slowdown of Africa. The most rapid slowdown of Africa occurs around Chron 32Ay (71 Ma), the time when India's motion relative to Africa notably starts to accelerate. Using the most recent Geomagnetic Polarity Timescale (GTS12) we show that India's velocity relative to Africa was characterized by an acceleration from roughly 60 to 180 mm yr-1 between 71 and 66 Ma, a short pulse of superfast motion (̃180 mm yr-1) between 66 and 63 Ma, an abrupt slowdown to 120 mm yr-1 between 63 and 62 Ma, and then a long period (63 to 47 Ma) of gradual slowing, but still fast motion (̃100 mm yr-1), which ends with a rapid slowdown after Chron 21o (47 Ma). Changes in the velocities of Africa and India with respect to the mantle follow a similar pattern. The fastest motion of India relative to the mantle, ̃220 mm yr-1, occurs during Chron 29R. The SWIR rotations constrain three significant changes in the migration path of the Africa-Antarctic stage poles: following Chron 33y (73 Ma), following Chron 31y (68 Ma), and following Chron 24o (54 Ma). The change in the migration path of the SWIR stage poles following Chron 33y is coincident with the most rapid slowdown in Africa's motion. The change in the migration path after Chron 31y, although coincident with the most rapid acceleration of India's northward motion, may be related to changes in ridge push forces on the SWIR associated with the onset of extension along the Bain transform fault zone. The initial slowdown in India's motion relative to Africa between 63 and 62 Ma is more abrupt than predictions based on published plume head force models, suggesting it might have been caused by a change in plate boundary forces. The abrupt change in the migration path of the SWIR stage poles after Chron 24o is not associated with major changes in the velocities of either Africa or India and may reflect Atlantic basin plate motion changes associated with the arrival at the Earth's surface of the Iceland plume head. The abruptness of India's slowdown after Chron 21o is consistent with a collision event.
Plate tectonics, our major paradigm for how the Earth works, was established in the 1960ies following decades of observational research that culminated in key discoveries such as geomagnetic reversals, mid-ocean ridges, transform faults, and seafloor spreading. Plate tectonics is the surface manifestation of mantle convection, but the large contrast in viscosities between the lithosphere and the deeper mantle leads to departures from a simple boiling pot analogy. We review seafloor morphology, the methodologies of relative and absolute plate motion reconstructions, the plate driving forces believed responsible, and challenges that must be overcome to make new progress in the above areas.
U–Pb baddeleyite ages and paleomagnetic poles obtained for dykes on Devon Island and Ellesmere Island in the Canadian Arctic and the Thule region of Greenland show that they are associated with the Franklin magmatic event. This study is the only one devoted to Franklin igneous rocks where a primary paleomagnetic remanence and U–Pb age have been obtained from the same rocks. Ages from this study range from 721 to 712 Ma, but paleomagnetic directional data show no clear age progression. The paleomagnetic poles from each of the two regional subsets are significantly different at the 95% confidence level from paleomagnetic results previously published for the Franklin event in the Canadian Shield. The difference in the pole locations can be accounted for, to first approximation, by a simple model of early Cenozoic block rotations among the North American plate, Greenland, and a hypothesized ancient microplate comprising Ellesmere, Devon, Cornwallis, and perhaps Somerset islands. A new grand-mean paleopole for the Franklin event, including restoration of Greenland and the proposed “Ellesmere microplate” to North America, is located at (8.4°N, 163.8°E, A95 = 2.8°, N = 78 sites) and is a key pole for Neoproterozoic supercontinent reconstructions.Des âges U–Pb, déterminés sur de la baddeleyite, et des pôles paléomagnétiques obtenus de dykes des îles de Devon et d’Ellesmere, dans l’Arctique canadien, et de la région de Thulé au Groenland, montrent que ces dykes sont associés à l’événement magmatique de Franklin. La présente étude est la seule consacrée aux roches ignées de Franklin où une rémanence paléomagnétique primaire et des âges U–Pb ont été obtenus des mêmes roches. Les âges dans cette étude varient de 721 à 712 Ma, mais les données sur les directions paléomagnétiques ne montrent aucune progression claire de l’âge. Les pôles paléomagnétiques de chacun des deux sous-ensembles régionaux diffèrent de manière significative, au niveau de confiance 95%, des résultats paléomagnétiques publiés antérieurement pour l’événement de Franklin dans le Bouclier canadien. La différence d’emplacement des pôles peut être expliquée, en une première approximation, par un modèle simple de rotations de blocs, au Cénozoïque précoce, entre la plaque Nord-américaine, le Groenland et une ancienne plaque hypothétique qui comprenait les îles d’Ellesmere, de Devon, de Cornwallis et peut-être de Somerset. Un nouveau paléopôle de grande moyenne pour l’événement Franklin, incluant la restoration du Groenland et de la «micro-plaque d’Ellesmere» proposée à l’Amérique du Nord, est situé à (8,4°N, 163,8°E, A95 = 2,8°, N = 78 sites) et constitue le pôle clé pour les reconstructions du super continent au Néoprotérozoïque.
Stratigraphic, geochronologic, and geochemical patterns of Neoproterozoic to Cambrian sedimentary and volcanic rocks in Utah, Nevada, and SE Idaho record a dynamically evolving landscape along the North American Cordillera margin, which included: (1) initial development of intracratonic basins with deposition of siliciclastic strata of the Uinta Mountain Group from ~ 770–740 Ma; (2) early rifting and volcanism along a N-S (present day geographic coordinates) basin system with deposition of diamictite-bearing strata of the Perry Canyon and related formations from ~ 720–660 Ma; (3) early, broad subsidence with deposition of mature siliciclastic strata of the lower Brigham and McCoy Creek groups from ~ 660–580 Ma; (4) final rifting, volcanism, and transition to drift with deposition of variably immature siliciclastic strata of the Prospect Mountain and correlative formations from ~ 570–520 Ma; and (5) regional subsidence along a passive margin with deposition of Middle Cambrian to Devonian carbonate-rich strata. The Uinta Mountain Group comprises fluvial to marine, feldspathic to quartzose sandstone, conglomerate, and mudstone, with detrital zircon (DZ) patterns recording a mix of local basement sources to the N and distal Laurentian sources to the SE. The lower Perry Canyon and related formations contain variably feldspathic sandstone, quartz-pebble diamictite deposited during an older glacial episode, and mudstone, with DZ patterns recording a mix of distal sources, local basement sources, and sediment recycling during early rifting. The upper Perry Canyon and related formations contain mafic volcanic rocks, polymict diamictite deposited during a younger glacial episode, volcaniclastic wacke, and mudstone, with DZ patterns recording local basement sources along an evolving rift margin and felsic volcanism from ~ 700–670 Ma. Mafic volcanic rocks and trachyte to rhyolite clasts in diamictite have geochemical signatures typical of continental rifting. The lower Brigham and McCoy Creek groups contain mostly mature quartz arenite deposited in shallow marine environments, with DZ patterns recording distal Laurentian sources. The base of the Prospect Mountain and correlative formations is marked by an influx of feldspathic, coarse-grained sediment derived from local basement sources and ~ 570-540 Ma basalt volcanism, which was followed by deposition of subfeldspathic strata with dominant 1.7–1.8 Ga DZ grains, recording sources from the SE rift margin and a marked decrease in distal sources during uplift of the Transcontinental Arch. Overlying carbonate-rich strata were deposited in shallow marine settings, with episodic influx of siliciclastic sediment derived from basement exposed during regressions. Stratigraphic thickness-age relations of Neoproterozoic to early Paleozoic strata are consistent with two episodes of rifting concentrated at ca. 700–670 Ma and 570–540 Ma along western Laurentia, leading to final development of a passive margin. Early rifting was incomplete with an estimated 25–40% extension of initially thick lithosphere that was weakened by igneous activity. Final rifting of previously thinned lithosphere involved an estimated 20–35% additional extension, renewed igneous activity, and thermal thinning of mantle lithosphere, with localized extension culminating in final separation along the continental margin. Stratigraphic, geochronologic, and available paleomagnetic data are consistent with linkage of western Laurentia to Australia-East Antarctica within Rodinia, followed by protracted rifting and drift during Cambrian time.
Tectonic reconstructions of Southeast Asia have given rise to numerous controversies that include the accretionary history of Sundaland and the enigmatic tectonic origin of the proto-South China Sea. We assimilate a diversity of geological and geophysical observations into a new regional plate model, coupled to a global model, to address these debates. Our approach takes into account terrane suturing and accretion histories, the location of subducted slabs imaged in mantle tomography in order to constrain the evolution of regional subduction zones, as well as plausible absolute and relative plate velocities and tectonic driving mechanisms. We propose a scenario of rifting from northern Gondwana in the latest Jurassic, driven by northward slab pull from north-dipping subduction of Tethyan crust beneath Eurasia, to detach East Java, Mangkalihat, southeast Borneo and West Sulawesi blocks that collided with a Tethyan intra-oceanic subduction zone in the mid-Cretaceous and subsequently accreted to the Sunda margin (i.e., southwest Borneo core) in the Late Cretaceous. In accounting for the evolution of plate boundaries, we propose that the Philippine Sea plate originated on the periphery of Tethyan crust forming this northward conveyor. We implement a revised model for the Tethyan intra-oceanic subduction zones to reconcile convergence rates, changes in volcanism and the obduction of ophiolites. In our model the northward margin of Greater India collides with the Kohistan–Ladakh intra-oceanic arc at ∼53 Ma, followed by continent–continent collision closing the Shyok and Indus–Tsangpo suture zones between ∼42 and 34 Ma.
We also account for the back-arc opening of the proto-South China Sea from ∼65 Ma, consistent with extension along east Asia and the formation of supra-subduction zone ophiolites presently found on the island of Mindoro. The related rifting likely detached the Semitau continental fragment from South China, which accreted to northern Borneo in the mid-Eocene, to account for the Sarawak Orogeny. Rifting then re-initiated along southeast China by 37 Ma to open the South China Sea, resulting in the complete consumption of proto-South China Sea by ∼17 Ma when the collision of the Dangerous Grounds and northern Palawan blocks with northern Borneo choked the subduction zone to result in the Sabah Orogeny and the obduction of ophiolites in Palawan and Mindoro. We conclude that the counterclockwise rotation of Borneo was accommodated by oroclinal bending consistent with paleomagnetic constraints, the curved lithospheric lineaments observed in gravity anomalies of the Java Sea and the curvature of the Cretaceous Natuna paleo-subduction zone. We complete our model by constructing a time-dependent network of topological plate boundaries and gridded paleo-ages of oceanic basins, allowing us to compare our plate model evolution to seismic tomography. In particular, slabs observed at depths shallower than ∼1000 km beneath northern Borneo and the South China Sea are likely to be remnants of the proto-South China Sea basin.
Tectonic reconstructions of Southeast Asia have given rise to numerous
controversies which include the accretionary history of Sundaland and
the enigmatic tectonic origin of the Proto South China Sea. We
assimilate a diversity of geological and geophysical observations into a
new regional plate model, coupled to a global model, to address these
debates. Our approach takes into account terrane suturing and accretion
histories, the location of subducted slabs imaged in mantle tomography
in order to constrain the opening and closure history of paleo-ocean
basins, as well as plausible absolute and relative plate velocities and
tectonic driving mechanisms. We propose a scenario of rifting from
northern Gondwana in the Late Jurassic, driven by northward slab pull,
to detach East Java, Mangkalihat, southeast Borneo and West Sulawesi
blocks that collided with a Tethyan intra-oceanic subduction zone in the
mid Cretaceous and subsequently accreted to the Sunda margin (i.e.
southwest Borneo core) in the Late Cretaceous. In accounting for the
evolution of plate boundaries, we propose that the Philippine Sea Plate
originated on the periphery of Tethyan crust forming this northward
conveyor. We implement a revised model for the Tethyan intra-oceanic
subduction zones to reconcile convergence rates, changes in volcanism
and the obduction of ophiolites. In our model the northward margin of
Greater India collides with the Kohistan-Ladakh intra-oceanic arc at
∼53 Ma, followed by continent-continent collision closing the
Shyok and Indus-Tsangpo suture zones between ∼42 and 34 Ma. We
also account for the back-arc opening of the Proto South China Sea from
∼65 Ma, consistent with extension along east Asia and the
emplacement of supra-subduction zone ophiolites presently found on the
island of Mindoro. The related rifting likely detached the Semitau
continental fragment from east China, which accreted to northern Borneo
in the mid Eocene, to account for the Sarawak Orogeny. Rifting then
re-initiated along southeast China by 37 Ma to open the South China Sea,
resulting in the complete consumption of Proto South China Sea by
∼17 Ma when the collision of the Dangerous Grounds and northern
Palawan blocks with northern Borneo choked the subduction zone to result
in the Sabah Orogeny and the obduction of ophiolites in Palawan and
Mindoro. We conclude that the counterclockwise rotation of Borneo was
accommodated by oroclinal bending consistent with paleomagnetic
constraints, the curved lithospheric lineaments observed in gravity
anomalies of the Java Sea and the curvature of the Cretaceous Natuna
paleo-subduction zone. We complete our model by constructing a
time-dependent network of continuously closing plate boundaries and
gridded paleo-ages of oceanic basins, allowing us to test our plate
model evolution against seismic tomography. In particular, slabs
observed at depths shallower than ∼1000 km beneath northern
Borneo and the South China Sea are likely to be remnants of the Proto
South China Sea basin.
Coupled U-Pb and Hf isotopic analysis of detrital zircons from metasedimentary rocks of the Southern Granulite terrane (India) provides provenance information that helps unravel their paleotectonic position before Gondwana amalgamated. The metasedimentary packages of the Salem block (southernmost extension of Dharwar craton) record a restricted juvenile late Archean to early Paleoproterozoic (2.7-2.45 Ga) source provenance and epsilon Hf values between +0.3 and +8.8. Similar late Archean juvenile crust is found throughout the Dharwar craton and represents a likely source for the Salem block metasedimentary rocks. By contrast, the metasedimentary rocks of the Madurai block (south of the Salem block) show a predominantly Archean to Paleoproterozoic provenance (3.2-1.7 Ga) in the northern part of the Madurai block and a largely late Mesoproterozoic to Neoproterozoic provenance (1.1-0.65 Ga) in the southern part of the Madurai block. Collectively, the Madurai block metasedimentary rocks record a mixture of reworked Archean and Paleoproterozoic sources, as well as juvenile Paleoproterozoic, late Mesoproterozoic, and evolved Neoproterozoic sources. These detrital signatures best fit the combined basement ages of the Congo-Tanzania-Bangweulu block and central Madagascar (Azania), thus linking the tectonic evolution of the southernmost tip of India to these domains throughout much of the Proterozoic. The diachroneity of metamorphic ages obtained from the rims of Madurai block detrital zircons attests to their poly-metamorphic history that is different from that of the Salem block. The contrasting metamorphic and depositional histories between the Salem and Madurai blocks place them on opposite sides of the Mozambique Ocean until the latest Neoproterozoic when they came together to form Gondwana.
A region of metamorphosed supracrustal rocks (pelite, quartzite, marble, and graywacke) and coeval intrusive igneous rocks crop out in a 250 km long orogenic belt in northern Madagascar. The NW-SE trending belt is situated between a juvenile Neoproterozoic magmatic arc terrane (to the north) and an Archean craton, strongly reworked in early Neoproterozoic times (∼800-670 Ma), to the south. Pelitic schist and granulite exposed along a ∼70 km long transect from Andapa to Sambava contain assemblages ranging from sillimanite-garnet-biotite-orthoclase-cordierite to sillimanite-garnet-biotite-orthoclase and sillimanite-garnet-biotite-muscovite. These assemblages crop out over much of the area in which migmatites and hornblende + augite ± hypersthene ± biotite + perthite granites are common. Partial melting, biotite dehydration reactions, and granite emplacement are interpreted to have been nearly synchronous on the basis of field, structural, and petrographic observations. Pressure and temperature estimates from garnetiferious metapelitic granulite and pelitic migmatite are generally in the range of 6.5-8.5 kbar and 800-900°C using conventional thermobarometric methods. The occurrence of cordierite moats and discordant, but synmetamorphic, leucosomes in the granulites suggest an isothermal decompression-type path. Similarly, a core-rim P-T trajectory indicates ca. 2-3 kbar decompression at high temperature in the metapelitic granulite. U-Pb geochronology of sphene, monazite, and zircon in various metamorphic and igneous rocks from the same region yields a Cambrian age of 510-520 Ma for the time of gneiss formation, granulite metamorphism, and igneous activity. Calculated minimum cooling rates range from 6 to 18°C/Ma. Such cooling rates are more rapid than those associated with normal isostatic processes, and suggest that the terrane was tectonically exhumed at high temperature.
U–Pb baddeleyite ages and paleomagnetic poles obtained for dykes on Devon Island and Ellesmere Island in the Canadian Arctic and the Thule region of Greenland show that they are associated with the Franklin magmatic event. This study is the only one devoted to Franklin igneous rocks where a primary paleomagnetic remanence and U–Pb age have been obtained from the same rocks. Ages from this study range from 721 to 712 Ma, but paleomagnetic directional data show no clear age progression. The paleomagnetic poles from each of the two regional subsets are significantly different at the 95% confidence level from paleomagnetic results previously published for the Franklin event in the Canadian Shield. The difference in the pole locations can be accounted for, to first approximation, by a simple model of early Cenozoic block rotations among the North American plate, Greenland, and a hypothesized ancient microplate comprising Ellesmere, Devon, Cornwallis, and perhaps Somerset islands. A new grand-mean paleopole for the Franklin event, including restoration of Greenland and the proposed “Ellesmere microplate” to North America, is located at (8.4°N, 163.8°E, A 95 = 2.8°, N = 78 sites) and is a key pole for Neoproterozoic supercontinent reconstructions.
The history of the South China Craton and the constituent Yangtze and Cathaysia blocks are directly linked to Earth's Phanerozoic and Precambrian record of supercontinent assembly and dispersal. Exposed Archean rocks are limited to isolated fragments in the Yangtze Block that preserve a record of Meso- to Neo-Archean magmatism, sedimentation and metamorphism associated with a period of global craton formation and stabilization that corresponds with the assembly of the Kenor supercontinent/supercraton. However, there are insufficient data to link its history with other similar aged cratons. The tectonostratigraphic record in South China in the Paleoproterozoic, corresponding with the assembly of Nuna, suggests that rock units in the Yangtze Block were spatially linked with northwestern Laurentia and possibly Siberia, whereas Cathaysia was joined to northern India. During the formation of Rodinia at the end of the Mesoproterozoic through to that of Pangea in the mid-Paleozoic, Cathaysia remained joined to northern India. Early Neoproterozoic supra-subduction zone magmatic arc-back arc assemblages ranging in age from ~ 1000 Ma to 810 Ma occur within Cathaysia, along its northwestern margin, and along the southeastern margin of the Yangtze Block. These rocks provide a record of convergent plate interaction, which continued along the western margin of the Yangtze Block until around 700 Ma and correlates with similar along strike subduction zone magmatism in northwest India, Seychelles and Madagascar. During the final assembly of Gondwana in the early Paleozoic suturing of India-South China with the Western Australia-Mawson blocks along the Kuunga Orogen resulted in the accretion of the Sanya Block of Hainan Island with the rest of Cathaysia. The accretion of Laurussia to Gondwana in the mid-Paleozoic to form Pangea corresponds with the initiation of lithospheric extension along the northern margin of Gondwana and the separation of a number of continental blocks, including South China, which then drifted northward across the Paleo-Tethys to collide with the Asian segment of Pangea in the Permo-Triassic.
The Southern Granulite terrane, southern India, comprises a vast exposure of deep crust and forms a key region in the reconstruction of the Gondwana supercontinent. An E-W–trending crustal-scale shear zone, the Palghat-Cauvery suture zone system, which formed during the late Neoproterozoic–Cambrian (0.75–0.50 Ga), marks a
prominent terrane boundary separating terranes with a predominantly late Neoarchean (ca. 2.5 Ga) regional granulite metamorphism to the north from those with an Ediacaran–Cambrian (0.63–0.50 Ga) regional granulite
metamorphism to the south. Focusing on the younger granulite metamorphic domains, we present here new zircon U-Pb ages and Hf isotopic compositions for 11 charnockite orthogneisses from the Madurai, Trivandrum,
and Nagercoil blocks and contribute to the resolution of the age of their magmatic protoliths. This study shows that the charnockite orthogneisses south of the Palghat-Cauvery suture zone relate to a minimum of four distinct episodes of felsic magmatism centered at: ca. 2.62–2.46 Ga, ca. 2.05–1.84 Ga, ca. 1.0–0.9 Ga, and ca. 0.80–0.76 Ga, pertaining to the Siderian, Orosirian, and Tonian Periods. Hafnium isotope analyses of zircon grains from the charnockite gneisses suggest that the protoliths of the ca. 2.05–1.98 Ga gneisses from the Trivandrum and Nagercoil blocks and the ca. 1.0–0.9 Ga gneisses along the southeastern Madurai block involved a significant juvenile magma component, while the
protoliths of charnockite gneisses elsewhere
in the Madurai block formed mainly through
recycling of older crust up to ca. 3.2 Ga. A regional
granulite-facies metamorphic imprint
during the Ediacaran–Cambrian marked an
advanced stage in the amalgamation of the
Madurai, Trivandrum, and Nagercoil blocks
into the East African orogen and its collision
with the Dharwar craton.
A new statistical method is proposed to compare crustal terranes and to cluster terranes into crustal provlnces, regions and realms. Geochronological data on mafic igneous rocks, felsic igneous rocks, deformation history and Nd model age were collected from the recent literature for over 100 terranes. The 54 selected Laurentian terranes cluster into 9 provinces including a previously well recognized very distinctive SW USA province, region and realm. The 38 selected Australian terranes cluster into six provinces including a distinctive Gawler Province. A combined dendrogram of the 100 terranes from Laurentia, Australia and Antarctica results in 8 superprovinces and 11 provinces. Five of the superprovinces contain both Laurentian and Australian terranes. The inclusion of the Nevada-Califomian Mojave and the San Gabriel terranes in an otherwise Australian superprovince that includes Broken Hill and Mt Isa terranes, strongly supports the AUSWUS Laurentia-Australia reconstruction rather than the SWEAT reconstruction. Low statistical similarities between western Laurentia and eastern Antarctica fail to support the SWEAT hypothesis whilst high similarities between Canadian and north Australian terranes provides weak support for AUSWUS.
The Dahomey belt in Togo and Benin is an important segment of the larger West Gondwana Orogen. Here, we review the geodynamic evolution of the Dahomey belt and discuss new U-Pb and Lu-Hf zircon data in light of similar data previously acquired on the geologically related Northern Borborema Province, in NE Brazil. Eighteen samples from different tectonic settings and regions within the belt were collected for zircon isotopic investigation. Passive margin deposits of the Atacora Structural Unit and lower units of the Volta Basin have detrital zircon signatures compatible with the flanking West Africa Craton. The arc-related magmatism resulted from the east-dipping subduction of the Goiás-Pharusian oceanic lithosphere and is represented by a variety of granitoids emplaced in the Benino-Nigerian Shield between 670 and 610 Ma. These granitoids were mainly sourced from crustal material with subordinate juvenile input. Detrital zircon ages from syn-orogenic deposits in Benino-Nigerian Shield suggest that arc development could have started as early as 780 Ma. The main period of melting in the internal part of the belt, the Benino-Nigerian Shield, is related to crustal thickening and occurs only ca. 30 m.y. after initiation of the continental collision, marked by the ca. 610 Ma UHP (ultra-high pressure) metamorphism recorded at Lato Hills. Foreland development represented by the upper units of the Volta basin developed soon after continental collision and persisted with the development of the west-verging thrust front synchronously with the main period of crustal melting due to collision at 580 Ma. The subvertical Transbrasiliano Lineament in South America, that corresponds to the Kandi Lineament in Africa, provides a present-day fit between NW Africa and NE Brazil. Restoration of the movement of the Transbrasiliano-Kandi Lineament (strike-slip plate boundary) places the Dahomey belt and Borborema Province (NE Brazil) along the same section of the West Gondwana Orogen. This configuration would explain some of the misfits previously discussed in the literature and aligns the UHP eclogites in Togo and NE Brazil.
During Neoproterozoic Snowball Earth glaciations, the oceans gained massive amounts of alkalinity, culminating in the deposition of massive cap carbonates on deglaciation. Changes in terrestrial runoff associated with both breakup of the Rodinia supercontinent and deglaciation can explain some, but not all of the requisite changes in ocean chemistry. Submarine volcanism along shallow ridges formed during supercontinent breakup results in the formation of large volumes of glassy hyaloclastite, which readily alters to palagonite. Here we estimate fluxes of calcium, magnesium, phosphorus, silica and bicarbonate associated with these shallow-ridge processes, and argue that extensive submarine volcanism during the breakup of Rodinia made an important contribution to changes in ocean chemistry during Snowball Earth glaciations. We use Monte Carlo simulations to show that widespread hyaloclastite alteration under near-global sea-ice cover could lead to Ca2+ and Mg2+ supersaturation over the course of the glaciation that is sufficient to explain the volume of cap carbonates deposited. Furthermore, our conservative estimates of phosphorus release are sufficient to explain the observed P:Fe ratios in sedimentary iron formations from this time. This large phosphorus release may have fuelled primary productivity, which in turn would have contributed to atmospheric O2 rises that followed Snowball Earth episodes.
Evidence supports the hypothesis that the Laurentian and East Antarctic-Australian cratons were continuous in the late Precambrian and that their Pacific margins formed as a conjugate rift pair. A geometrically acceptable computer-generated reconstruction for the latest Precambrian juxtaposes and aligns the Grenville front that is truncated at the Pacific margin of Laurentia and a closely comparable tectonic boundary in East Antarctica that is truncated along the Weddell Sea margin. Geologic and paleomagnetic evidence also suggests that the Atlantic margin of Laurentia rifted from the proto-Andean margin of South America in earliest Cambrian time. -from Author
Middle-to-Late Proterozoic stratigraphy and metallogeny in the eastern part of the Canadian Cordillera and in South Australia are strikingly similar. In both areas, thick, predominantly shallow-water strata and their contained mineral deposits can be divided into three sequences (A, B, C) that record eposodic and prolonged continental rifting. It is proposed that Adelaidean strata of Australia were deposited adjacent to Belt-Purcell, Mackenzie Mountains and Windermere strata of the Canadian Cordillera within an epicontinental trough of a "Hudsonia' megacontinent. With the final rifting of this trough, the paleo-Pacific ocean was born. By Early Cambrian time, Australia-Antarctica was on the trailing "east' side of the nascent megacontinent, Gondwana, and was being modified on the "west' by accretion in the Pan-African event. North America, more or less surrounded by trailing edges at this time, was analogous to the Cenozoic African plate. This hypothesis accommodates the available paleomagnetic and radiometric data. It has implications for pre-Pangean plate tectonics, paleogeography, and the predictive metallogeny of both areas. -Authors
Gondwana amalgamated along a suite of Himalayan-scale collisional orogens, the roots of which lace the continents of Africa, South America, and Antarctica. The Southern Granulite Terrane of India is a generally well-exposed, exhumed, Gondwana-forming orogen that preserves a record of the tectonic evolution of the eastern margin of the East African Orogen during the Ediacaran-Cambrian (circa 600–500 Ma) as central Gondwana formed. The deformation associated with the closure of the Mozambique Ocean and collision of the Indian and East African/Madagascan cratonic domains is believed to have taken place along the southern margin of the Salem Block (the Palghat-Cauvery Shear System, PCSS) in the Southern Granulite Terrane. Investigation of the structural fabrics and the geochronology of the high-grade shear zones within the PCSS system shows that the Moyar-Salem-Attur shear zone to the north of the PCSS system is early Paleoproterozoic in age and associated with dextral strike-slip motion, while the Cauvery shear zone (CSZ) to the south of the PCSS system can be loosely constrained to circa 740–550 Ma and is associated with dip-slip dextral transpression and north side-up motion. To the south of the proposed suture zone (the Cauvery shear zone), the structural fabrics of the Northern Madurai Block suggest four deformational events (D1–D4), some of which are likely to be contemporaneous. The timing of high pressure-ultrahigh temperature metamorphism and deformation (D1–D3) in the Madurai Block (here interpreted as the southern extension of Azania) is constrained to circa 550–500 Ma and interpreted as representing collisional orogeny and subsequent orogenic collapse of the eastern margin of the East African Orogen. The disparity in the nature of the structural fabrics and the timing of the deformation in the Salem and the Madurai Blocks suggest that the two experienced distinct tectonothermal events prior to their amalgamation along the Cauvery shear zone during the Ediacaran/Cambrian.
The Jiangnan fold belt separates the Yangtze and Cathaysia blocks in South China and has long been considered Grenvillian in age in order to place South China in central Rodinia. It consists of deformed Early Neoproterozoic strata that are unconformably overlain by undeformed Late Neoproterozoic strata and intruded by undeformed and unmetamorphosed granitic plutons. Zircons from the Early Neoproterozoic strata yield U-Pb ages as young as 830 Ma, and one granitic pluton has a zircon U-Pb age of ca. 827 Ma. The >= 830 Ma mafic rocks along the southeastern margin of the Yangtze block have arc-affinity geochemical characters, whereas mafic rocks younger than 830 Ma have typical ocean island basalt (OIB)-like compositions. Thus, we suggest that the Early Neoproterozoic strata were deposited on an active continental margin prior to amalgamation of the Yangtze and Cathaysia blocks at ca. 830 Ma. The overlying Late Neoproterozoic strata were deposited in the intracontinental rifted Nanhua Basin at 820-730 Ma and probably reflect backarc spreading above the long-lived (950-735 Ma) oceanic subduction zone along the northern and western margin of the Yangtze block. This model is consistent with the secular tectonic evolution of South China during the Neoproterozoic. The Jiangnan fold belt is therefore not a Grenvillian feature as previously suggested, and there is no evidence to place South China in central Rodinia. Instead, we believe that South China was located in a marginal position relative to this supercontinent.
New palaeogeographical reconstructions are presented at 10 myr intervals from the Lower Cambrian at 540 Ma to the Lower Devonian at 400 Ma, showing continental crustal fragments and oceans (not lands and seas), with appropriate kinematic continuity between successive maps. The maps were chiefly generated by revised and selected palaeomagnetic data and revised Apparent Polar Wandering paths linked to present-day polygons from the main continents. These have been reinforced by analysis of the distributions of some fossils and sediments. Gondwana was the dominating supercontinent from its final assembly in the Latest Neoproterozoic at about 550 Ma until the Carboniferous, and covered much of the Southern Hemisphere. The Northern Hemisphere was largely occupied by the vast Panthalassic Ocean. The relative positions of the major continents and the latitudes and rotation histories of Gondwana, Baltica, Siberia and Laurentia (Laurussia from the mid-Silurian) are now well known. Although Laurentia was oriented in a similar direction to the present, Siberia was inverted throughout the Lower Palaeozoic, and Baltica too was initially inverted, but rotated through 120 degrees between the Late Cambrian and Late Ordovician before collision with Laurentia in the mid-Silurian Caledonide Orogeny. Through reconstructions of the Caledonide and some other orogenies, the progressive history of the Iapetus Ocean between Laurentia and Baltica/Gondwana is well constrained. Less major continents whose positions are also well known include Avalonia (initially peri-Gondwanan but migrating in the Early Ordovician to join Baltica by the end of the Ordovician), Sibumasu (now considered an integral part of Gondwana) and Mongolia (adjacent to Siberia). A large number of other terranes are reviewed and plotted on the reconstructions with varying degrees of certainty. However, significant continents with less well constrained or controversial positions are South China, North China (Sinokorea), Annamia (Indochina) and Arctic Alaska-Chukotka. The European areas of France, Iberia and southern Italy, previously considered by some as a separate Armorican Terrane Assemblage, remained parts of core Gondwana until the opening of the Palaeotethys Ocean near the end of the Silurian, but it is uncertain whether Perunica (Bohemia) was one of that group or whether it left Gondwana during the Middle Ordovician.
The supercontinent Rodinia is hypothesized to have been assembled and positioned in tropical latitudes by the early Neoproterozoic Era. Paleomagnetic data from limestones of Svalbard and basaltic dikes of South China have been interpreted to record rapid changes in paleogeography driven by true polar wander that may have rotated the supercontinent in association with the similar to 800 Ma Bitter Springs carbon isotope event. To further constrain early Neoproterozoic paleogeography and to test proposed rapid rotations, we have developed sequence- and chemo-stratigraphically constrained paleomagnetic data from the Bitter Springs Formation of the Amadeus Basin of central Australia. A new paleomagnetic pole for the post-Bitter Springs stage similar to 770 Ma Johnny's Creek Member (Bitter Springs Formation) provides a positive test for a long-lived history of Australia and Laurentia in a single supercontinent as its similar position to late Mesoproterozoic north Australia poles reproduces the closure of the Laurentian "Grenville Loop." This new pole also provides support for the hypothesis that there was significant rotation between north and south+west Australia at the end of the Neoproterozoic as this rotation brings the south+west Australia similar to 755 Ma Mundine Well pole into much closer proximity to the north Australia Johnny's Creek pole. Syn-Bitter Springs stage carbonates of the Love's Creek Member of the formation contain a well-behaved remanence held by magnetite. The direction of this remanent magnetization falls on the Cambrian portion of Australia's apparent polar wander path suggesting that the magnetite may have formed authigenically at that time. If primary, the Love's Creek direction is consistent with the true polar wander hypothesis for the Bitter Springs stage, is internally consistent with the relative sea level changes inferred from the formation, and can constrain Australia to a SouthWest North America East AnTarctica (SWEAT) fit. A remanence held by pyrrhotite in carbonates of the Bitter Springs Formation corresponds to the apparent polar wander path of Australia at similar to 350 Ma. This component can be used to constrain the history of the Devonian-Carboniferous Alice Springs Orogeny as it demonstrates that regional folding of basinal sediments occurred prior to similar to 350 Ma, but that the latest stages of tectonism in the hinterland drove fluids through the sediments that altered redox conditions to favor pyrrhotite precipitation.
U–Pb age data from southwest Madagascar provide a compelling case that the pre-Gondwana Indian plate was stitched with the arc terranes of the Arabian Nubian Shield along a suture that closed between 580 Ma and 520 Ma. The key observations supportive of this interpretation are: (1) metamorphism dated to 630–600 Ma is manifested only on the west side of the suture in rocks that have affinities with the oceanic and island arc terranes of the Arabian Nubian Shield, or which represent continental rocks welded to these terranes prior to the amalgamation of Gondwana, and (2) orogenesis at 580–520 Ma is manifest in rocks on both sides of the suture, an observation taken to mark the timing of collision and to reflect spatial continuity across the suture. In southwest Madagascar the distribution of metamorphic ages places the suture along the Beraketa high-strain zone, the tectonic boundary between the Androyen and Anosyen domains. Similar age relationships allow for the extrapolation of this tectonic boundary into both East Antarctica and Africa.
A set of global paleogeographic reconstructions for the 1770–1270 Ma time interval is presented here through a compilation of reliable paleomagnetic data (at the 2009 Nordic Paleomagnetic Workshop in Luleå, Sweden) and geological constraints. Although currently available paleomagnetic results do not rule out the possibility of the formation of a supercontinent as early as ca. 1750 Ma, our synthesis suggests that the supercontinent Nuna/Columbia was assembled by at least ca. 1650–1580 Ma through joining at least two stable continental landmasses formed by ca. 1.7 Ga: West Nuna (Laurentia, Baltica and possibly India) and East Nuna (North, West and South Australia, Mawson craton of Antarctica and North China). It is possible, but not convincingly proven, that Siberia and Congo/São Francisco were combined as a third rigid continental entity and collided with Nuna at ca.1500 Ma. Nuna is suggested to have broken up at ca. 1450–1380 Ma. West Nuna, Siberia and possibly Congo/São Francisco were rigidly connected until after 1270 Ma. East Nuna was deformed during the breakup, and North China separated from it. There is currently no strong evidence indicating that Amazonia, West Africa and Kalahari were parts of Nuna.
Neoproterozoic igneous rocks are widespread along the western margin of the Yangtze Block, but their petrogenesis and tectonic setting is debated. The Guandaoshan pluton is located at the southwestern margin of the Yangtze Block and is mainly composed of diorite and subordinate gabbro, with quartz diorite in its margin. Hornblende is a ubiquitous mineral in different phases of the pluton. SHRIMP zircon U-Pb dating of quartz diorite, gabbroic diorite, and gabbro from the pluton yielded 206Pb/238U ages of 857 ± 7 Ma, 856 ± 6 Ma, and 856 ± 8 Ma, respectively. Guandaoshan pluton samples show a large range of SiO2 (47.02 − 67.66%), MgO (1.12 − 7.5%), Fe2O3T (2.8 − 12.22%) and CaO (2.95 − 11.88%), low rare earth element (REE) contents from 22 to 49 ppm, and enrichment of Sr, Ba and Rb and depletion of Nb, Zr and Ti with characteristics of island arc magma. They also exhibit low initial 87Sr/86Sr ratios from 0.7030 − 0.7033, and positive εNd(t) values from + 4.8 to + 5.2. These features suggest that the parental magma of the Guandaoshan pluton originated at a convergent plate boundary from a depleted mantle source modified by slab fluids, and underwent the fractional crystallization of amphibole and magnetite, without significant crustal assimilation, during the formation from gabbro-diorite to quartz diorite. Neoproterozoic magmas with age of 860 − 740 Ma are abundant on the western Yangtze Block, and there is a gap of magmatism in early Neoproterozoic (from about 1000 Ma to 870 Ma). Therefore, it can be duduced that the ~ 860 Ma Guandaoshan pluton and the contemporary magmatism represent initial subduction at the western margin of the Yangtze Block. Based on the Neoproterozoic paleomagnetic data, detrital zircon ages, magmas with low δ18O values in South China and our new data, we prefer that the South China Block was located at the margin of Rodinia in the Neoproterozoic, and not the center of the supercontinent.
Determining the effects of compaction-related inclination shallowing of
remanence directions is crucial for ascertaining the validity of low
palaeolatitudes for Neoproterozoic red beds in South Australia that are
central to the debate concerning low-latitude Proterozoic glaciation.
The inclination correction (or flattening) factor, f, is defined as
tan(ID)/tan(IF), where ID and
IF are the inclinations of the measured detrital remanence
and the ancient inducing field, respectively. The anisotropy can be
estimated using anisotropy of magnetic susceptibility and the anisotropy
of high-field isothermal remanence (hf-AIR). The
elongation-inclination (E-I) method has also been used to
infer inclination shallowing. We add the anisotropy of thermoremanent
magnetisation (ATR) to these methods. For the late Cryogenian Elatina
Formation arenites, which constitute the bulk of the Elatina data set,
the inclination correction using f = 0.738 derived from ATR increases
the palaeolatitude of the Elatina Formation from 6.5 ± 2.2°
to 8.8 ± 3.2°, which confirms that the Elatina glaciation
occurred near the palaeoequator. Inclination corrections for the
Ediacaran argillaceous Brachina and Wonoka formations, using f =
0.35-0.38 derived from ATR, are significantly greater than for the
more arenaceous Elatina Formation, which increases their palaeolatitudes
from ~ 12° to ~ 30°. Carbonates from the basal Ediacaran
Nuccaleena Formation yielded f = 0.8 from ATR, which represents only a
small palaeolatitude correction from 19° to 23°. The anisotropy
results imply that the characteristic remanent magnetisations carried by
all these units were acquired early as depositional remanent
magnetisations, essentially at the time of deposition. The shift of the
palaeopoles from argillaceous units indicating significantly higher
palaeolatitudes introduces a distinctive loop into the late
Cryogenian-Ediacaran-Cambrian pole path for Australia. This
loop shows similarities with the North American pole path for this
period, for which true polar wander (TPW) has been inferred. However,
until ages of Neoproterozoic strata in South Australia are better
constrained uncertainty persists on whether the similarities of the
Australian and North American pole paths reflect TPW.
Reconstructions of Gondwana place Dronning Maud Land, Antarctica (DML) adjacent to N. Mozambique prior to fragmentation. The Monapo Complex outlier klippen overlying the Nampula Terrane in N. Mozambique has been correlated with rocks in eastern and central DML. Metamorphic assemblages and P–T conditions from the two areas are compared as well the timing of metamorphism. Granulite grade assemblages preserved in the Monapo Complex suggest P–T conditions of ∼900 °C and >10 kb. Textures vary with reactions typical of isothermal decompression, isobaric cooling and hydration being recognized but also include equilibrium assemblages. P–T estimates from four samples suggest initial inversion of high pressure assemblages from at least ∼10 kb and ∼900 °C to mid-crustal levels where near isobaric cooling and hydration at between ∼4–7 kb and 550–700 °C is recognized. Granulite grade assemblages from Balchenfjella in eastern Sør Rondane, DML suggest initial P–T conditions of ∼900 °C and >10 kb. Textures vary with reactions typical of decompression, cooling and hydration being recognized but also include equilibrium assemblages. P–T estimates from four samples suggest initial inversion of high pressure assemblages from at least ∼10 kb and ∼900 °C to mid-crustal levels where retrogression at between ∼6–7 kb and 600–700 °C is recognized.
As the chronicle of plate motions through time, paleogeography is fundamental to our understanding of plate tectonics and its role in shaping the geology of the present-day. To properly appreciate the history of tectonics—and its influence on the deep Earth and climate—it is imperative to seek an accurate and global model of paleogeography. However, owing to the incessant loss of oceanic lithosphere through subduction, the paleogeographic reconstruction of ‘full-plates’ (including oceanic lithosphere) becomes increasingly challenging with age. Prior to 150 Ma ∼60% of the lithosphere is missing and reconstructions are developed without explicit regard for oceanic lithosphere or plate tectonic principles; in effect, reflecting the earlier mobilistic paradigm of continental drift. Although these ‘continental’ reconstructions have been immensely useful, the next-generation of mantle models requires global plate kinematic descriptions with full-plate reconstructions. Moreover, in disregarding (or only loosely applying) plate tectonic rules, continental reconstructions fail to take advantage of a wealth of additional information in the form of practical constraints. Following a series of new developments, both in geodynamic theory and analytical tools, it is now feasible to construct full-plate models that lend themselves to testing by the wider Earth-science community. Such a model is presented here for the late Paleozoic (410-250 Ma) together with a review of the underlying data. Although we expect this model to be particularly useful for numerical mantle modeling, we hope that it will also serve as a general framework for understanding late Paleozoic tectonics, one on which future improvements can be built and further tested.
Precambrian data from Australia include the oldest palaeopole yet defined, the record of one of the oldest geomagnetic polarity reversals, the most definitive evidence for low-latitude Neoproterozoic glaciation, the first study of BIFs and the timing/nature of iron-ore genesis, the most unusual ‘field test’ (impact melt rock and ejecta horizon host rocks), some of the best examples of complete contact tests and the timing of craton assembly. Some old caveats that can no longer be ignored, such as corrections for inclination flattening and the permitting of rotations between contiguous intracontinental cratons to bring conflicting palaeopoles into alignment are required. Care should be exercised when inferring palaeolatitudes from sedimentary derived palaeoinclinations. TPW should only be considered if there is evidence from more than one, and preferably more, independent continents. Future work identified includes a complete magnetostratigraphic study of ~ 300 my Adelaidean succession, better age constraints for the Adelaidean and Officer Basin successions and a better age for the Gawler Craton GB dykes.