Figure 2 - uploaded by Richard Mark Palin
Content may be subject to copyright.
Schematic cross section through the present-day Earth outlining differences in composition (left) and rheology (right) between layers. Not to scale.
Source publication
The Earth as a planetary system has experienced significant change since its formation c. 4.54 Gyr ago. Some of these changes have been gradual, such as secular cooling of the mantle, and some have been abrupt, such as the rapid increase in free oxygen in the atmosphere at the Archean-Proterozoic transition. Many of these changes have directly affe...
Contexts in source publication
Context 1
... in their mantles can exhibit a variety of geodynamic regimes at their surfaces, which may readily transition between different states over the thermal lifetime of the parent body ( Petersen et al., 2015). All discussion of 'plates' in this work and related literature refers specifically to discrete masses of a planet's lithosphere (Barrell, 1914: Fig. 2), which defines the uppermost solid layer of the Earth, and is distinguished from the underlying asthenosphere by changes in the dominant mode of heat flow, chemical composition, and/or rheology at the interface (Anderson, 1995;Fischer et al., 2010;Green et al., 2010). From a thermal perspective, heat flow through the lithosphere is ...
Context 2
... and Jordan, 2003). The lithosphere may alternatively be referred to as a "lid" as it represents a strong thermal boundary layer separating hot planetary interiors from the cold hydrosphere and surrounding vacuum of space. Finally, it should be emphasized that discussion in this study refers only to rocky planets with silicate crusts and mantles ( Fig. 2), although lithosphere-asthenosphere nomenclature may be equally applied to ice-rich bodies with solid outer shells situated above subsurface liquid oceans (e.g. Roberts and Nimmo, 2008). Two fundamental end-member geodynamic regimes may exist on large silicate bodies, such as the Earth: mobile and stagnant lids. Mobile lids are ...
Context 3
... voluminous subducted materials during ocean closure associated with supercontinent assembly temporarily accumulate in the mantle transition zone at 410-660 km depth (Fig. 2), from where they sink to the core-mantle boundary and accumulate as 'slab graveyards' (Fig. 2: Maruyama et al., 2007). Melting of the slab graveyards through heating from the core provides a potential trigger for the formation of superplumes, which ascend from the core-mantle boundary, eventually diverging into hot spots (Condie, 2001) ...
Context 4
... voluminous subducted materials during ocean closure associated with supercontinent assembly temporarily accumulate in the mantle transition zone at 410-660 km depth (Fig. 2), from where they sink to the core-mantle boundary and accumulate as 'slab graveyards' (Fig. 2: Maruyama et al., 2007). Melting of the slab graveyards through heating from the core provides a potential trigger for the formation of superplumes, which ascend from the core-mantle boundary, eventually diverging into hot spots (Condie, 2001) and rifting the supercontinent. Plumes rising from the core-mantle boundary facilitate heat and mass transport ...
Context 5
... is a high-pressure polymorph of carbon that stabilizes at minimum pressures of ~3.5-4.5 GPa at ~600-1200 °C, equivalent to at least 150-180 km depth within the Earth's upper mantle (Khaliullin et al., 2011; Day, 2012: Figs. 2 and 7). A rarer variety of "superdeep" diamonds are thought to have originated from > 410 km depth, within the mantle transition zone (e.g. Timmerman et al., 2019). As such, during growth, diamonds can trap minerals, fluids, or melts that are stable at various depths within the Earth's interior. Based on their morphology and internal growth ...
Context 6
... in their mantles can exhibit a variety of geodynamic regimes at their surfaces, which may readily transition between different states over the thermal lifetime of the parent body ( Petersen et al., 2015). All discussion of 'plates' in this work and related literature refers specifically to discrete masses of a planet's lithosphere (Barrell, 1914: Fig. 2), which defines the uppermost solid layer of the Earth, and is distinguished from the underlying asthenosphere by changes in the dominant mode of heat flow, chemical composition, and/or rheology at the interface (Anderson, 1995;Fischer et al., 2010;Green et al., 2010). From a thermal perspective, heat flow through the lithosphere is ...
Context 7
... and Jordan, 2003). The lithosphere may alternatively be referred to as a "lid" as it represents a strong thermal boundary layer separating hot planetary interiors from the cold hydrosphere and surrounding vacuum of space. Finally, it should be emphasized that discussion in this study refers only to rocky planets with silicate crusts and mantles ( Fig. 2), although lithosphere-asthenosphere nomenclature may be equally applied to ice-rich bodies with solid outer shells situated above subsurface liquid oceans (e.g. Roberts and Nimmo, 2008). Two fundamental end-member geodynamic regimes may exist on large silicate bodies, such as the Earth: mobile and stagnant lids. Mobile lids are ...
Context 8
... voluminous subducted materials during ocean closure associated with supercontinent assembly temporarily accumulate in the mantle transition zone at 410-660 km depth (Fig. 2), from where they sink to the core-mantle boundary and accumulate as 'slab graveyards' (Fig. 2: Maruyama et al., 2007). Melting of the slab graveyards through heating from the core provides a potential trigger for the formation of superplumes, which ascend from the core-mantle boundary, eventually diverging into hot spots (Condie, 2001) ...
Context 9
... voluminous subducted materials during ocean closure associated with supercontinent assembly temporarily accumulate in the mantle transition zone at 410-660 km depth (Fig. 2), from where they sink to the core-mantle boundary and accumulate as 'slab graveyards' (Fig. 2: Maruyama et al., 2007). Melting of the slab graveyards through heating from the core provides a potential trigger for the formation of superplumes, which ascend from the core-mantle boundary, eventually diverging into hot spots (Condie, 2001) and rifting the supercontinent. Plumes rising from the core-mantle boundary facilitate heat and mass transport ...
Context 10
... is a high-pressure polymorph of carbon that stabilizes at minimum pressures of ~3.5-4.5 GPa at ~600-1200 °C, equivalent to at least 150-180 km depth within the Earth's upper mantle (Khaliullin et al., 2011; Day, 2012: Figs. 2 and 7). A rarer variety of "superdeep" diamonds are thought to have originated from > 410 km depth, within the mantle transition zone (e.g. Timmerman et al., 2019). As such, during growth, diamonds can trap minerals, fluids, or melts that are stable at various depths within the Earth's interior. Based on their morphology and internal growth ...
Similar publications
Although there is evidence for periodic geological perturbations driven by regular or semi-regular extra-terrestrial bombardment, the production of Earth’s continental crust is generally regarded as a function of planetary differentiation driven by internal processes. We report time series analysis of the Hf isotopic composition of zircon grains fr...
The generation of continental crust, its bulk composition and temporal evolution provide important records of plate tectonics and associated magma generating processes. However, the long-term integrated effects of repeated magmatic events on crustal growth, composition and differentiation and therefore, on crustal evolution are rarely considered. H...
Ultramylonites—intensely deformed rocks with fine grain sizes and well‐mixed mineral phases—are thought to be a key component of Earth‐like plate tectonics, because coupled phase mixing and grain boundary pinning enable rocks to deform by grain‐size‐sensitive, self‐softening creep mechanisms over long geologic timescales. In isoviscous two‐phase co...
The authors of the idea of linking strip magnetic anomalies with the formation of their sources under the influence of the Earth’s alternating magnetic field thought it possible to study the movement of lithospheric plates with their help. Most of them quickly abandoned such intentions. Nevertheless, most geophysicists in the world believe this is...
The short‐lived radionuclide system ¹⁴⁶Sm‐¹⁴²Nd can provide direct information about geological differentiation events in the terrestrial Hadean (>4.0 Ga) mantle. The spatiotemporal formation and evolution of crustal material that formed from different mantle domains can constrain the existing geodynamic environment in which continental crust forme...
Citations
... The models consider the deformation of a viscoplastic medium under the action of applied tectonic forces. [65], modified). Geotherms for surface of plates under modern conditions (according to [69]) for subduction zones: cold (blue line), warm (red line); water solidi of basalt (according to [82]) (green dashed line) and peridotite (according to [47]) (blue dashed line). ...
In this article we examine the effects of eclogitization of slab rocks on the subduction regime under
a continent. Eclogitization of rocks in high-pressure metamorphic complexes occurs only in the areas of penetration
of hydrous fluid. In the absence of hydrous fluid, the kinetic delay of eclogitization preserves lowdensity
rocks under P‒T conditions of eclogite metamorphism, delaying the weighting of a slab and reducing
the efficiency of the slab-pull mechanism, which contributes to steep subduction into the deep mantle. The
results of numerical petrological–thermomechanical 2D modeling of subduction under a continent in a wide
range of eclogitization parameters of oceanic crustal rocks (discrete eclogitization) are presented. The effects
of a lower kinetic delay of eclogitization in a water-bearing basalt layer, compared to a drier underlying gabbro
layer, have been tested. Based on the results of 112 numerical experiments with 7 variants of eclogitization
ranges (400–650°C for basalt and 400–1000°C for gabbro) at different potential mantle temperatures (ΔT =
0–250°C, above the modern value), and steep, flat, and transitional subduction regimes were identified. The
steep subduction regime occurs under modern conditions (ΔT = 0°C) with all ranges of eclogitization. Here,
it is characterized by an increase in the angle of subduction of the slab as the plate descends, and above the
boundary of the mantle transition zone there is a flattening and/or tucking of the slab. Subduction is accompanied
by the formation of felsic and mafic volcanics and their plutonic analogues. At elevated mantle temperatures
(ΔT ≥ 150°С) and discrete eclogitization over a wide range, the flat subduction regime is observed
with periodic detachments of its steeper frontal eclogitized part. The flat subduction regime is accompanied
by significant serpentinization of the mantle wedge and sporadic, scarce magmatism (from mafic to felsic),
which occurs at a significant distance (≥500 km) from the trench. During the transition regime, which is also
achieved in models with elevated mantle temperatures, a characteristic change occurs from flat to steep subduction,
resulting in a stepped shape of the slab. As the kinetic shift of eclogitization increases, flat subduction
develops. An increase in the thickness of the continental lithosphere from 80 to 150 km contributes to steep
subduction, while the influence of the convergence rate (5–10 cm/year) is ambiguous. Discrete eclogitization
of thickened oceanic crust and depletion of lithospheric mantle in the oceanic plate are the main drivers of
flat subduction. In modern conditions, their influence becomes insignificant due to the decrease in thickness
of oceanic crust and degree of depletion of the oceanic mantle lithosphere. As a result, less frequent flat
movement of slabs is determined by other factors.
... The models consider the deformation of a viscoplastic medium under the action of applied tectonic forces. [65], modified). Geotherms for surface of plates under modern conditions (according to [69]) for subduction zones: cold (blue line), warm (red line); water solidi of basalt (according to [82]) (green dashed line) and peridotite (according to [47]) (blue dashed line). ...
In this article we examine the effects of impact of slab rocks eclogitization on the subduction regime under the continent. Eclogitization of rocks in high-pressure metamorphic complexes occurs only in the areas of penetration of hydrous fluid. In the absence of hydrous fluid, the kinetic delay of eclogitization preserves low-density rocks under P‒T conditions of eclogite metamorphism, delaying the weighting of a slab and reducing the efficiency of the slab-pull mechanism which contributes to the steep subduction into the deep mantle. The results of numerical petrological-thermomechanical 2D modeling of subduction under the continent in a wide range of eclogitization parameters of oceanic crust rocks (discrete eclogitization) are presented. The effects of a lower kinetic delay of eclogitization in the water-bearing basalt layer, compared to the drier underlying gabbro layer, have been tested. Based on results of 112 numerical experiments with 7 variants of eclogitization ranges (in range 400–650°C for basalt and 400–1000°C for gabbro) at different potential mantle temperatures (ΔT = 0–250°C, above modern value), and steep, flat and transitional subduction regimes were identified. The mode of steep subduction occurs under modern conditions (ΔT = 0°C) with all ranges of eclogitization. Here it is characterised by an increase in the angle of subduction of the slab as the plate descends, and above the boundary of the mantle transition zone there is a flattening or and then tucking of the slab. Subduction is accompanied by the formation of felsic and mafic volcanics and their plutonic analogues. At elevated temperatures of the mantle (ΔT≥150°С) and discrete eclogitization over a wide range, the flat subduction regime is observed with periodic detachments of its steeper frontal eclogitized part. The flat subduction regime is accompanied by significant serpentinization of the mantle wedge and episodic, scarce magmatism (from mafic to felsic), which occurs at a significant distance (≥500 km) from the trench. During the transition regime, which is also realised in models with elevated mantle temperatures, there is a characteristic change occurs from flat to steep subduction, resulting in a stepped shape of the slab. As the kinetic shift of eclogitisation increases, flat subduction develops. An increase in the thickness of the continental lithosphere from 80 km to 150 km contributes to the implementation of steep subduction, while the influence of the convergence rate (5–10 cm/year) is ambiguous. Discrete eclogitization of thickened oceanic crust and depletion of lithospheric mantle in the oceanic plate are the main drivers of flat subduction. In modern conditions, their influence becomes insignificant due to the decrease in the thickness of the oceanic crust and the degree of depletion of the oceanic mantle lithosphere. As a result, the less frequent flat movement of slabs is determined by other factors.
... The earliest period of enhanced layered intrusion emplacement occurs from 3.0 to 2.7 Ga, and primarily corresponds to the West Pilbara (Australia; e.g., Munni Munni, Andover, Radio Hill) and Murchison Domain (Australia; e.g., Windimurra, Narndee) intrusions, as well as other notable intrusions such as Stella (South Africa), Monts de Cristal (Gabon), and Fiskenaesset (Greenland). This interval is significant in Earth history as it follows the broadly accepted interval of global-scale subduction initiation (Palin et al. 2020), precedes the assembly of the Superia-Sclavia (or Kenorland) supercontinents (Nance et al. 2014), and correlates with a ramp-up in large igneous province magmatism (Ernst et al. 2021) as well as crustal production and differentiation (Hawkesworth et al. 2010;Dhuime et al. 2015). This newly evolving crust would have interacted with upwelling komatiitic melts generated during relatively voluminous melting (>25 %) in a hotter Archean mantle, leading to the production of siliceous high-Mg basalts that are believed to be parental to many Archean layered intrusions (West Pilbara intrusions, Hoatson and Sun 2002;Stillwater Complex, Jenkins et al. 2021). ...
... E. Global geodynamics with the continental freeboard (Bada and Korenaga 2018) and ages of local subduction initiation according to Ba contents of TTG suites (Huang et al. 2022). Plots are underlain by supercontinent ages (Bradley 2008;Nance et al. 2014), global subduction initiation (Palin et al. 2020), and the Great Oxygenation Event (GOE). reworking rates also relatively increase at ~ 1.8 Ga (Dhuime et al. 2012). ...
Layered intrusions are plutonic bodies of cumulates that form by the crystallization of mantle-derived melts. These intrusions are characterized by igneous layering distinguishable by shifts in mineralogy, texture, or composition. Layered intrusions have been fundamental to our understanding of igneous petrology; however, it is their status as important repositories of critical metals-such as platinum-group elements, chromium, and va-nadium-that has predominantly driven associated research in recent decades. Many layered intrusions were emplaced during the Precambrian, predominantly at the margins of ancient cratons during intervals of super-continent accretion and destruction. It appears that large, layered intrusions require rigid crust to ensure their preservation, and their geometry and layering is primarily controlled by the nature of melt emplacement. Layered intrusions are best investigated by integrating observations from various length-scales. At the macroscale, intrusion geometries can be discerned, and their presence understood in the context of the regional geology. At the mesoscale, the layering of an intrusion may be characterized, intrusion-host rock contact relationships studied, and the nature of stratiform mineral occurrences described. At the microscale, the mineralogy and texture of cumulate rocks and any mineralization are elucidated, particularly when novel microtextural and mineral chemical datasets are integrated. For example, here we demonstrate how mesoscale observations and microscale datasets can be combined to understand the petrogenesis of the perplexing snowball oiks outcrop located in the Upper Banded Series of the Stillwater Complex. Our data suggest that the ortho-pyroxene oikocrysts did not form in their present location, but rather formed in a dynamic magma chamber where crystals were transported either by convective currents or within crystal-rich slurries. Critical metals may be transported to the level of a nascent intrusion as dissolved components in the melt. Alternatively, ore minerals are entrained from elsewhere in a plumbing system, potentially facilitated by volatile-rich phases. There are many ore-forming processes propounded by researchers to occur at the level of emplacement; however, each must address the arrival of the ore mineral, its concentration of metals, and its accumulation into orebodies. In this contribution, several of these processes are described as well as our perspectives on the future of layered intrusion research.
... With an average annual temperature on the Earth's surface of ~7 °C, on neighboring planets Venus and Mars it was ~460 °C and -65 °C, respectively, and they did not have liquid water, which occupies ~70% of the surface on Earth [Sorokhtin, 2010]. The geochronology of the biosphere is replete with global events characterized by blurred dating and ambiguity of models of participation of cosmic and terrestrial factors in them [Dobretsov, 2008;Scotese, 2021;Palin, 2020;Planavsky, 2021]. The entire complex of these factors ensured the regulation and maintenance of the TG of the Earth's hydrosphere over long periods of geochronology in the range of ~0-42 °C, in which the thermodynamics of hydrogen bonds of water (HBs) maintains the viability of water-protein systems. ...
The increasing frequency of climate catastrophes worldwide against background of global warming and reduction of biodiversity in human ecosystem are typical signs of global extinction, the sixth in ~600 million years of Phanerozoic. The regularity of global extinctions of marine biota with a period of ~62 Myr in Phanerozoic correlates with cyclicity of tidal effects of stellar environment of Solar System as it revolves around center of Galaxy. In accordance with Anthropic Principle, abiogenic factors of mass extinctions can correct evolution along vector of anthropogenesis. Human parasitism on biosphere, demographic problems and stagnation of sapientation during 6th extinction suggest launch of mutagenesis, necessary for fixing dominance of thinking over the instinct of reproduction at level of the human genome. Taking into account chirality of bilaterals, sexual dimorphism and molecular mechanism of circadian clock, it was suggested that role of mutagenic factor is played by chiral photon-neutrino quanta, genetically linked to the neutrino of the proton-proton cycle of Sun's energy. Sensitization of biosphere to action of chiral factor at night will be provided by anomalous physicochemical properties of liquid water in hydrosphere and in physiological fluids. It is shown that the ~11-year cycle of Solar activity reflects the influence on the physics of Sun of periodicity of the tidal effects of syzygy of Jupiter, Venus and Earth, as well as interactions of magnetic dipoles of Sun and Jupiter. Synchronous with Solar activity changes in flux of chiral quanta on the night side of earth will be additionally modulated by geography and this will manifest itself in differences in mentality of population of southern and northern hemispheres of Earth, as well as coastal and continental territories.
... Геохронология биосферы изобилует глобальными событиями, характеризуемые размытой датировкой и неоднозначностью моделей участия в них космических и земных факторов [Dobretsov, 2008;Scotese, 2021;Palin, 2020;Planavsky, 2021]. Весь комплекс этих факторов обеспечивал регулировку и удержание ТG гидросферы Земли в течение длительных периодов геохронологии в интервале ~0-42 °C, в котором термодинамика водородных связей воды (HBs) сохраняет жизнеспособность водно-белковых систем. ...
Учащение климатических катастроф во всем мире и сокращение биоразнообразия в экосистеме человека являются типичными признаками глобального вымирания, шестого по счету за ~600 млн лет фанерозоя. Регулярность глобальных вымираний морской биоты с периодом ~62 Myr в фанерозое коррелирует с цикличностью приливных эффектов звездного окружения Солнечной системы в Галактике. Паразитизм человечества на биосфере и демографические проблемы в период 6-го вымирания предполагают запуск мутагенеза, необходимого для закрепления на уровне генома homo sapiens доминанты мышления над инстинктом размножения. Равнозначное участие фотонов и нейтрино в энергетике Солнца указывает на то, что в эволюции и экологии роль нейтрино не должна уступать солнечному свету. Учитывая глобальность явления гомохиральности, предложили на роль глобального хирального фактора нейтринные кванты энергии, на которые может распадаться солнечное нейтрино. Постулировав их участие в хиральной биофизике, а также в теплофизике океана и литосферы, непротиворечиво согласовали геохронологии физики Солнца и климата. Показали, что 11-летний цикл Солнечной активности комбинирует суммарное влияние на физику Солнца приливных сил планет и магнитного поля Юпитера, возмущение которого падением кометы Шумейкеров-Леви в 1994 году сразу отразилось изменениями в физике Солнца и метрологии гидросферы. Выяснили, что в эмбриогенезе жидкость бластоцисты и этап гаструляции более всего уязвимы для мутагенного действия хирального фактора, нарушающего нормальное соотношение X/Y хромосом и лево-правую висцеральную асимметрию.
The increasing frequency of climate catastrophes worldwide and reduction of biodiversity in human ecosystem are typical signs of a global extinction, the sixth in ~600 million years of Phanerozoic. The regularity of global extinctions of marine biota with a period of ~62 Myr in Phanerozoic correlates with cyclicity of tidal effects of the stellar environment of Solar System in Galaxy. Human parasitism on biosphere and demographic problems during the 6th extinction suggest the launch of mutagenesis necessary for fixing the dominance of thinking over reproductive instinct at level of homo sapiens genome. The equal participation of photons and neutrinos in energy of Sun indicates that role of neutrinos in evolution and ecology should not be inferior to sunlight. Taking into account the global nature of homochirality phenomenon, neutrino energy quanta, into which a solar neutrino can decay, were proposed as the global chiral factor. Having postulated their participation in chiral biophysics, as well as in thermal physics of ocean and lithosphere, they consistently reconciled geochronologies of solar and climate physics. They showed that the 11-year cycle of solar activity is combined effect of tidal forces of planets and magnetic field of Jupiter on physics of Sun, the disturbance of which by fall of Shoemaker-Levy comet in 1994 was immediately reflected in changes in physics of Sun and metrology of hydrosphere. They found that in embryogenesis, the blastocyst fluid and gastrulation stage are most vulnerable to the mutagenic action of chiral factor, which disrupts the normal ratio of X/Y chromosomes and left-right visceral asymmetry.
... Exemplifying the difficulty in constraining when plate tectonics began, plate tectonics onset times spanning a huge portion of Earth's history, from >4.0 Ga to ∼1 Ga, have been suggested in previous studies based on interpretations of the ancient geologic record (Korenaga, 2013;Palin et al., 2020). Hopkins et al. (2008) argued for the initiation of plate tectonics in the Hadean based on studies of the Jack Hills zircons. ...
Despite significant study, when and how plate tectonics initiated on Earth remains contentious. Geologic evidence from some of Earth's earliest cratons has been interpreted as reflecting the formation of initial continental blocks by non‐subduction processes, which then trigger subduction initiation at their margins. Numerical models of mantle convection with a plastic yield stress rheology have shown this scenario is plausible. However, whether continents can trigger subduction initiation has not been tested with other rheologies. We, therefore, use numerical models of mantle convection with an imposed continental block to test whether continents facilitate subduction initiation with a grain‐damage mechanism, where weak shear zones form by grain size reduction. Our results show that continents modestly enhance stresses in the lithosphere, but not enough to significantly impact lithospheric damage or subduction initiation: continents have minimal influence on lithospheric damage or plate speed, nor does subduction preferentially initiate at the continental margin. A new regime diagram that includes continental blocks shows only a small shift in the boundary between the mobile‐lid and stagnant‐lid regimes when continents are added. However, as we do find that stresses are modestly enhanced at the continental margin in our models, we develop a scaling law for this stress enhancement to more fully test whether continents could trigger subduction initiation on early Earth. We find that lithospheric stresses supplied by continents are not sufficient to initiate subduction on the early Earth on their own with grain‐damage rheology; instead, additional factors would be required.
... Howev er, the Bangweulu Craton is Paleoproterozoic in age, and thus younger than the Congo Craton, by which time modern-day plate tectonic processes were already in operation (e.g. Bastow et al. 2011 ;Palin et al. 2020 ). ...
The Central African Plateau comprises a mosaic of numerous Archean terranes — the Congo, Bangweulu and Kalahari cratons — sutured in a series of Proterozoic to early Cambrian orogenic events. Major upper-crustal deformation and complex craton margin fault zones reflect the region’s diverse tectonic history: rifting during the Neoproterozoic, collision during the Pan-African Orogeny, and more recently, Permo-Triassic Karoo rifting and the Pliocene development of the Southwestern branch of the East African Rift. The tectonic evolution and extent to which the lithospheric mantle has been reworked by each tectonic event is poorly understood. New seismograph networks across the Plateau provide fresh opportunity to place constraints on the plate-scale Precambrian-to-Phanerozoic processes that have acted across the region. Utilising data from seismograph deployments across the Central African Plateau, including the new Copper Basin Exploration Science (CuBES) network — a NW–SE-trending, 750km–long profile of 35 broadband stations — we explore lithospheric deformation fabrics associated with past and present tectonic events via a shear-wave splitting study of mantle seismic anisotropy. Results reveal short length-scale variations in splitting parameters (fast direction: φ, delay time: δt), suggestive of a fossil lithospheric fabric cause for the observed anisotropy. A lack of fault-parallel φ across the Mwembeshi Shear Zone, suggests it may be too narrow at mantle depths, a thin-skinned, crustal-scale feature, and/or did not experience sufficient fault parallel shear-strain during its last active phase to form a lithospheric deformation fabric discernible via teleseismic shear-wave splitting. In the heart of the Lufilian Arc, we observe abrupt changes in splitting parameters with NE–SW, N–S and NW–SE φ and 0.5 s<δt<1.2 s evident at short length-scales: no single, uniform, anisotropic LPO fabric defines the entire region. This is consistent with the view that multiple episodes of deformation shaped the Lufilian Arc, or perhaps that pre-existing fabrics, relating to Neoproterozoic Katangan Basin development, have failed to be completely overprinted by the Pan-African Orogeny. Near the Domes, where most intense crustal re-working is thought to have taken place during the Pan-African Orogeny, there is a cluster of null and low δt splits which likely reflects the lack of organised LPO fabrics, perhaps due to the presence of depth-dependent anisotropy. The neighbouring Congo Craton margin is marked by consistently weak anisotropy (δt<0.7 s) indicating a weak horizontal alignment of olivine at mantle lithospheric depths, typical of several Archean terranes worldwide.
... Considering these pieces of evidence, Wang et al. (2024) advocated an early Neoarchean geodynamic transition from vertical mantle plume-dominated geodynamics to a subsequent regime dominated by horizontal motion associated with plate tectonics within the North China Craton. This interpretation aligns with a global perspective that the global onset of plate tectonics occurred during the late Mesoarchean/ early Neoarchean based on the progressive establishment of a worldwide network of subduction zones at that time (Dhuime et al., 2012;Palin and Santosh, 2021;Palin et al., 2020;Tang et al., 2016). Subsequently, the coexistence of the early Neoarchean plume-related tholeiitic-komatiitic rocks and subduction-related calc-alkaline rocks has been widely identified in many terranes, such as Abitibi-Wawa, Canada (Polat, 2009;Wyman et al., 2002); Veligallu, India (Dey et al., 2018); and Youanmi, Western Australia (Wyman and Kerrich, 2012). ...
Identifying the processes responsible for the generation and evolution of the Archean continental crust is crucial for understanding the tectonic regimes present on early Earth. A major episode of continental growth during the early Neoarchean has been identified in many cratons worldwide. Indeed, early Neoarchean magmatism has been recognized in several terranes within the North China Craton over the past decade, although the geodynamic regime in which such activity occurred remains highly debated. Here, we focus on newly recognized early Neoarchean mylonitic trondhjemite and granodiorite from the southern Jilin terrane, China, to address this knowledge gap. Zircon U-Pb geochronology reveals that these granitoids formed at ca. 2.7 Ga. They display adakitic geochemical characteristics, such as high Sr/Y and LaN/YbN ratios. Their low MgO, Cr, and Ni contents, along with low δ18O values (4.19‰−5.39‰) and positive εHf(t) (0.7−6.5) and εNd(t) (2.0−2.6) values, indicate that they originated from thickened juvenile lower continental crust. Thermodynamic modeling further constrains the ca. 2.7 Ga granitoids to have been generated from partial melting driven by amphibole breakdown under granulite-facies P-T conditions of 10−15 kbar and 800−900 °C, with garnet and amphibole as the major residual minerals. Combined with previous studies, we suggest that the North China Craton underwent significant crustal growth during the early Neoarchean, which was likely attributed to the synergistic effects of waning mantle plume activity and the coeval onset of plate tectonics.
... While slabs may melt to small or even moderate degrees along modern subduction zone thermal regimes (72,73), our results point to much larger degrees of melting during the Proterozoic, a time when plate tectonics likely resembled modern regimes, but the upper mantle was hotter [e.g., (74,75)]. This could explain a longstanding mystery about massif-type anorthosites: their restriction to the middle part of Earth's history. ...
... If slab melting made massif-type anorthosites, then their production should have declined as the mantle cooled and oceanic crust in subduction zones melting thoroughly enough to produce basaltic magmas became rare or ceased entirely. The absence of massif-type anorthosites older than the Neoarchean may be the result of a different style of tectonics [e.g., (75,76)] or of differences in plate thickness, temperature, and/or velocity (4,5). Any one of these factors would likely affect the mechanics of convergent margins and the feasibility of long-lived mafic magma systems at approximately Moho depths with lifetimes long enough to segregate large plagioclase cumulate accumulations. ...
Massif-type anorthosites, enormous and enigmatic plagioclase-rich cumulate intrusions emplaced into Earth’s crust, formed in large numbers only between 1 and 2 billion years ago. Conflicting hypotheses for massif-type anorthosite formation, including melting of upwelling mantle, lower crustal melting, and arc magmatism above subduction zones, have stymied consensus on what parental magmas crystallized the anorthosites and why the rocks are temporally restricted. Using B, O, Nd, and Sr isotope analyses, bulk chemistry, and petrogenetic modeling, we demonstrate that the magmas parental to the Marcy and Morin anorthosites, classic examples from North America’s Grenville orogen, require large input from mafic melts derived from slab-top altered oceanic crust. The anorthosites also record B isotopic signatures corresponding to other slab lithologies such as subducted abyssal serpentinite. We propose that anorthosite massifs formed underneath convergent continental margins wherein a subducted or subducting slab melted extensively and link massif-type anorthosite formation to Earth’s thermal and tectonic evolution.
... The fabric of Earth's present-day outer lithospheric shell directly reflects modern-style plate tectonics (Kious and Tilling, 1996). An evergrowing geological database suggests that this tectonic regime has not operated throughout Earth's history (Hawkesworth and Brown, 2018;Palin et al., 2020). Geologic evidence indicates that the first two billion years of Earth's history (Hadean and Archean eons, 4.5-2.5 Ga) were dominated by one or more different styles of tectonic regimes compared to today that likely evolved in multiple stages and that these changes were not abrupt but transitional and overlapping in both space and time (c.f., Cawood et al., 2022; Table 1). ...
... Whilst evidence for the 'onset of plate tectonics' has thus naturally been destroyed, mounting evidence based on a range of geochemical proxies (Cawood and Hawkesworth, 2019;Dhuime et al., 2012;Keller and Schoene, 2012;Nebel-Jacobsen et al., 2018;Palin et al., 2020) indeed marks this transition, with a crustal average chemical composition slowly changing though time between 2.9-2.5 Ga indicating this slow process. With progressive evidence for rock associations consistent with a subduction zone (or convergent plate margin) setting towards the late Archean, it seems plausible to ascribe "the onset of sustained subduction" to a global domino effect, in which larger, connected subduction leads towards a network of plate boundaries. ...
Subduction is a key geodynamic feature on modern Earth that drives crustal chemical diversity, bridging the atmo-, hydro-, and lithosphere, but remains an enigmatic, unique planetary feature. Indisputable is the critical role of subduction in shaping Earth's geomorphology and crustal dichotomy (ocean vs continental crust) and its impacts on long-term climate, making it arguably the most important process on present-day Earth across all geosciences. It is thus important to understand to what degree, or if at all, subduction was operational during the billions of years that led to our geological status quo. Here, we assess the feasibility of Archean subduction with a focus on early Earth geodynamics. We argue that convection-driven rifting, but not spreading, formed the first keels under the primordial crust, providing the necessary stability for crustal survival. These sections of crustal rejuvenation would counterintuitively forge the first stable proto-cratonic terranes, which later evolved into cratons. Hydrated upper crustal rocks were vital in generating early fluxed mantle melting and related volcanism, but also for partial melting in hydrated lower crustal sections within proto-cratons, giving rise to tonalite-trondhjemite granodiorites (TTGs). Both processes operated off-and on-craton, respectively, and required melting of hydrated crust and crustal convergence but are unrelated. Away from proto-cratonic regions of minor episodic divergence and rifting, relative motions were accommodated by convergence and shuffle tectonics, leading to Archean-style subduction in localised regions that were prone to destruction. This primitive form of subduction and crustal maturation has operated from the earliest Archean time in a plate-and-lid regime. Crucially, this 'Archean subduction' represents short-lived crustal shuffle-tectonics outside areas of today's cratons with fluxed melting in upper mantle regions but does not resemble present-day Benioff-style subduction. The development of subduction akin to present-day processes towards the end of the Archean could plausibly have driven atmospheric oxygenation over a few hundred million years between ca. 2.8-2.3 Ga, with H-loss to space accompanied by atmospheric oxidation through subduction-related global volcanic SO 2 emissions.
