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Geodynamics of kimberlites on a cooling Earth: Clues to plate tectonic evolution and deep volatile cycles
Abstract
Kimberlite magmatism has occurred in cratonic regions on every continent. The global age distribution suggests that this form of mantle melting has been more prominent after 1.2 Ga, and notably between 250–50 Ma, than during early Earth history before 2 Ga (i.e., the Paleoproterozoic and Archean). Although preservation bias has been discussed as a possible reason for the skewed kimberlite age distribution, new treatment of an updated global database suggests that the apparent secular evolution of kimberlite and related CO2-rich ultramafic magmatism is genuine and probably coupled to lowering temperatures of Earth's upper mantle through time. Incipient melting near the CO2- and H2O-bearing peridotite solidus at >200 km depth (1100–1400 °C) is the petrologically most feasible process that can produce high-MgO carbonated silicate melts with enriched trace element concentrations akin to kimberlites. These conditions occur within the convecting asthenospheric mantle directly beneath thick continental lithosphere. In this transient upper mantle source region, variable CHO volatile mixtures control melting of peridotite in the absence of heat anomalies so that low-degree carbonated silicate melts may be permanently present at ambient mantle temperatures below 1400 °C. However, extraction of low-volume melts to Earth's surface requires tectonic triggers. Abrupt changes in the speed and direction of plate motions, such as typified by the dynamics of supercontinent cycles, can be effective in the creation of lithospheric pathways aiding kimberlite magma ascent. Provided that CO2- and H2O-fluxed deep cratonic keels, which formed parts of larger drifting tectonic plates, existed by 3 Ga or even before, kimberlite volcanism could have been frequent during the Archean. However, we argue that frequent kimberlite magmatism had to await establishment of an incipient melting regime beneath the maturing continents, which only became significant after secular mantle cooling to below 1400 °C during post-Archean times, probably sometime shortly after 2 Ga. At around this time kimberlites replace komatiites as the hallmark mantle-derived magmatic feature of continental shields worldwide. The remarkable Mesozoic–Cenozoic ‘kimberlite bloom’ between 250–50 Ma may represent the ideal circumstance under which the relatively cool and volatile-fluxed cratonic roots of the Pangea supercontinent underwent significant tectonic disturbance. This created more than 60% of world's known kimberlites in a combination of redox- and decompression-related low-degree partial melting. Less than 2% of world's known kimberlites formed after 50 Ma, and the tectonic settings of rare ‘young’ kimberlites from eastern Africa and western North America demonstrate that far-field stresses on cratonic lithosphere enforced by either continental rifting or cold subduction play a crucial role in enabling kimberlite magma transfer to Earth's surface.
... Kaaroo large igneous province extrusion is of 182 Ma age and is associated with the Gondwana breakup (Riley et al., 2006). The Kaapvaal Craton is punctuated by kimberlites after 1.8 Ga with peak kimberlite magmatic activity at 90 ± 10 Ma which was significant even at 60 ± 10 Ma (Tappe et al., 2018). The micaceous Group II kimberlites (reclassified as carbonate-rich olivine lamproites-CROL by Pearson et al., (2019)) are > 110 Ma in age, whereas Group I or archetypal kimberlites are of 100 Ma age (Kobussen et al., 2009). ...
... The Matsoku kimberlite is a small, elliptical diatreme (90 x 35 m) located in northern Lesotho. It intruded the Karoo supergroup Stormberg lavas at 94.7 Ma (Olive et al., 1997;Tappe et al., 2018). Matsoku kimberlite is a barren kimberlite representing single magmatic phases (Cox et al., 1973). ...
... The Thaba Putsoa kimberlite is a diamond barren kimberlite with an age of 89 Ma situated in the mountains in northern Lesotho (Tappe et al., 2018). It contains different types of xenoliths including granular spinel lherzolite, granular graphite-bearing garnet-spinel harzburgite, sheared porphyroclastic dunite, etc. (Boyd and Nixon, 1975). ...
Nominally anhydrous mantle minerals (olivine, pyroxenes, garnets, etc.) in 11 peridotite xenoliths from four different uneconomic and economic Kaapvaal Craton kimberlite pipes (Matsoku, Thaba Putsoa, Pipe200 and Bultfontein) have been investigated using Fourier transform infrared spectroscopy (FTIR). Allxenoliths contain accessories of garnet, diopside, chromite, and phlogopite. High orthopyroxene content(>30 mol vol.%) in most xenoliths from all kimberlites and its interconnected channel-like nature hint towards hydrous siliceous fluid metasomatism. Peridotite xenoliths from uneconomic kimberlites show development of phlogopite and clinopyroxene (– chromite) forming veins and in garnet rims suggesting metasomatism by alkaline silico-carbonatite (possibly kimberlite-related) melt. The xenoliths contain significant H2O in olivine (17–62 ppm), orthopyroxene (21–230 ppm), and clinopyroxene (87–833 ppm), whereas garnets are dry and only show IR absorbance bands at > 3,670 cm-1 for contamination of hydrous minerals. Compared to the economic kimberlites in the Kaapvaal Craton, the uneconomic kimberlite xenoliths from this study have lower orthopyroxene and olivine H2O content. In the xenoliths affected by garnet breakdown metasomatism, the H2O content of orthopyroxene and olivine is higher and lower, respectively. The structural hydroxyl distribution profile across olivine and higher inter-mineral water partition coefficient, suggest diffusion of hydrogen and possible re-equilibration. Statistical analysis of the olivine spectra suggests that hydrogen bands at 3540, 3624, 3638, and3672 cm-1 are a good discriminant of economic and uneconomic kimberlites and in literature, they are associated with metasomatism, weathering-associated processes, high water activity, and oxygenfugacity. The lower water concentration in xenoliths from uneconomic kimberlite from the margin of the craton than the economic kimberlites from the interior of the Kaapvaal Craton and identified metasomatism hints towards dehydration of xenoliths by water-poor and CO2-rich melts in tectonized cross-lithospheric zones causing diamond resorption and may be responsible for the diamond-poor nature of uneconomic kimberlites in northern Lesotho.
... Kimberlites are widely distributed across different cratons worldwide, and despite their widespread occurrence through time they have relatively homogenous mineralogical and geochemical compositions (Kjarsgaard et al., 2009;Tappe et al., 2018). On the other hand, orangeites have been found to occur only on the Kaapvaal craton as a distinctive variety of lamproite magmatism (Mitchell, 1995). ...
... The orangeite has a 40 Ar/ 39 Ar phlogopite age of ca. 155 Ma (Tappe et al., 2018), and intruded the Archaean Meinhardskraal granite and a dolerite dyke. The M1 pipe comprises both coherent magmatic and volcaniclastic orangeite varieties. ...
... The M1 pipe comprises both coherent magmatic and volcaniclastic orangeite varieties. The diamond reserves exploited until 2000 were sourced from the high-grade M1 pipe (1.9 carats per tonne; Tappe et al., 2018), which was overlain by a high-grade surface enrichment zone (Field et al., 2008). For this study, we sampled mineral concentrate from operations that reprocessed the historical M1 and M8 orangeite tailings in 2019. ...
... To test whether the supercontinent cycle is the first-order mechanism of plate tectonics evolution, global geological datasets (GGDs) have been compiled and investigated. Six key archives of Earth's history were collected (Brown and Johnson, 2018;Liu et al., 2022;Mulder and Cawood, 2021;Puetz and Condie, 2019;Tappe et al., 2018). They represent global datasets with abundant geological data spanning more than 3 billion years of Earth's evolution. ...
... The six GGDs are composed of data from carbonatite, zircon hafnium, kimberlite, metamorphism, monazite and zircon records (Brown and Johnson, 2018;Liu et al., 2022;Mulder and Cawood, 2021;Nance et al., 2022;Puetz and Condie, 2019;Tappe et al., 2018). For comparison purposes, each dataset is carefully classified and shown in histograms of 50 Myr bins from 0 to −3000 Myr (Figs. 2 and 3). ...
... The monazite archive is taken from Mulder and Cawood (2021) and is a large and global dataset representative of Earth's tectono-thermal history but has Table 1 Cross table of Spearman's correlation index for the 6 GGDs of this study with the respective p values with student's t-tests (*** corresponds to significance at 1%). (Mulder and Cawood, 2021;Puetz and Condie, 2019). (b) Datasets for carbonatite, kimberlite and metamorphic archives (Brown and Johnson, 2018;Liu et al., 2022;Tappe et al., 2018). Supercontinent cyclicities (Sc 500, Sc 600, Sc 800 and Sc Acc) are also shown with arrows toward their considered assembly timings (i.e., Broussolle, 2022) (K, C, R, G, P, E = Kenorland, Columbia, Rodinia, Gondwana (Pannotia), Pangea and Eurasia). ...
Whether the supercontinent cycle (Sc) is the major process driving plate tectonics evolution has not been purposely investigated. If true, it would result in more geological records formed during each supercontinent assembly. In this study, a quantitative statistical approach is used to investigate this question. Six global geological datasets (GGDs) of carbonatite, zircon hafnium, kimberlite, metamorphism, monazite and zircon records are analyzed using Spearman’s correlation (ρs). Ranking the GGDs according to Spearman’s method allows them to be compared. Each GGD shows moderate to very strong correlations (0.5<ρs<0.9), with the metamorphism, monazite, zircon and zircon hafnium datasets displaying the most similarities. Each published supercontinent cyclicity (Sc 500 Myr, Sc 600 Myr, Sc 800 Myr and Sc acceleration) is then depicted according to its assembly timing. A second Spearman correlation performed with the four supercontinent cyclicities suggests that the Sc acceleration hypothesis best fits the geological archives (average ρs=0.45), potentially supporting the supercontinent cycle as the first-order mechanism of plate tectonics evolution. Conversely, constant cyclicities result in weaker correlations (average ρs<0.26), which could indicate significant decoupling of the geological archives and the supercontinent cycle. Moreover, Sc 600 surprisingly shows no correlation with the six GGDs (average ρs=0.04). The implications for the supercontinent cycle and the limits of Spearman’s correlation are also discussed.
... The Labrador coast on the North Atlantic Craton (NAC) is a representative occurrence where a sequence of alkaline rocks was emplaced over more than 1200 Ma: lamproites were emplaced in the Mesoproterozoic and carbonate-bearing rocks since the Late Neoproterozoic (Fig. 1a) 17 . The rise of carbonate-bearing magmas since the Late Neoproterozoic in Labrador is consistent with a significant increase in the abundance of carbonatites and kimberlites globally over the past 700 Myr 18,19 (Fig. 1d). This Aillik Bay locality in Labrador experienced three magmatic pulses: lamproites at ca. 1.4 Ga, CO 2 -rich ultramafic lamprophyres and carbonatites at 590-555 Ma, and silicaundersaturated nephelinites and melilitites at 142 Ma (Fig. 1a). ...
... Cu isotopes ( 63 Cu and 65 Cu) have been widely applied to trace redox reaction processes because significant Cu isotopic variation can occur during oxidation-reduction reactions 22 42 , and kimberlites 18 . The cumulative U-Pb age data for detrital zircons interpreted to originate from carbonatite-alkaline rocks in Neoproterozoic-Triassic sandstones from Antarctica (red line, n = 493) 43 and the C-O-H species in their mantle sources 13,14 are also shown. ...
... However, the exact timing of the oxidation of the cratonic roots is poorly constrained because it is difficult to date the carbonatite metasomatism event seen in these peridotite xenoliths. We compiled the global age distribution of nonorogenic lamproites (Supplementary Data 1), kimberlites 18 , and carbonatites 42 to decode carbonatite activity in the mantle (Fig. 1c, d). Carbonatites (defined as containing >50% carbonate minerals) and kimberlites show a marked crescendo from the Neoproterozoic onwards 42 . ...
The oxygen fugacity (fO2) of the lower cratonic lithosphere influences diamond formation, melting mechanisms, and lithospheric evolution, but its redox evolution over time is unclear. We apply Cu isotopes (δ⁶⁵Cu) of ~ 1.4 Ga lamproites and < 0.59 Ga silica-undersaturated alkaline rocks from the lithosphere-asthenosphere boundary (LAB) of the North Atlantic Craton to characterize fO2 and volatile speciation in their sources. The lamproites’ low δ⁶⁵Cu (−0.19 to −0.12‰) show that the LAB was metal-saturated with CH4 + H2O as the dominant volatiles during the Mesoproterozoic. The mantle-like δ⁶⁵Cu of the < 0.59 Ga alkaline rocks (0.03 to 0.15‰) indicate that the LAB was more oxidized, stabilizing CO2 + H2O and destabilizing metals. The Neoproterozoic oxidation resulted in an increase of at least 2.5 log units in fO2 at the LAB. Combined with previously reported high fO2 in peridotites from the Slave, Kaapvaal, and Siberia cratonic roots, this oxidation might occur in cratonic roots globally.
... Using this approach, a large dataset for Other kimberlite and lamproite locations and cratonic domains referred to in the main text are shown for orientation (modified after Jelsma et al., 2018). Geographic coordinates and emplacement ages for the kimberlite clusters shown are summarized in Tappe et al. (2018b). mantle-derived xenocrysts and micro-xenoliths from cratons worldwide has been produced and improved our understanding of ancient CLM and its diamond potential (e.g. ...
... The emplacement age of the Nxau Nxau kimberlites (ca. 84 Ma; Farr et al., 2018) overlaps with the prominent Late Cretaceous peak of kimberlite magmatic activity across southern Africa and Brazil (Griffin et al., 2014;Tappe et al., 2018b), probably in response to plate reorganization during the late phase of the West Gondwana breakup. The Nxau Nxau kimberlites typically consist of olivine macrocrysts (mostly altered) set in a fine-grained groundmass of olivine, spinel, perovskite, apatite, phlogopite, calcite and serpentine (Farr et al., 2018), i.e. a typical hypabyssal Group-1 kimberlite mineral assemblage and texture (Mitchell, 2008). ...
... Below, we compare lithospheric mantle sections reported from the more central parts of the Congo craton at Mbuji Mayi (and Tshibwe) in the D.R. Congo and Catoca in Angola with the CLM architecture at the southern margin of the Congo craton in NW Botswana (this study). We note that these reconstructed CLM sections were probed by relatively young kimberlite magmatism during the Cretaceous between ca. 120 and 70 Ma (Robles-Cruz et al., 2012;Farr et al., 2018;Tappe et al., 2018b). Whereas the lithosphere was in excess of 200 km thick beneath the central Congo craton, with extensive metasomatic overprinting at its base (Batumike et al., 2009;Ashchepkov et al., 2012;Kosman et al., 2016;Korolev et al., 2021), our findings from the southern craton margin suggest the presence of a 145-km-thick lithosphere, with a thick and heavily overprinted lithosphere-asthenosphere transition zone down to 210 km depth (Figs 9 and 10). ...
The continental lithospheric mantle (CLM) beneath the southern margin of the Congo craton has remained elusive mainly because of thick Phanerozoic sedimentary cover concealing possible kimberlite and lamproite diatremes. In this study, we explore this lithospheric mantle section by using major and trace element compositions of mantle-derived clinopyroxene and garnet xenocrysts from kimberlites of the ca. 84 Ma Nxau Nxau cluster in NW Botswana, which is part of the poorly known Xaudum kimberlite province extending into northern Namibia. We utilize these data to better understand the thermal and compositional evolution of the lithospheric mantle at the southern margin of the Congo craton. The clinopyroxene population (83 individual grains) comprises Cr-rich and Cr-poor diopsides with variable major (Al2O3, Na2O, Mg#) and incompatible trace element (U, Th, Zr, Hf, Nb, Ta, REEs) compositions. The large garnet population studied (496 individual grains) is dominated by lherzolitic G9 (38%) and `megacrystic´ G1 (41%) compositions, with minor contributions from Ti-metasomatized G11 (7%) and eclogitic G3 (6%) cratonic mantle sources. Harzburgitic G10 garnet is very rare (two grains only), consistent with a lherzolite-dominated CLM section in a craton margin position. The eclogitic garnet population has compositions akin to garnet from high-Mg cratonic mantle eclogite xenoliths, and such compositions have recently been interpreted as metasomatic in origin within the mantle xenoliths literature.
Pressure–temperature calculations using the single-grain clinopyroxene technique reveal a relatively cold cratonic geotherm of 37-38 mW/m2 for the study region during the Late Mesozoic. For peridotitic garnets, projections of calculated Ni-in-garnet temperatures onto the independently constrained regional conductive geotherm suggest that lherzolite dominates at <145 km depths, whereas high-Ti lherzolitic G11 garnets and `megacrystic´ G1 garnets originate mostly from greater depths, down to the lithosphere base at 150 to 210 km depth. The apparent confinement of ´megacrystic´ G1 garnet to the bottom of the lithosphere suggests formation from infiltrating asthenosphere-derived proto-kimberlite liquids during melt–rock interactions. In general, the data suggest that the CLM beneath NW Botswana is depleted to about 145 km depth, and between 145-210 km depths a thick metasomatized layer is identified, representing the transition into the underlying asthenosphere. A relatively thin lithosphere beneath NW Botswana is consistent with the proposed craton margin setting, especially when compared to the thicker cratonic roots beneath the central regions of the Congo and Kalahari cratons in Angola and South Africa, respectively, reaching down to 250 km depth and possibly even deeper.
The compositional dissimilarity between the deepest-derived garnets from kimberlites in NW Botswana (i.e., from the diamond stability field) and garnets that occur as inclusions in diamond from cratons worldwide suggests extensive overprinting of the lowermost cratonic lithosphere by oxidative melt-related metasomatism. This finding, together with the very low diamond grades of the Xaudum kimberlites, points to a diminished diamond potential of the large and mostly unexposed ‘cratonic’ region (e.g., covered by thick desert sand) located between the major diamond mining districts of the Congo craton to the north (e.g., Catoca) and the Kalahari craton to the south (e.g., Orapa and Jwaneng).
... Collisional settings can trigger tectonic disturbances beneath cratons that lead to the ascent of kimberlite magmas (e.g., Premier kimberlite; Tappe et al., 2020). Similarly, extensional processes involving during rifting and re-organization of lithospheric plates may also play an important role in kimberlite magmatism (Jelsma et al., 2009;Tappe et al., 2018;Gernon et al., 2023;Takenaka et al., 2023). ...
... The age distribution of global kimberlite magmatism displays a periodicity that is inferred to be closely associated with the supercontinent cycle and reflects the Earth's tectonothermal evolution (Jelsma et al., 2009;Tappe et al. 2018;Liu et al., 2023). Available geochronological data show that volatile-rich kimberlite magmatism increased after the Mesoproterozoic (ca. ...
... Available geochronological data show that volatile-rich kimberlite magmatism increased after the Mesoproterozoic (ca. 1.2 Ga), supporting the notion of a secular cooling of the lithospheric mantle (e.g., Tappe et al., 2018) and suggesting the addition of CO 2 and H 2 O to the mantle by deep and cold subduction (Stern et al., 2016;Liu et al., 2023). ...
Kimberlite magmatism provides insights into periodic tectonothermal processes linked to the evolution of supercontinents. Paleozoic and Mesozoic kimberlites overlapping with the Pangea cycle are exposed in the Amazonian Craton (Pimenta Bueno field) and the Neoproterozoic Brasília Belt. Phlogopite in mantle xenoliths in kimberlites from the Amazonian Craton are characterized by low Cr2O3 (< 1 wt. %) and an enrichment in TiO2 (> 2 wt. %), akin to secondary phlogopite formed by kimberlite magma infiltration in the mantle. Low Ti-Cr (< 1 wt. %) and high #Mg (91–92) grains are linked to extensive metasomatism of garnet peridotites resulting in clinopyroxene-phlogopite rocks. In situ phlogopite Rb-Sr isochron ages of 250–220 Ma constrain the emplacement of pipes in the Amazonian Craton with no age difference between distinct phlogopite compositions (higher and lower TiO2 phlogopite) and microstructures (porphyroclasts, neoblasts, reaction rims). Mantle xenoliths in kimberlite pipes from the Brasília Belt present high TiO2 (> 2 wt. %) akin to secondary phlogopite formed by magma infiltration, and low Ti-Cr (1 wt. %), and high #Mg (> 92) phlogopite akin to primary grains in equilibrium with garnet. In situ phlogopite Rb-Sr isochron ages from all Brasília Belt phlogopite types span 90–80 Ma, constraining the emplacement of diamondiferous and barren pipes, with no relic of older metasomatic events. The kimberlites from the Pimenta Bueno field (Amazonian Craton) are coeval with the beginning of the extension within Pangea that culminated with the Central Atlantic rifting. In fact, the Permian-Triassic kimberlites occur close to intracratonic basins that are crosscut by ca. 200 Ma dykes and sills of the Central Atlantic Magmatic Province. In situ phlogopite Rb-Sr isochron ages spanning 90–80 Ma in the pipes from central and southeastern Brazil (Brasília Belt) may be associated with propagation of far-field stresses linked to opening of the South Atlantic Ocean during the Pangea break-up.
... Kimberlite is a highly carbonaceous volcanic rock (e.g., CO 2 ~ 20 wt% solubility in the magmatic melt 51 ), and kimberlite eruptions have a high ability to emit greenhouse gases 52 . Since the peak of the kimberlite formation occurred during the Cenomanian to Turonian (100-90 Ma) 53 , these volcanic events may have contributed to the CTM. Indeed, Patterson and Francis 52 have suggested that kimberlite formation triggered early Cenozoic hyperthermal events. ...
... Indeed, Patterson and Francis 52 have suggested that kimberlite formation triggered early Cenozoic hyperthermal events. Although kimberlite exhibit high Os concentration (~ 0.03 to 8 ppb) 54 , it is composed of the cluster of small pipes (~ 10 ha) 53 and its total volume is not significant enough to alter seawater PGE cycles. Therefore, we consider that the input of unradiogenic PGEs into the ocean through the weathering of kimberlite bodies was insignificant. ...
... . Ages of the Madagascar Flood Basalt Province are from Refs.13,[18][19][20] . The ages of the kimberlite formation are based on Ref.53 . The ages of Japanese granitoid are from Ref.48 . ...
The Turonian age (~ 90–94 Ma) was the hottest geological interval in the Cretaceous and also marked by the K3 event, a pronounced enrichment of ³He in pelagic sediments (i.e., massive input of extraterrestrial materials). Here, we present Os isotopic (¹⁸⁷Os/¹⁸⁸Os) and platinum group element (PGE) data from Turonian sedimentary records. After a sharp unradiogenic shift during the end-Cenomanian oceanic anoxic event 2, the ¹⁸⁷Os/¹⁸⁸Os ratios declined continuously throughout the Turonian, which could be ascribed to the formations of several large igneous provinces (LIPs). Because the interval with the most unradiogenic ¹⁸⁷Os/¹⁸⁸Os ratios (i.e., enhanced LIP volcanism) does not correspond to the warmest interval during the mid-Cretaceous, additional sources of CO2, such as subduction zone volcanism or the kimberlite formation, may explain the Cretaceous Thermal Maximum. As Os isotope ratios do not show any sharp unradiogenic shifts and PGE concentrations do not exhibit a pronounced enrichment, an influx of fine-grained cosmic dust to the Earth’s surface, possibly from the long-period comet showers, can be inferred at the time of the ³He enrichment during the mid-Turonian K3 event. Our findings highlight the different behaviors of ³He and PGE information in the sedimentary rocks during the input of fined-grained extraterrestrial materials.
... The global kimberlite record suggests that approximately 80% of known occurrences are linked to breakup stages of supercontinents, and the others are collision-induced (Jelsma et al., 2009;Tappe et al., 2018;Zhang et al., 2019). The Indian Ocean was a stepwise breakup of east and west Gondwana at 157 Ma, and a breakup of east Gondwana at 130 Ma (Gnos and Perrin, 1996), which is registered only in the Batain Basin of Oman . ...
... So it appears that the emplacement of the Early Cretaceous kimberlite and carbonatite magmatism (~140 Ma) in Oman is related to the breakup of Gondwana, and kimberlite and carbonatite occurred during the opening of the Indian Ocean (Peters and Mercolli, 1998). The most critical petrological variables enabling the formation of kimberlite and CO 2 -rich ultramafic magmatism are the availability of oxidized CHO volatile species such as CO 2 and H 2 O (Yaxley et al., 2017), as well as the lower temperatures of Earth's upper mantle (Green and Falloon, 1998;Tappe et al., 2018). Thus, the breaking up of Gondwana, which releases pressure, provided a relatively cool and volatile-fluxed circumstance for the formation of Oman kimberlite and carbonatite melts. ...
... Mesozoic-Cenozoic kimberlite between 250 Ma and 50 Ma is the most remarkable kimberlite bloom globally, and more than 60% of the world's known kimberlite clusters on every continent were emplaced during this bloom. It was observed that 140 Ma-130 Ma is one of the strongest global kimberlite abundance peaks of this bloom (Figure 8 in Tappe et al., 2018), which corresponds to the period of the Pangea supercontinent breakup (Jelsma et al., 2009). By that time, the Indian Ocean had opened widely and the Gondwana portion of Pangea was separated into West and East Gondwanaland. ...
Northeastern Oman is characterized by carbonatite and kimberlite complexes, which are the ideal samples for studying the relationship between carbonatite and kimberlite. However, the ages of the Oman kimberlite and carbonatite complexes are still unknown, which restricts the understanding of the relationship between carbonatite and kimberlite in Oman. In this study, we use in situ laser ablation inductively coupled plasma mass spectrometry (LA-ICPMS) to analyze the apatite from Oman carbonatite, kimberlite, and spessartite. The U–Pb apatite ages are 141.6 ± 6.0 Ma, 137.4 ± 5.2 Ma, and 141.2 ± 6.2 Ma for carbonatite, spessartite (a kind of calc-alkaline lamprophyre), and kimberlite, respectively. These results suggest that the carbonatite and kimberlite were emplaced contemporaneously, followed by calc-alkaline carbonatite (spessartite) emplaced in the Early Cretaceous. The occurrence of carbonatite, kimberlite, and spessartite magmatism of Oman was contemporaneous with the time of the Gondwana breakup during the opening of the Indian Ocean. It is seen that 140 Ma–130 Ma is one of the strongest global kimberlite abundance peaks of the 250 Ma–50 Ma kimberlite bloom, which corresponds with the period of the Pangea supercontinent breakup. The Oman kimberlites and carbonatites are related to a distal effect of the breakup of the Gondwana portion of the Pangea supercontinent, which provided a cool, volatile-fluxed decompression-related circumstance for the formation.
... Lithospheric extension in, or adjacent to, Archean cratons during continental rifting has previously been recognized as a mechanism for emplacement of kimberlites, lamproites and other related volatile-and incompatible element-enriched ultramafic diatremes [38][39][40][41][42] 45,46 ), amongst many others. However, the role of (super)continental breakup has only recently begun to be significantly appreciated for kimberlite emplacement during periods of continental breakup 2,38,42 . ...
... However, the role of (super)continental breakup has only recently begun to be significantly appreciated for kimberlite emplacement during periods of continental breakup 2,38,42 . In all breakup-related cases, diatreme emplacement appears to be contemporaneous with breakup, but with a peak production of volatile-rich ultramafic rocks lagging behind the breakup period 41,42 . The same applies to Argyle and Nuna breakup. ...
... Thus, there appears to be a first-order control of continental extension and plate velocities on (diamondiferous) kimberlite and related volatile-rich ultramafic diatreme production 41 . ...
Argyle is the world’s largest source of natural diamonds, yet one of only a few economic deposits hosted in a Paleoproterozoic orogen. The geodynamic triggers responsible for its alkaline ultramafic volcanic host are unknown. Here we show, using U-Pb and (U-Th)/He geochronology of detrital apatite and detrital zircon, and U-Pb dating of hydrothermal titanite, that emplacement of the Argyle lamproite is bracketed between 1311 ± 9 Ma and 1257 ± 15 Ma (2σ), older than previously known. To form the Argyle lamproite diatreme complex, emplacement was likely driven by lithospheric extension related to the breakup of the supercontinent Nuna. Extension facilitated production of low-degree partial melts and their migration through transcrustal corridors in the Paleoproterozoic Halls Creek Orogen, a rheologically-weak rift zone adjacent to the Kimberley Craton. Diamondiferous diatreme emplacement during (super)continental breakup may be prevalent but hitherto under-recognized in rift zones at the edges of ancient continental blocks.
... Since the Mel kimberlites are also petrographically and geochemically similar to other Melville Peninsula kimberlites, this kimberlite activity is likely an extension of the same type of magmatism that reflects deep lithospheric disturbances of thick, cratonic lithosphere, allowing small-degree melts from the asthenosphere to intrude and, in some cases, hybridize with the local lithosphere. Tappe et al. (2018) suggest a model where kimberlite magmatism along present-day eastern Canada and western Greenland is triggered by the breakup of Rodinia. Furthermore, Sarkar et al. (2018) suggested that eruption of kimberlites and related rocks in the Neoproterozoic to Cambrian on the Melville Peninsula is evidence for the breakup of Rodinia in this area and the formation of the Iapetus Ocean. ...
... In areas of thinner and non-cratonic lithosphere, the thermal regime of Iapetus rifting produced basaltic and granitic magmatism (Kamo and Gower 1994;Ernst and Buchan 2004;Robert et al. 2021;Wall et al. 2021;Dalton et al. 2022). We note that the timing and location of the Mel kimberlites support the model outlined in Tappe et al. (2018) and Sarkar et al. (2018). ...
Diamond exploration on the Melville Peninsula has uncovered a slew of Neoproterozoic to Cambrian aged kimberlites and related magmas. Drilling by North Arrow Minerals Inc. in 2018 at the Mel property, located 100 km southwest of Hal Beach, Nunavut, Canada, delineated dikes and sills, logged as kimberlite. Phlogopite, ilmenite, and spinel compositions and whole-rock major and trace element abundances indicate that the Mel dikes are archetypal kimberlites. A Rb-Sr isochron for phlogopite yielded 555.6 ± 2.7 Ma, interpreted as the age of emplacement of the Mel kimberlites, with an initial ⁸⁷Sr/⁸⁶Srinitial ratio of 0.7044. This age is similar to other Neoproterozoic to Cambrian kimberlites and related magmas, interpreted to be related to the latter stages of the breakup of Rodinia and the opening of the Iapetus Ocean. Whole-rock Mel kimberlites have ⁸⁷Sr/⁸⁶Srinitial (0.7054 to 0.7069), εNdinitial (2.4 to 3.0), and εHfinitial (− 15.4 to -1.1) ratios, with the isotopic characteristics of the least contaminated rocks being similar to those of Eoarchean to Cambrian kimberlites in eastern Canada. The compositions of most of the garnets separated from the Mel kimberlites are consistent with a lherzolitic paragenesis, with a subordinate portion having an eclogitic paragenesis. Ni-thermometry results for the lherzolitic garnets record mantle temperatures of 800 °C to 1325 °C. Extrapolation of these temperatures to the West Central Rae geotherm indicates that the lherzolite garnets were derived from depths between 105 and 185 km, with 86% of all investigated garnet grains having an origin within the diamond stability field.
... Further, the B and S isotopes of Mesozoic and Cenozoic carbonatites (28) and alkaline mafic magmas (29), respectively, indicate incorporation of greater quantities of crustal components in their sources. The widespread emergence of geochemically enriched intraplate magmatism since ~300 Ma (Fig. 3A) is also coincident with the frequency distributions of kimberlites (Fig. 3B) (30) and carbonatites (31) and silica-undersaturated mafic magmas more broadly (32). With the exception of carbonatites, these magmas are generally considered to derive from the convecting mantle (6,16,33), indicating that its compositional modification by deeply subducted material was widespread. ...
... Relative age ranges (RAR, %) = (t max -t min )/t × 100. (B) Carbon isotopes (5) and frequency distribution curve(30) for kimberlites over the past 1000 Ma. neodymium isotopes of kimberlites and intracontinental basalts (gray dots) are also shown for comparison. (C) evolution of mantle potential temperature (purple) (10) and seafloor consumptions (green) (34) since 1000 Ma. the vertical columns denote the time frames of supercontinents(40). the horizontal black bar shows the time of convecting mantle enrichment, considering the required recycling time (presented as dashed lines, >250 to 300 Myr)(36,37). ...
Plate tectonics drives the compositional diversity of Earth’s convecting mantle through subduction of lithosphere. In this context, the role of evolving global geodynamics and plate (re)organization on the spatial and temporal distribution of compositional heterogeneities in the convecting mantle is poorly understood. Here, using the geochemical compositions of intracontinental basalts formed over the past billion years, we show that intracontinental basalts with subchondritic initial neodymium-144/neodymium-143 values become common only after 300 million years, broadly coeval with the global appearance of kimberlites with geochemically enriched isotopic signatures. These step changes in the sources of intraplate magmatism stem from a rapid increase in the supply of deeply subducted lithosphere during the protracted formation of Pangea following the widespread onset of “modern” (cold and deep) subduction in the late Neoproterozoic. We argue that the delay (~300 million years) in the appearance of enriched intraplate magmas reflects the time required for the sinking and (re)incorporation of slabs into the sources of mantle-derived magmas.
... Given the kimberlite volcanism, the similar structure and geometry raises the possibility of melt as an explanation. However, this possibility is very unlikely given the lack of elevated regional geothermal conditions and the fact that kimberlites are typically small-volume melts formed via decompression-induced redox melting, do not require deviations from ambient temperatures (Tappe et al., 2018), and so will have limited long-lived thermal impacts on the lithosphere. This possibility is dismissed here but is explored more in the supplemental materials. ...
... The resistivity model in Fig. 3 reveals that the Candle Lake, FALC, and Pikoo kimberlite clusters all erupted along the margin of the NSC conductor (Fig. 3), suggesting a relationship between them and the subducted lithosphere beneath the north Sask Craton. Within kimberlite ascent models (e.g., Jelsma et al., 2009;Tappe et al., 2018; and references therein), the NSC conductor represents a compositional heterogeneity of the Sask Craton mantle lithosphere (Fig. 6). The well-defined borders of the NSC conductor suggest that this heterogeneity has a sharp boundary, likely reflecting a deep-seated fault or mantle terrane boundary. ...
Long-period magnetotelluric (MT) data were collected at 56 locations over the Sask Craton in 2021 and 2022. The data were combined with existing broadband data and inverted to produce a 3-D resistivity model of the Sask Craton and Trans-Hudson Orogen (THO). The model reveals a number of northeast striking electrically conductive crustal structures that extend into the mantle lithosphere. In the mantle lithosphere, these conductors coalesce into a single large low resistivity anomaly in the depth range 70–85 km termed the Northern Sask Craton (NSC) conductor. The resistivity of the NSC conductor is attributed to sulfides deposited along an interface between a flat slab that was accreted to the base of the pre-THO Sask Craton lithosphere during closure of the Manikewan Ocean. Kimberlites have erupted along the margin of the NSC conductor. The boundary of the conductor likely represents deep-seated faults and mantle terrane boundaries formed during flat slab subduction that allowed the ascent of kimberlite melts. The resistivity of the northeast-trending conductors can be interpreted as due to graphite and sulfides precipitated by past fluid or melt flow during ocean closure and orogensis. A number of these conductors are located beneath known mineral districts and trends and may represent source pathways for regional base and precious metal deposits. Other conductors may represent possible, previously unknown, regions hosting mineralization. Many of these conductors are associated with major regional faults and shear zones, which may be deep-seated features that helped to guide both kimberlites and mineralizing fluids. Of the prominent northeast-trending conductors west of the Sask Craton, one corresponds to the previously reported North American Central Plains (NACP) conductor. The new model shows that this conductor abruptly terminates at 54 °N and is not observed farther south in the model. This shows that the NACP is not as spatially continuous as previously suggested, suggesting that the tectonic processes that formed the THO were not as uniform along-strike as shown in existing tectonic models. The connection of one of the northeast-trending anomalies to the NSC conductor suggests that a previously unrecognized phase of east-dipping subduction may have occurred beneath the Sask Craton as the THO was formed.
... Despite steeper subduction being a characteristic of the Proterozoic, its correlation with the distribution of kimberlite remains uncertain (e.g. Tappe et al. 2018). For example, the oldest known kimberlite is of late Mesoarchean age (2850 Ma) (de Wit et al. 2016). ...
... Recent petrologic and geochemical constraints suggest that the volatile-rich nature of kimberlite melt requires the incipient melting of the upper convecting mantle (Giuliani et al. 2023), a condition achievable in a relatively colder mantle. Tappe et al. (2018) proposed that secular cooling of the mantle has the dominant effect on the kimberlite magmatism and onset of plate tectonics cannot be inferred from the kimberlite distribution alone, although others (e.g. Liu et al. 2023) have acknowledged the importance of both thermo-tectonic changes for the occurrence of kimberlite throughout Earth's history. ...
Temporal changes in Earth's tectonic style play a crucial role in understanding the planet's evolution. Modern-style tectonics is characterized by the formation of basaltic crust at divergent plate boundaries and its subsequent recycling at subduction zones, accompanied by wedge mantle formation and arc magmatism. It is commonly believed that the secular cooling of the mantle modified the tectonic style from stagnant lid or heat pipe on an early hotter Earth to horizontal tectonics during Meso-Neoarchean. However, various field, petrographic, and geochem-ical studies suggest that the onset of plate tectonics ranges from Hadean to Neoproterozoic. In this study, we re-evaluate the primary magma temperature (mantle potential temperature, T p) of the upper ambient mantle, spanning from Eoarchean to Neoproterozoic. We used basalts from several Archean and Proterozoic greenstone belts worldwide, along with Proterozoic ophiolites, to (re) calculate the T p using the FRACTIONATE-PT method. We observed a T p range of 1444-1639°C during the Archean and 1414-1611°C during the Proterozoic. These findings indicate a strong correlation with previously estimated T p values obtained from PRIMELT3 method. This further highlights strong internal consistency among different methods and supports models of a hot ambient mantle during the Archean and Proterozoic. We further reviewed numerical models regarding the effect of mantle temperature on the viability of early Earth plate tectonics. Such model results, composition of Archean continental crust, recent crustal growth models, and field evidence are consistent with the operation of plate tectonics on an early hotter Earth. The transition from a hotter mantle to a colder one from Eo-Neoarchean resulted in thinner oceanic lithosphere and a less depleted lithospheric mantle. Subduction of this thinner oceanic lithosphere led to modern-style tectonics. The intensity and style of plate tectonics on the early Earth differed from modern tectonics, which emerged during the Neoarchean. ARTICLE HISTORY
... This was done by reconstructing the location of lithosphere presently thicker than 150 km, determining its intersection with either fixed or mobile basal mantle structures, and averaging the results over the last 320 Myr. The results are in general agreement with the locations of kimberlite eruptions in the database of Tappe et al. (2018) both for fixed and moving basal mantle structures (Fig. 1). The strong spatial-statistical relationship between kimberlites and basal mantle structures is somewhat unexpected because LIPs that are the product of deep mantle plumes are not systematically associated with kimberlites (Ernst & Jowitt, 2013). ...
... This work mapped the evolution of broad mantle upwelling in forward reconstructions of past mantle flow (Fig. 2). It showed that broad mantle upwelling primarily occurs above moving basal mantle structures (Fig. 2b-c), and that there is a strong spatial-statistical relationship between the kimberlite eruptions in the database of Tappe et al. (2018) and the predicted broad mantle upwelling. The models show that deep Earth material is transported to the source region of kimberlite melt, which is consistent with the geochemical signature of some kimberlites (Giuliani et al., 2021). ...
... However, the exponential decay signature is not observed in our predictions (Figure 2b). In addition, the increase of kimberlite occurrences has been proposed to be concomitant with the respective rise and fall of Archean komatiite and Proterozoic anorthosite frequency (Mitchell et al., 2022;Tappe et al., 2018). It is noted that zircon saturation in melts generally increases with the decreased SiO 2 content (Shao et al., 2020), indicating low abundances of zircon records for the natural silica-undersaturated carbonatites, kimberlites, and mafic rocks. ...
... The 650 500 Ma age cluster characterizes the widespread carbonatites, anorogenic granitoids, and (nepheline-) syenites produced during the post-collisional phase of the Pan-African orogens associated with the assembly of Gondwana (Veevers, 2007) and the opening of the Iapetus Ocean corresponding to the final breakup of Rodinia (Robert et al., 2021). The age peak of 250 200 Ma either corresponds to the initial continental rifting across Pangea associated with widespread alkaline, kimberlite, and/or carbonatite magmatism (Matton & Jébrak, 2009;Tappe et al., 2018) or is contemporary with the occurrence of post-collisional alkaline-carbonatite magmatism in the Qinling Orogen, China (Goodenough et al., 2021). Moreover, the Cenozoic (50 0 Ma) carbonatites and alkaline igneous rocks are present in the post-collisional settings of the Tethyan-Himalayan and Laramide orogens (Goodenough et al., 2021) and in the southwestern Pacific, which are conjecturally linked to rifting, mantle plumes or subduction of the Pacific slab (Fan & Hooper, 1991;Finn et al., 2005). ...
Plain Language Summary
The potential of volcanic CO2 emissions to modulate atmospheric CO2 levels and affect the environment of our planet has been recognized. Some specific volcanic types, such as continental arc volcanism, have been hypothesized to play a dominant role in driving long‐term climate change. Recently, the efficiency of continental alkaline magmatism in releasing carbon from the deep mantle to the atmosphere and its ability to influence Earth's climate is proposed for certain timescales and supported by empirical data. However, the quantitative estimation of the alkaline magmatic activity over geologic time and its general link to the global climate change remains poorly constrained. Here, we assess the alkaline magmatic variations based on the detrital zircon record and a novel machine‐learning model which could discriminate zircon from carbonatites, kimberlites and other related alkaline silicate rocks. The predictive result shows several peaks at 1,050−850, 650−500, 250−200, and 50−0 Ma, which is considered a minimum estimation due to the preservation bias of the detrital zircon record. Our estimates indicate that continental alkaline magmatism may influence global warming during specific intervals of geologic time such as the early Paleozoic and early Mesozoic.
... Extended author information available on the last page of the article volatile cycles (Yaxley et al. 2017). Therefore, understanding fO 2 in Earth's mantle is crucial for comprehending terrestrial magmatism and volatile cycles (Foley 2011;Tappe et al. 2018). The fO 2 compositions of the subcontinental lithospheric mantle (SCLM) have been shown to vary with depth and time (Woodland and Koch 2003;Creighton et al. 2009Creighton et al. , 2010Yaxley et al. 2017;Tappe et al. 2021;, which has the potential to shift melting regimes over geological timescales (Foley 2011). ...
... Our results provide the first fO 2 estimates for eclogites and peridotitic garnets from southern India entrained by ca. 1.1 Ga old Mesoproterozoic kimberlites that represent one of the earliest global emplacement events of diamond-bearing deep-sourced magmas (Tappe et al. 2018). ...
Despite over 400 occurrences of kimberlites and related rocks in India, mantle-derived xenoliths are known only from a
few occurrences. This paucity of mantle-derived xenoliths in Indian kimberlites has hampered investigations of the subcontinental lithospheric mantle (SCLM). Using a valuable selection of the rare xenolith inventory, we here report Fe3+/ΣFe
measurements for garnets using the electron microprobe (EPMA) fank method, targeting six mantle eclogite xenoliths (KL2
pipe) and fourteen peridotitic garnet xenocrysts (P9 and P10 hypabyssal intrusions) from the Wajrakarur kimberlite feld
(WKF) on the Eastern Dharwar craton (EDC). These data provide some of the frst direct constraints on the oxygen fugacity (fO2) of the lithospheric mantle beneath the Indian subcontinent. The measured Fe3+/ΣFe ratios vary between 0.02 and
0.05 (±0.01) for the eclogite xenoliths and between 0.02 and 0.10 (±0.01) for the peridotitic garnets. Calculated ΔlogfO2
values for the KL2 eclogites show a wide range from FMQ-3.9 to FMQ-0.9 (±0.6), straddling the boundary between the
diamond and carbonate stability felds. In terms of redox compositions, it appears that the KL2 eclogites are able to host
diamond, which is consistent with the diamondiferous nature of this particular WKF locality and the presence of eclogitic
garnet inclusions in diamonds from the nearby TK4 kimberlite body. The peridotitic garnet xenocrysts from the P9 and P10
kimberlite bodies, which were entrained between ~ 125 and 170 km depth, reveal ΔlogfO2 values between FMQ-4.5 and
FMQ-2.6 (±0.9). Garnet xenocrysts with ‘normal’ REE patterns exhibit higher Fe3+/ΣFe ratios compared to garnets with
‘sinusoidal’ REE patterns. Importantly, the Fe3+/ΣFe ratios of garnet xenocrysts with ‘normal’ REE patterns (~125–160 km
depth) correlate with metasomatic Ti–Y–Zr–V enrichment, which suggests metasomatism-driven oxidation of the cratonic
mantle at mid-lithospheric depths. Such melt-related mantle metasomatism was probably diamond-destructive within the
otherwise diamond-fertile lithospheric keel. The observed wide range of ΔlogfO2 values for the Dharwar cratonic mantle
lithosphere allows for stabilization of various metasomatic phases (e.g., amphiboles, micas, carbonates) that may have
formed (or concentrated in) distinctly diferent metasome assemblages within the continental root that underpins Peninsular
India. Changing the relative contributions from such highly diverse volatile-rich metasomes may explain the spatiotemporal
association of kimberlites and various diamond-bearing potassic magma types such as orangeites, ultramafc lamprophyres
and lamproites, a scenario that is infuenced by the redox composition of the Dharwar craton root.
... Juvenile magmatism at ca. 2000 Ma was globally significant, marking a period of significant crust formation, a transition from komatiite-to kimberlite-style melting, and an increase in continental alkali basaltic magmatism due to enhanced subduction and mantle cooling (Liu et al., 2019a, Tappe et al., 2018. Alkaline and carbonatite magmatism was largely restricted to the cratonic components of southern, east and west Africa (ca. ...
... 2000 Ma paleoreconstructions are not presently tightly constrained. A possible genetic connection may also be supported by the consistent age-Nd-Hfisotope signatures of the EGS mafic rocks and the Bushveld kimberlites, which lie on the isotopic evolution trend of kimberlites through the Proterozoic (see also Fig. 8; Tappe et al., 2018, Woodhead et al., 2019, and their whole-rock geochemistry, which suggests that their parent melts were derived from similarly large, homogeneous, deep and isolated (primordial) mantle reservoirs. Fiorentini et al. (2020) argue that the EGS was a favorable location for far-field Bushveld magmatism due to its thin and more juvenile lithosphere, compared with other parts of the Yilgarn and Pilbara cratons. ...
... This study shows that kimberlites, which derive from the convective mantle 24,25,27,45 , share similar He isotope compositions to the mantle xenoliths they entrain (0.05 to 6 Ra 50,51 ). This overlap con rms previous suggestions that noble gases in mantle xenoliths are dominated by input from entraining and/or precursor magmas which in ltrate the lithospheric mantle not long before eruption 51,74 . ...
The genesis of kimberlites – Earth’s deepest-derived melts – remains an unresolved question despite the economic and scientific interest surrounding these diamond-bearing continental magmas. One critical question is whether they tap ancient, deep mantle or the shallow convecting mantle with partial melting triggered by deep-mantle plumes or plate tectonics. To address this question, we report the compositions of He-Ne-Ar isotopes, formidable tracers of the occurrence of primordial material in the mantle, in magmatic fluids trapped in olivine from kimberlites worldwide. We show that two kimberlites have Ne isotopes less nucleogenic than the upper mantle, which unequivocally requires a deep mantle origin. This is corroborated by previous evidence of negative W isotope anomalies and the location of these kimberlites along age-progressive hot-spot tracks. The lack of strong primordial He isotope signatures indicates overprinting by lithospheric and crustal components, which suggests that Ne isotopes are more robust tracers of deep-mantle contributions in intraplate magmas.
... The identification of phlogopite-bearing mantle xenoliths contributes to a better understanding of asthenospherelithosphere interaction involving melt/fluid migration into the mantle wedge. Due to the lack of reaction zones between K-rich alkaline glass veins and peridotite, we conclude that these veins represent an analogue to proto-kimberlite metasomatism (e.g., Giuliani et al., 2014Giuliani et al., , 2016Aulbach et al., 2017;Tappe et al., 2018;Kargin et al., 2019;Gervasoni et al., 2022;Rodrigues et al., 2023;Braga et al., 2024), occurring immediately before, or coeval with, the ascent of the host magma. In addition, Re-Os model ages (T RD and T MA = 1.3-0.9 ...
Here we report the first investigation of spinel-bearing mantle xenoliths from Los Gemelos volcano, Canquel
Plateau, Patagonia. They are highly-depleted Mesoproterozoic (Re–Os model ages of 1.3–0.9 Ga) harzburgites
and clinopyroxene-poor lherzolites characterized by typical indicators of partial melt extraction, such as low
whole-rock Al2O3 and CaO contents (<1.5 wt%), high Mg# of silicate phases (90–95), and Cr-rich spinel (Cr#
0.20–0.42). Depletion of incompatible highly siderophile elements (Re, Ru, Pd) relative to the primitive upper
mantle supports high degrees of melt extraction. The occurrence of phlogopite and K-rich alkaline glass veins
with high- and low-SiO2 compositions is clear evidence of modal metasomatism. The light rare earth element
(LREE) enrichment in clinopyroxene, as well as the whole-rock U-shaped REE pattern, confirms cryptic metasomatism.
This melt-rock interaction is corroborated by major (i.e., Mg# vs. basaltic elements) and trace (i.e.,
La/YbN vs. Sr/Y and Ti/Eu; and Sr vs. Ti/Eu) element contents of pyroxenes. The calculated compositions of
melts in equilibrium with clinopyroxene coexisting with phlogopite suggest interaction with slab-derived materials.
This metasomatism has been generated by a chromatographic fractionation-reaction process, from deep
to shallow mantle domains. The percolation of a high-K hydrous magma probably is associated with the upwelling
of asthenospheric material through a slab-window, which caused partial melting of oceanic crust and
overlying sediments during the Paleocene. The varying intensities of metasomatic imprints recorded by mantle
xenoliths from Los Gemelos provide valuable insights into the interaction of slab-derived materials near the
lithosphere-asthenosphere boundary, at a distance of ~600 km from the Andean volcanic arc.
... The aillikites occur in three major groups: 1 st as part of alkaline ultrabasic carbonatite complexes (Cordeiro et al., 2010;Tappe et al., 2006;2017;Yunshuai et al., 2018;D'Orazio et al., 2007;Natali et al., 2018;Pirajno, 2015;Woolley et al., 2008) or massifs, 2 nd in association with the kimberlites (Tappe et al., 2018), or form independent intrusions (Hutchison,et al., 2019;Upton et al., 2006) and they differ in compositions in mineralogy. The first group is closer to carbonatites and enriched in TRE and REE and apatite (phosphorus) and HFSE. ...
... Carbonatites have a wide temporal span, ranging from the Archean to Recent volcanic eruptions in Tanzania (Dawson et al. 1994;Tappe et al. 2018;Humphreys-Williams and Zahirovic 2021). Of those reported, the oldest carbonatite found is the 3.01 Ga Tupertalik carbonatite from Greenland (Bizzarro et al. 2002), while the youngest carbonatite is from the Oldoinyo Lengai volcano in Tanzania, which was still active until the 1990s (Dawson et al. 1994). ...
Despite of their scarcity, carbonatites are documented from diverse geological settings, including cratons, continental rifts, orogenic belts, and large igneous provinces, ranging in age from Archean to Recent. This study provides a concise overview of the evolution of igneous carbonatites, compiling data on their diverse characteristics and classifying them into mantle-derived and crustal-derived sub-types. Mantle-derived carbonatites, typically associated with alkaline rocks, are enriched in rare earth elements (REE) and display geochemical affinities to the mantle. By contrast, crustal-derived carbonatites usually show much lower REE contents and crustal-affinity geochemical features similar to sedimentary carbonaceous rocks. Our study documents the significant economic potential of carbonatites which can host world-class deposits of REE, rare metals, alkaline earth metals, and non-metallic resources. Typically, the key processes controlling the REE mineralization include the low-degree melting of refertilised mantle, liquid immiscibility, fractional crystallization, and hydrothermal fluids. Thus, carbonatites are of significant economic value due to the rapidly increasing global demand for REE, mainly driven by the ‘green energy transition’.
... Studies of Melt/Fluid Inclusions in Olivine Tappe et al. (2018) ➢ Confined to locations where 'fresh' olivine is preserved. ...
... The Kapamba lamproites were first described in public by Scott Smith et al. (1989), but had been initially classified as kimberlites in the 1970s, mainly because more than half of these pipes contain small quantities of macro-diamonds despite their setting within the Proterozoic Irumide Belt (Pipe-2 has a grade of 5 cpht; Tappe et al., 2018). Recently, much progress has been made in the understanding of the tectonic evolution of south-central Africa and the petrology of lamproites, which requires a revision of the origin of diamondiferous lamproite volcanism in eastern Zambia. ...
... However, to date, melt structure measurements conducted at high P-T applicable to natural magmatic systems are available only for dolomitic and calcitic liquids representative of carbonatitic melts (Kono et al., 2014b;Hudspeth et al., 2018), melilititic liquids (Stagno et al., 2020b) and liquids representative of basalts erupted at mid-ocean ridges (Sakamaki et al., 2013). No measurements have been conducted in situ on transitional liquids, although their presence at mantle conditions has been established through geochemical (Tappe et al., 2017) and experimental evidence (see Fig. 1 and references in Stagno et al., 2020a). ...
Carbonate-silicate melts that originate in Earth's interior are described as transitional melts which possess compositions intermediate between carbonatitic and basaltic end members. The covariation of key oxides between carbonatite and basalt (e.g., 10-35 wt% SiO2 and 40-10 wt% CO2 , respectively) is expected to have a strong effect on liquid properties. However, due to their paucity both in the record of terrestrial rocks and as quenched glasses, their molecular structure has remained poorly explored to date. We investigated the atomic structure of a synthetic carbonate-silicate liquid with chemical composition within the CaO-MgO-Al2O3-SiO2-FeO-Na2O-ClO−-CO2 oxide system having 18.28 wt% SiO2 and 22.54 wt% CO2 using multi-angle energy dispersive X-ray diffraction at pressures (P) and temperatures (T) of 1.4 GPa/1815 °C, 2.6 GPa/1865 °C, 4.3 GPa/ 1990 °C, 4.4 GPa/1950 °C. The results show that the intermediate range ordering of the structure decreases with an increase of both P and T. Based on this study, the carbonate-silicate magmas at upper mantle P-T conditions are expected to increase their viscosities during their ascent through the mantle as a result of increasing intermediate range ordering upon cooling and decompression. Additionally, spectroscopic measurements were carried out on the quenched glasses at ambient pressure using micro-Raman as well as micro-FTIR in reflection and transmission modes in the mid infrared range. High pressure investigation using micro-FTIR was also conducted. The distribution of Qn species obtained by deconvolution of the Raman spectra within the aluminosilicate region confirms the depolymerized nature of the quenched glasses as inferred by the low viscosities of the corresponding liquids; peculiar characteristics of the C vibrations would suggest a distorted environment surrounding the network modifying CO32− anion. No evidence of molecular CO2 was detected. Notably, we find evidence of both dissolved molecular CO and CO linked to a metal cation forming carbonyl complexes in the quenched glasses at P-T-fo2 conditions compatible with a hot Archean upper mantle. This suggests a role for carbonate-silicate magmas as carriers of reduced gaseous C-O-H species towards the early atmosphere along with the mobilization of PGE-elements.
... Kimberlite, one of the deepest known magmatic rocks on Earth, offers valuable glimpses into the deep mantle composition (Woodhead et al., 2019), craton structure (Gardiner et al., 2020), global geodynamic variation (Tappe et al., 2018), and diamond formation (Giuliani et al., 2023). The accurate determination of the emplacement of this special rock is crucial for revealing such information. ...
... Kimberlites are ultrabasic rocks rich in volatiles and MgO whose magmas rise from great depths to the Earth's surface, carrying a set of crustal and/or mantle-derived xenoliths and xenocrystals, such that olivine, garnet, spinel, chromium-diopside, phlogopite, and diamond (Jelsma et al. 2009;Sparks 2013;Tappe et al. 2018;Woodhead et al. 2019). For this reason, in addition to being the primary source of a valuable mineral resource (diamonds), kimberlite studies provide an opportunity to investigate the chemical composition of the Earth mantle (Torsvik et al. 2010;Mitchell 2021). ...
... Indirect evidence for these subduction processes is associated with the eclogitic garnet and clinopyroxene inclusions in diamonds from the APIP region (Carvalho et al., 2022b) Guarino et al., 2013) suggest a similar source in the Brazilian SCLM, which produced two similar (proto)kimberlite melts that are homogeneous over a large span of time and space. This is supported by the model of global kimberlite volcanism proposed by Tappe et al. (2018). A key element of this model is that kimberlite melts are ubiquitous in the LAB region, and that surface kimberlite magma eruption events are largely dependent on suitable tectonic triggers. ...
... Two models are commonly associated with the formation of silicaundersaturated alkaline basalts: (1) low-degree partial melting of metasomatized lithospheric mantle in the presence of phlogopite or amphibole 22 ; and (2) melting of carbonated peridotite or eclogite in the asthenosphere 15,16,[23][24][25] . Melting of amphibole-bearing lithospheric mantle cannot explain the similarity in trace element patterns between high-Nb basalts and kimberlites, which are well known to derive from amphibole-free carbon-bearing asthenosphere 26,27 . Instead, the high CaO, low SiO 2 contents, and high CaO/Al 2 O 3 of the high-Nb basalts (Fig. S6) are consistent with partial melting experiments of carbonated peridotite 15 , as also invoked for kimberlites 25 . ...
Studies of ocean island basalts have identified a Prevalent Mantle (PREMA) component as a fundamental feature of mantle geochemical arrays; however, its origin and distribution are highly controversial, including its potential link to plumes sourced in low-shear-wave velocity provinces (LLSVPs) above the core-mantle boundary. In this study, we interrogate the compositional systematics of ~ 3500 Cenozoic oceanic and continental sodic basalts to provide insights into the origin and distribution of PREMA. We find that low-degree basaltic melts with high Nb concentrations located away from deep-mantle plumes have PREMA-like Sr-Nd-Hf isotopic signatures, implying that PREMA is highly fusible and not exclusively associated with LLSVPs. Geochemical modelling and mantle convection simulations indicate that PREMA could have been generated soon after Earth accretion, experiencing only minimal melting or enrichment, and then scattered throughout the upper mantle, rather than being the result of mixing between depleted and enriched mantle components.
... Изучение клинопироксена из раннедокембрийских кимберлитов может пролить свет как на проблему состава древней литосферной мантии, так и на изменения во времени протокимберлитового расплава и его источника. Например, в настоящее время остается дискуссионным вопрос о том, эволюционировал ли в ходе геодинамического развития Земли источник первичных кимберлитовых расплавов, или их состав остается постоянным (Tappe et al., 2018;Woodhead et al., 2019). ...
В сборнике статей собраны материалы докладов участников международной научной конференции «Щелочной и кимберлитовый магматизм земли и связанные с ним месторождения стратегических металлов и алмазов», которая прошла в Геологическом институте Кольского научного центра Российской академии наук (г. Апатиты) с 11 по 15 сентября 2023 г. Конференция была организована Геологическим институтом КНЦ РАН, ФИЦ КНЦ РАН и ГЕОХИ РАН. Финансовую поддержку в проведении конференции оказал Кировский филиал АО «Апатит». Конференция посвящена современным проблемам геохимии, петрологии, минералогии и рудного потенциала щелочных пород, карбонатитов и кимберлитов. Отдельное внимание уделено вопросам происхождения и эволюции щелочных магм, минералогии связанных с ними массивов, а также материалам по месторождениям стратегических металлов и алмазов. В пленарных докладах были представлены современные данные о щелочном магматизме Земли и его рудоносности, частичном плавлении перидотитов нижней части литосферы и их связи с процессами формирования кимберлитов, а также о минералого-геохимических особенностях щелочных массивов Северной Танзании и Кольского региона. Об актуальности обсуждаемых на конференции вопросов свидетельствует высокий к ней интерес и география участников. В работе конференции приняли участие исследователи из Геологического института КНЦ РАН (г. Апатиты), Университета им. Бен-Гуриона (г. Беэр-Шева, Израиль), ДВГИ ДВО РАН (г. Владивосток), Воронежского государственного университета (г. Воронеж), Института геохимии им. А.П. Виноградова СО РАН (г. Иркутск), Института геохимии и аналитической химии им. В.И. Вернадского РАН (г. Москва), Геологического института РАН (г. Москва), МГУ им. М.В. Ломоносова (г. Москва), Института геологии рудных месторождений, петрографии, минералогии и геохимии РАН (ИГЕМ РАН, г. Москва), Минералогического музея им. А.Е. Ферсмана РАН (г. Москва), Института геологии и минералогии им. В.С. Соболева СО РАН (г. Новосибирск), Новосибирского национального исследовательского государственного университета (г. Новосибирск), ВНИИОкеангеология им. И.С. Грамберга (г. Санкт-Петербург), ВСЕГЕИ (г. Санкт-Петербург), Института геологии и геохронологии докембрия РАН (г. Санкт-Петербург), Регионального музея Северного Приладожья (г. Сортавала), Института геологии им. Н.П. Юшкина КомиНЦ УО РАН (г. Сыктывкар), ТГУ (г. Томск), Института экспериментальной минералогии им. Д.С. Коржинского РАН (Черноголови), Западно-Якутского научного центра государственного бюджетного учреждения «Академии наук Республики Саха (Якутия)» (ЗЯНЦ АН РС (Я), г. Якутск). С онлайн докладами в конференции приняли участие специалисты из Азербайджана, Ирландии и Израиля. В программу сессии вошло 4 пленарных, 47 устных и 43 стендовых докладов. Во время конференции были проведены полевые однодневные экскурсии на Хибинский массив (устье и отвалы штольни экспериментального рудника на горе Куэльпорр – главная фоидолитовая дуга массива), Ловозёрский массив (вершина и западный склон горы Аллуайв – эвдиалитовый, пойкилитовый и дифференцированный комплексы массива), Хабозёрскую группу интрузий (массивы Африканда, Озёрная и Лесная Вараки).
... Consequently, 133 each cluster of kimberlite pipes carries a distinctive suite of mantle xenoliths that is not necessarily 134 representative of the composition of the lithospheric mantle column under investigation. Our study 135 is bolstered by a statistically significant number of garnet grains (>12,500) recovered from >200 kimberlite pipes from 18 (out of the 21 known) kimberlite fields of the Yakutian Kimberlite Province(Table 1), which is among the largest of its kind on a worldwide basis(Sun et al., 2014;Tappe et al., 2018).An important initial step is to discriminate between mantle-derived garnet xenocrysts and 140 'metamorphic' crust-derived garnet grains. Compositions of metamorphic crustal garnets range 141 from Alm 45-65 Prp 15-45 Grs 10-20 to Alm 70-77 Prp 14-27 Grs 2-9 Sps 1-2(Culí et al., 2021). ...
Many cratonic continental fragments dispersed during the rifting and break-up of Gondwana are bound by steep topographic landforms known as ‘great escarpments’1–4, which rim elevated plateaus in the craton interior5,6. In terms of formation, escarpments and plateaus are traditionally considered distinct owing to their spatial separation, occasionally spanning more than a thousand kilometres. Here we integrate geological observations, statistical analysis, geodynamic simulations and landscape-evolution models to develop a physical model that mechanistically links both phenomena to continental rifting. Escarpments primarily initiate at rift-border faults and slowly retreat at about 1 km Myr⁻¹ through headward erosion. Simultaneously, rifting generates convective instabilities in the mantle7–10 that migrate cratonward at a faster rate of about 15–20 km Myr⁻¹ along the lithospheric root, progressively removing cratonic keels¹¹, driving isostatic uplift of craton interiors and forming a stable, elevated plateau. This process forces a synchronized wave of denudation, documented in thermochronology studies, which persists for tens of millions of years and migrates across the craton at a comparable or slower pace. We interpret the observed sequence of rifting, escarpment formation and exhumation of craton interiors as an evolving record of geodynamic mantle processes tied to continental break-up, upending the prevailing notion of cratons as geologically stable terrains.
Kimberlites represent the primary host of diamonds and the deepest mantle-derived melts at Earth’s surface, making these rocks unique probes of the convective mantle. The complex nature of these rocks and limited access to large sample collections have previously limited knowledge of kimberlite genesis. In this chapter, we provide an in-depth review of the major and trace-element geochemistry of kimberlites including available radiogenic and stable isotope data. These results are compared with those existing for petrologically similar lamproites and ultramafic lamprophyres to address the origin and evolution of kimberlites and discuss their bearing on mantle evolution models.
This study examines the mineral and whole-rock compositions and paleomagnetic dating of lamprophyres from the West Coast Alkaline Complex (WCAC) within the Deccan Large Igneous Province. We aim to elucidate their connection with the Réunion plume, Deccan tholeiite magmatism, the onset of rifting and separation of Seychelles, and the role of lithospheric thinning.
WCAC lamprophyres contain olivine and phlogopite phenocrysts/macrocrysts set in a groundmass of carbonate, clinopyroxene, nepheline, spinel, and melilite. They are characterized by Ti-Al phlogopite and Al-enriched spinels with high Fe2+/(Fe+Mg) ratios. They are undersaturated in silica and rich in MgO, TiO2, and LREEs, resembling the global ultramafic lamprophyres (UMLs).
They originated from an enriched garnet lherzolite mantle, metasomatized by silicate and carbonate veins. Trace-element modeling suggests the derivation of melt by ∼1% partial melting of phlogopite-bearing garnet lherzolite mantle, corresponding to moderate pressure depths (3-4 GPa) and lithospheric mantle thickness of 90-100 km. Palaeomagnetic investigations corroborate their intrusions, primarily during chron C29n, approximately at 65 Ma, which coincided with amplified plate velocities in the Indian Ocean.
Seismic tomography indicates a current lithospheric thickness of about 50 km under the western Indian margin, suggesting a lithospheric delamination of about 40-50 km following the intrusion of lamprophyres at ca. 65 Ma. The initiation of passive rifts in the region, culminating in the separation of the Indian subcontinent and the Seychelles, prompted the UML magmatism. Lithospheric thinning continues along with continental rifting in response to greater plate-tectonic stresses within regions of persistent lithospheric weakness.
Volcanoes and volcanic rocks are hosts to economically very significant quantities of natural resources. Initially, we provide a brief overview of volcanic-hosted ore deposits and their typology. We then focus predominantly on the geology of the principal ore deposit types that characterise volcanic successions and some high-level subvolcanic intrusive settings. These are divided into epithermal precious metal, iron oxide copper–gold (IOCG), volcanic-hosted uranium, komatiitic-hosted nickel sulphide, kimberlitic-hosted diamonds, and volcanic-hosted massive sulphide (VMS) deposits. Epithermal gold deposits represent, in terms of exploration expenditure, the most important type of volcanic-hosted resource thus warranting the greatest attention. We discuss these in terms of today’s active geothermal systems that occupy the same volcano-tectonic environments as the fossil hydrothermal systems which host them and further assess these in more detail by dividing them by volcanic landform or feature and facies associations. IOCG deposits are a relatively new family of hydrothermal ore deposit types, only some of which have a clear spatial and genetic relationship to subvolcanic and volcanic processes and rocks. Most volcanic-hosted uranium deposits are relatively small and low grade; however, some larger and higher-grade resources are known. Both komatiite lavas and komatiite intrusions in Archean (and some Proterozoic) greenstone terrains locally host significant orthomagmatic nickel sulphide (Ni, Cu, PGE) deposits and are one of the world’s major sources of Ni production. Kimberlites and lamproites transport diamond xenocrysts in their “mantle cargo” to the Earth’s surface, where they erupt explosively to form pipe-like bodies representing the remains of volcanoes and their vent systems. Polymetallic VMS deposits represent a distinctive, although highly variable, submarine magmatic–hydrothermal ore deposit type having direct genetic links to both a submarine environment and volcanism, including subvolcanic intrusions. Consideration is also given to volcanic rock reservoirs in hydrocarbon exploration which, with significant exploration successes over the past fifteen years, represent a new frontier field of petroleum exploration globally. Finally, we discuss geothermal energy, which is likely to become a more significant energy resource in the future.
Textural, mineralogical and mineral compositional observations in a suite of Neoproterozoic aillikite and calcite kimberlite dykes from southern West Greenland point to consistent variations in melt major element compositions amongst these silica-undersaturated magma types. The aillikites have notably higher bulk SiO2/CO2, H2O/CO2 and K2O compared to calcite kimberlite. Bulk rock arrays, together with field and petrographic observations, emphasize that flow sorting of olivine and other crystalline phases during magma emplacement is important in controlling the compositions of individual samples from these ultramafic dykes. Flow sorting together with variable overall proportions of entrained lithospheric mantle material result in scatter on element–element plots, which makes the interpretation of regional scale major and trace element geochemical datasets difficult. We argue that a significant proportion of the regional Ni—MgO variation in the ultramafic dyke suite of SW Greenland is due to variation in the proportion of an entrained refractory lithospheric mantle component. Therefore, ratios of elements to MgO can be used as proxies for melt compositions. Ratios of SiO2, TiO2, Al2O3, FeO and K2O over MgO are systematically higher, and CO2/MgO lower, in aillikites compared to calcite kimberlites. The trace element patterns of the calcite kimberlite and aillikite dykes show strong similarities in incompatible element concentrations, resulting in overlapping ratios for the highly to moderately incompatible elements. However, differences in Zr-Hf concentrations between rock types imply differences in mantle source mineralogy. Guided by our observations, we present mixing models that demonstrate that partial flux-melting of phlogopite–ilmenite metasomes within the cratonic mantle lithosphere is capable to produce the geochemical characteristics of aillikites and mela-aillikites in West Greenland. Fusion of cratonic metasomes was initiated by infiltrating asthenosphere-derived carbonatitic melts previously identified as the parental liquids to calcite kimberlite.
The thick late syn‐ to early post‐rift shallow water evaporites in the most distal part of wide rifted margins is paradoxical with the deep depression at crustal breakup time predicted by isostatically compensated lithospheric thinning. Elevation of the distal margin and water depth during deposition of the late syn‐rift evaporites in the central South Atlantic are not well constrained and remain to be quantified. We use forward 2‐D thermo‐mechanical modeling coupled with melt prediction and surface processes to assess the contribution of lithospheric and mantle processes on the distal margin topography and subsidence history during continental rifting. Models show that (a) counter‐flow of depleted lower lithospheric mantle during rifting explains the magma‐poor nature of these margins and (b) weak crust and syn‐rift sediment control the wide crustal necking and subsidence history of the distal margin. Integration of our modeling results with quantified geophysical and geological observations suggests that (a) base level was down to −600 m below present‐day global sea level (bsl) during distal margin formation in the Aptian before sag and evaporite deposition, (b) base level was about −300/−400 m bsl at the end of evaporite deposition, and (c) scenarios with a fixed shallow base level (−400 m bsl) or with an increasing base level from an initially deep position (−1,600 m bsl) during evaporite deposition can both fit the observed evaporite distribution. However, erosional features along the base of evaporites suggest a deep initial base level.
Subducted slabs have been detected in the lower mantle for almost 30 years, yet the presence of foundered cratonic segments in the lower mantle is still unclear and inadequately investigated. We present the first P-wave radial anisotropy tomography of southern Africa (our model SA-RAnis2024), which reveals a contrasting feature of preserved northwest and modified southeast Kalahari cratonic root. Segments from the modified cratonic lithosphere are inferred to have dropped into the shallow lower mantle where seismic evidence of isolated high-velocity anomalies are observed. We detect such a high-velocity anomaly under the southwest margin of the Kalahari craton, which possibly detached from the southeast Zimbabwe craton at ca. 60 Ma based on plate reconstructions. Foundered segments can be partially brought back up to shallow depths, and contribute to the geochemical heterogeneity of younger lithosphere, through large-scale mantle convection.
Continental cratons are characterized by thick lithospheric roots that remain intact for billions of years. However, some cratonic roots appear to have been thinned or completely removed, with the reasons for such thinning being debated. In this study, we obtain a high-resolution full-waveform seismic tomographic model for North America which newly illuminates ongoing craton-thinning. Extensive drip-like transport of lithosphere is imaged from the base of the craton beneath the central United States to the mantle transition zone. Geodynamical modeling suggests that such dripping may be mobilized by the sinking of the deep Farallon slab, whose associated mantle flow can drag material at the base of the craton from afar to the dripping location. There, lithospheric material can descend within the ambient downward mantle flow, even though the slab is presently in the lower mantle. Dripping lithosphere could be further facilitated by prior lithospheric weakening such as due to volatiles released from the slab. Our findings show how cratonic lithosphere can be altered by external forces, and that subduction can play a key role in craton mobilization and thinning even when slabs are at great depths in the mantle.
The paper presents data on the contents of major and trace elements in garnet xenocrysts from kimberlites of the highly dia-mondiferous V. Grib pipe (1100 grains) and weakly diamondiferous TsNIGRI-Arkhangelskaya pipe (446 grains). We have established that the high diamond potential of the V. Grib kimberlite pipe is due to several factors related to the composition and structure of the lithospheric mantle represented by kimberlite: (1) a "cold" regime, with a heat flow of 36-38 mW/m 2 ; (2) a thick "diamond window" (70-102 km), with the depth level of the lower boundary of the lithospheric mantle estimated at >200 km; (3) the high degree of preservation of diamond-bearing peridotites under the P-T conditions of diamond stability despite the high degree of impregnation of the lithospheric-mantle rocks by high-temperature silicate melts. The low diamond content of the TsNIGRI-Arkhangelskaya kimberlite pipe as compared with the V. Grib pipe is due to the following factors: (1) a more intense heat flow in the lithospheric mantle, 38-42 mW/m 2 ; (2) a thinner "diamond window", 10-60 km, with the depth level of the lower boundary of the lithospheric mantle estimated at <200 km; (3) weak impregnation of the rocks of the middle and lower lithospheric mantle by CHO fluid/melt, which might have induced diamond formation; (4) minimum preservation of diamond-bearing peridotites in the lower lithospheric mantle, partly because of the possible impregnation of this zone by high-temperature silicate melts.
Sheared peridotite xenoliths are snapshots of deformation processes that occur in the cratonic mantle shortly before their entrainment by kimberlites. The process of deformation that caused the shearing has, however, been highly debated since the 1970s and remains uncertain. To investigate the processes involved in the deformation, we have studied twelve sheared peridotites from Late Cretaceous (90 Ma) kimberlites in northern Lesotho, on the southeast margin of the Kaapvaal craton. Various deformation textures are represented, ranging from porphyroclastic to fluidal mosaic. Our sample suite consists of eleven garnet peridotites, with various amounts of clinopyroxene, and one garnet-free spinel peridotite with a small amount of clinopyroxene. All of the peridotites are depleted in Fe, and the Mg# of olivine and orthopyroxene range from 91 – 94. Three groups of sheared peridotites are present and have been identified primarily on the basis of Ca contents of olivine and orthopyroxene. The porphyroclasts preserve pre-deformation P-T conditions of 3.5 – 4.5 GPa and 900 – 1100°C (Group I), 5 – 5.5 GPa and 1200 – 1250°C (Group II) and 6±0.5 GPa and 1400±50°C (Group III). Group III samples lie above the 40mW/m² conductive geothermal gradient, indicating thermal perturbation prior to deformation.
The sheared peridotites from Lesotho were affected by various metasomatic events. Pre-deformation metasomatism, involving melts and fluids, is recorded in the porphyroclasts. In Group II and III samples the clinopyroxene porphyroclasts have similar compositions to Cr-rich and Cr-poor clinopyroxene megacrysts, respectively, that have previously described from southern African kimberlites. This suggests a relationship between them. Younger pre-deformation metasomatism is preserved in a zoned garnet from Group II (enrichment in Ti, Zr, Y+HREE) and orthopyroxene in a Group I sample. The latter exhibits a complex zonation, with a highly-enriched (Fe, Ti) inner rim and a less-enriched outer rim. These enrichments must have occurred shortly before deformation. Metasomatism during deformation is revealed by the complex chemical changes recorded in olivine neoblasts with, depending on the sample, increasing or decreasing contents of Ti, Ca, Al, Cr, Mn and Na. Crystallographic preferred orientations of olivine neoblasts are consistent with bimodal, B, C, E, AG-type fabrics and indicate the presence of a hydrous metasomatic agent.
We suggest that, akin to the shallower sheared peridotites (Group I), Group II and III were influenced by early (proto-)kimberlite melt pulses and propose the following model: (Proto-)kimberlitic melts invaded the lower lithosphere. These melts followed narrow shear zone networks, produced by deformation at the lithosphere-asthenosphere-boundary, heated and metasomatized the surrounding peridotites and were responsible for megacryst crystallization. Sheared peridotites from close to the melt conduits (Group III) have compositions comparable to Cr-poor megacrysts, while those located at a greater distance (Group II) resemble Cr-rich megacrysts. Reactive infiltration of volatile-rich proto-kimberlite melts caused rheologically weakening of olivine in the lithospheric mantle. The consequence of this positive feedback mechanism of metasomatism, weakening and deformation -- due to the high magmatic and metasomatic activity in the Late Cretaceous -- is the progressive perforation of the lower Kaapvaal lithosphere by rheologically weak zones and the destruction of the protecting dry and depleted layer at its base. This could have caused the observed thinning and destabilization of the lower lithosphere below the southern margin of the Kaapvaal craton.
Kimberlites are volcanic rocks enriched in CO2 and H2O and derive from the deepest-sourced melts (up to 300 km) that reach Earth’s surface. The mantle processes that generate such deep melts and allow them to traverse through thick (≥150 km), cold lithosphere carrying dense mantle fragments, such as xenoliths and diamonds, are debated. In this Review, we explore the composition, formation and evolution of kimberlite melts and the mechanisms of their ascent. Both deep-mantle plumes and shallower convective motions linked to lithospheric extension could trigger kimberlite melting by bringing upwelling mantle rocks to depths above Fe-metal stability (~160–250 km depth). Despite the CO2 enrichment in kimberlite melts, their sources are peridotites not necessarily enriched in carbon. Kimberlite primary melts are transitional between silicate and carbonate compositions and evolve towards increasing silica and lower CO2 concentrations during ascent, while concurrently interacting with the lithospheric mantle. These ascent processes promote the exsolution of CO2–H2O fluids during decompression, a prerequisite for the fast ascent (up to tens of metres per second) of kimberlite magmas. Key unresolved questions include the volatile and alkali budget of kimberlites and their mantle sources; their relationship with ‘superdeep’ diamonds; and their potential link to plumes from the core–mantle boundary.
Ancient orogens within the supercontinent like Columbia can remain stable evolution as long as the cratons. What kind of lithospheric mantle was beneath those orogens and how it evolved into a stable state are still enigmatic. The Trans‐North China orogen (TNCO) is one of the typical collisional orogens within the Columbia supercontinent and was formed at ca. 1.85 Ga. Our work reveals that a cluster of kimberlites intruded the orogenic belt at ca. 1.54 Ga. These rocks were originally generated under a thick lithosphere (>200 km). Their entrained olivine cores show a composition of overlapping olivines from refractory mantle peridotites. The results suggest a thick and refractory lithospheric mantle beneath the TNCO at ca. 1.54 Ga. Such craton‐like property may result from large volume melt extraction from the lithospheric mantle, possibly caused by the ca. 1.78 Ga large igneous event, which eventually induces the long‐term stability of the TNCO during the subsequent supercontinent cycle.
The continental lithosphere is a vast store for carbon. The carbon has been added and reactivated by episodic freezing and remelting throughout geological history. Carbon remobilization can lead to significant variations in CO2 outgassing and release in the form of magmas from the continental lithosphere over geological timescales. Here we use calculations of continental lithospheric carbon storage, enrichment and remobilization to demonstrate that the role for continental lithosphere and rifts in Earth’s deep carbon budget has been severely underestimated. We estimate that cratonic lithosphere, which formed 2 to 3 billion years ago, originally contained about 0.25 Mt C km–3. A further 14 to 28 Mt C km–3 is added over time from the convecting mantle and about 43 Mt C km–3 is added by plume activity. Re-melting focuses carbon beneath rifts, creating zones with about
150 to 240 Mt C km–3, explaining the well-known association of carbonate-rich magmatic rocks with rifts. Reactivation of these zones can release 28 to 34 Mt of carbon per year for the 40 million year lifetime of a continental rift. During past episodes of supercontinent breakup, the greater abundance of continental rifts could have led to short-term carbon release of at least 142 to 170 Mt of carbon per year, and may have contributed to the high atmospheric CO2 at several times in Earth's history.
Thirty new high precision U-Pb perovskite and zircon ages from kimberlites in central North America delineate a corridor of mid-Cretaceous (115 to 92 Ma) magmatism that extends ∼4000 km from Somerset Island in Arctic Canada through central Saskatchewan to Kansas, U.S.A. The least contaminated whole rock Sr, Nd and Hf isotopic data, coupled with Sr isotopic data from groundmass perovskite indicates an exceptionally limited range in Sr-Nd-Hf isotopic compositions, clustering at the low εNd end of the OIB array. These isotopic compositions are distinct from other studied North American kimberlites and point to a sub-lithospheric source region. This mid-Cretaceous kimberlite magmatism cannot be related to mantle plumes associated with the African or Pacific large low-shearwave velocity province (LLSVP). All three kimberlite fields are adjacent to strongly attenuated lithosphere at the edge of the North American craton. This facilitated edge-driven convection, a top-down driven processes that caused decompression melting of the transition zone or overlying asthenosphere. The inversion of ringwoodite and/or wadsleyite and release of H2O, with subsequent metasomatism and synchronous wet partial melting generates a hot CO2- and H2O-rich proto-kimberlite melt. Emplacement in the crust is controlled by local lithospheric factors; all three kimberlite fields have mid-Cretaceous age, re-activated major deep-seated structures that facilitated kimberlite melt transit through the lithosphere.
We present the first oxygen fugacity (fO2) profile through the cratonic lithospheric mantle under the Panda kimberlite (Ekati Diamond Mine) in the Lac de Gras kimberlite field, central Slave Craton, northern Canada. Combining this data with new and existing data from garnet peridotite xenoliths from an almost coeval kimberlite (A154-N) at the nearby Diavik Diamond Mine demonstrates that the oxygen fugacity of the Slave cratonic mantle varies by several orders of magnitude as a function of depth and over short lateral distances. The lower part of the diamond-bearing Slave lithosphere (>120–130 km deep) has been oxidized by up to 4 log units in fO2, and this is clearly linked to metasomatic enrichment. Such coupled enrichment and oxidation was likely caused by infiltrating carbonate-bearing, hydrous, silicate melts in the presence of diamond, a process proposed to be critical for “pre-conditioning” deep lithospheric mantle and rendering it suitable for later generation of kimberlites and other SiO2-undersaturated magmas.
Chemical composition of mafic magmas is a critical indicator of physico-chemical conditions, such as pressure, temperature and fluid availability, accompanying melt production in the mantle and its evolution in the continental or oceanic lithosphere. Recovering this information has fundamental implications in constraining the thermal state of the mantle and the physics of mantle convection throughout the Earth's history. Here, a statistical approach is applied to a geochemical database of about 22,000 samples from the mafic magma record. Potential temperatures (Tps) of the mantle derived from this database, assuming melting by adiabatic decompression and a Ti-dependent (Fe2O3/TiO2=0.5) or constant redox condition (Fe2+/∑Fe = 0.9 or 0.8) in the magmatic source, are thought to be representative of different thermal “horizons” (or thermal heterogeneities) in the ambient mantle, ranging in depth from a shallow sublithospheric mantle (Tp minima) to a lower thermal boundary layer (Tp maxima). The difference of temperature (Δ Tp) observed between Tp maxima and minima did not change significantly with time (∼170°C). Conversely, a progressive but limited cooling of ∼150°C is proposed since ∼2.5 Gyr for the Earth's ambient mantle, which falls in the lower limit proposed by Herzberg et al [2010] (∼ 150 to 250°C hotter than today). Cooling of the ambient mantle after 2.5 Ga is preceded by a high-temperature plateau evolution and a transition from dominant plumes to a plate tectonics geodynamic regime, suggesting that subductions stabilized temperatures in the Archaean mantle that was in warming mode at that time.
We want to know when plate tectonics began and will consider any important Earth feature that shows significant temporal evolution. Kimberlites, the primary source of diamonds, are rare igneous features. We analyze their distribution throughout Earth history; most are young (similar to 95% are younger than 0.75 Ga), but rare examples are found as far back as the Archean (older than 2.5 Ga). Although there are differing explanations for this age asymmetry (lack of preservation, lack of exposure, fewer mantle plumes, or lack of old thick lithosphere in the Archean and Proterozoic), we suggest that kimberlite eruptions are a consequence of modernstyle plate tectonics, in particular subduction of hydrated oceanic crust and sediments deep into the mantle. This recycling since the onset of modern-style plate tectonics ca. 1 Ga has massively increased mantle CO2 and H2O contents, leading to the rapid and explosive ascent of diamond-bearing kimberlite magmas. The age distribution of kimberlites, combined with other large-scale tectonic indicators that are prevalent only in the past similar to 1 Ga (blueschists, glaucophane-bearing eclogites; coesite-or diamond-bearing ultrahigh-pressure metamorphic rocks; lawsonite-bearing metamorphic rocks; and jadeitites), indicates that plate tectonics, as observed today, has only operated for <25% of Earth history.
From the discovery of diamonds in South Africa in 1866 until the end of 2013, Africa is estimated to have produced almost 3.2 Bct out of a total global production of 5.03 Bct, or 63.6% of all diamonds that have ever been mined. In 2013 African countries ranked 2nd (Botswana), 3rd (DRC), 6th (Zimbabwe), 7th (Angola), 8th (South Africa), and 9th (Namibia), in terms of carat production and 1st (Botswana), 4th (Namibia), 5th (Angola), 6th (South Africa), 7th (Zimbabwe), and 9th (DRC), in terms of value of the diamonds produced. In 2013 Africa produced 70.6 Mct out of a global total of 130.5 Mct or 54.1%, which was valued at US 14.1 billion.
Megacrystic (>1 cm) clinopyroxene (Cr-diopside) and garnet (Cr-pyrope) xenocrysts within kimberlites from Lac de Gras (Northwest Territories, Canada) contain fully crystallized melt inclusions. These ‘polymineralic inclusions’ have previously been interpreted to form by necking down of melts at mantle depths. We present a detailed petrographical and geochemical investigation of polymineralic inclusions and their host crystals to better understand how they form and what they reveal about the evolution of kimberlite melt. Genetically, the megacrysts are mantle xenocrysts with peridotitic chemical signatures indicating an origin within the lithospheric mantle (for the Cr-diopsides studied here ~4.6 GPa, 1015 °C). Textural evidence for disequilibrium between the host crystals and their polymineralic inclusions (spongy rims in Cr-diopside, kelyphite in Cr-pyrope) is consistent with measured Sr isotopic disequilibrium. The preservation of disequilibrium establishes a temporal link to kimberlite eruption. In Cr-diopsides, polymineralic inclusions contain phlogopite, olivine, chromite, serpentine, and calcite. Abundant fluid inclusion trails surround the inclusions. In Cr-pyropes, the inclusions additionally contain Al-spinel, clinopyroxene, and dolomite. The major and trace element compositions of the inclusion phases are generally consistent with the early stages of kimberlite differentiation trends. Extensive chemical exchange between the host phases and the inclusions is indicated by enrichment of the inclusions in major components of the host crystals, such as Cr2O3 and Al2O3. This chemical evidence, along with phase equilibria constraints, supports the proposal that the inclusions within Cr-diopside record the decarbonation reaction: dolomitic melt + diopside → forsterite + calcite + CO2, yielding the observed inclusion mineralogy and producing associated (CO2-rich) fluid inclusions. Our study of polymineralic inclusions in megacrysts provides clear mineralogical and chemical evidence for an origin of kimberlite that involves the reaction of high-pressure dolomitic melt with diopside-bearing mantle assemblages producing a lower-pressure melt that crystallizes a calcite-dominated assemblage in the crust.
Archaean komatiites (ultramafic lavas) result from melting under extreme conditions of the Earth's mantle. Their chemical compositions evoke very high eruption temperatures, up to 1,600 degrees Celsius, which suggests even higher temperatures in their mantle source. This message is clouded, however, by uncertainty about the water content in komatiite magmas. One school of thought holds that komatiites were essentially dry and originated in mantle plumes while another argues that these magmas contained several per cent water, which drastically reduced their eruption temperature and links them to subduction processes. Here we report measurements of the content of water and other volatile components, and of major and trace elements in melt inclusions in exceptionally magnesian olivine (up to 94.5 mole per cent forsterite). This information provides direct estimates of the composition and crystallization temperature of the parental melts of Archaean komatiites. We show that the parental melt for 2.7-billion-year-old komatiites from the Abitibi greenstone belt in Canada contained 30 per cent magnesium oxide and 0.6 per cent water by weight, and was depleted in highly incompatible elements. This melt began to crystallize at around 1,530 degrees Celsius at shallow depth and under reducing conditions, and it evolved via fractional crystallization of olivine, accompanied by minor crustal assimilation. As its major- and trace-element composition and low oxygen fugacities are inconsistent with a subduction setting, we propose that its high H2O/Ce ratio (over 6,000) resulted from entrainment into the komatiite source of hydrous material from the mantle transition zone. These results confirm a plume origin for komatiites and high Archaean mantle temperatures, and evoke a hydrous reservoir in the deep mantle early in Earth's history.
Absolute reconstructions of large igneous provinces (LIPs) for the past 300 Ma reveal a remarkable spatial pattern suggesting that almost all LIPs have erupted over the margins of the two large-scale structures in the Earth's lower mantle commonly referred to as the Large Low Shear-wave Velocity Provinces (LLSVPs). This correlation suggests that mantle plumes that have triggered LIP eruptions rose from the margins of LLSVPs, implying long-term stability of these structures and suggesting that they may be chemically distinct from the bulk of the mantle. Yet, some researchers consider the LLSVPs to be purely thermal upwellings, arguing that the observed distribution of LIPs can be explained by plumes randomly forming over the entire areas of LLSVPs. Here we examine the correlation between the LIPs and LLSVPs using nonparametric statistical tests, updated plate reconstructions, and a large number of alternative definitions of LLSVPs based on seismic tomography. We show that probability models assuming plume sources originating at the margins of LLSVPs adequately explain the observed distribution of reconstructed LIPs. In contrast, we find strong evidence against the models seeking to link LIPs with plumes randomly forming over the entire LLSVP areas. However, the hypothesis proposing that the correlation can be explained by plumes randomly forming over a larger area of slower-than-average shear wave velocities in the lowermost mantle cannot be ruled out formally. Our analysis suggests that there is no statistically sound reason for questioning the hypothesis that the LIPs correlate with the margins of LLSVP globally. This article is protected by copyright. All rights reserved.
Plate tectonics plays a vital role in the evolution of our planet. Geochemical analysis of Earth's oldest continental crust suggests that subduction may have begun episodically about 3.8 to 3.2 billion years ago, during the early Archaean or perhaps more than 3.8 billion years ago, during the Hadean. Yet, mantle rocks record evidence for modern-style plate tectonics beginning only in the late Archaean, about 3 billion years ago. Here we analyse the nitrogen abundance, as well as the nitrogen and carbon isotopic signatures of Archaean placer diamonds from the Kaapvaal craton, South Africa, which formed in the upper mantle 3.1 to 3.5 billion years ago. We find that the diamonds have enriched nitrogen contents and isotopic compositions compared with typical mantle values. This nitrogen geochemical fingerprint could have been caused by contamination of the mantle by nitrogen-rich Archaean sediments. Furthermore, the carbon isotopic signature suggests that the diamonds formed by reduction of an oxidized fluid or melt. Assuming that the Archaean mantle was more reduced than the modern mantle, we argue that the oxidized components were introduced to the mantle by crustal recycling at subduction zones. We conclude, on the basis of evidence from mantle-derived diamonds, that modern-style plate tectonics operated as early as 3.5 billion years ago.
The oldest blueschists—metamorphic rocks formed during subduction—are of Neoproterozoic age, and 0.7–0.8 billion years old. Yet, subduction of oceanic crust to mantle depths is thought to have occurred since the Hadean, over 4 billion years ago. Blueschists typically form under cold geothermal gradients of less than 400 °C GPa−1, so their absence in the ancient rock record is typically attributed to hotter pre-Neoproterozoic mantle prohibiting such low-temperature metamorphism; however, modern analogues of Archaean subduction suggest that blueschist-facies metamorphic conditions are attainable at the slab surface. Here we show that the absence of blueschists in the ancient geological record can be attributed to the changing composition of oceanic crust throughout Earth history, which is a consequence of secular cooling of the mantle since the Archaean. Oceanic crust formed on the hot, early Earth would have been rich in magnesium oxide (MgO). We use phase equilibria calculations to show that blueschists do not form in high-MgO rocks under subduction-related geothermal gradients. Instead, the subduction of MgO-rich oceanic crust would have created greenschist-like rocks—metamorphic rocks formed today at low temperatures and pressures. These ancient metamorphic products can hold about 20% more water than younger metamorphosed oceanic crust, implying that the global hydrologic cycle was more efficient in the deep geological past than today.
Experiments are applied to constrain the composition of primary kimberlitic magmas which were in equilibrium with lithospheric peridotite and could resorb the entrained diamond to form typical dissolution features. The experiments are run on samples of a model carbonatite and a melt of the Udachnaya kimberlite at 6.3 GPa and 1400 °C, and at unbuffered or Re–ReO2-buffered oxygen fugacity (1–2 log units above Ni–NiO). Near-liquidus dry Fe3+-free carbonatitic melt (derived from carbonated harzburgite) is saturated with the Ol–Grt–Opx–Mgs assemblage and is almost inert to diamond. Carbonatitic melts that bear 4.6–6.8 wt% Fe2O3 or 1.5 wt% H2O are in equilibrium only with Mgs ± Ol near the liquidus. Dissolution of diamond by these melts produces surface textures uncommon (corrosion sculptures) or common (negative-oriented trigons, shield-shaped laminae and elongate hillocks) to kimberlitic diamonds. The near-liquidus melt of the Udachnaya kimberlite (Yakutia) with 10–12 wt% H2O is saturated with the Ol–Grt–Cpx assemblage and may result from melting of carbonated garnet-bearing wehrlite. Hydrous kimberlitic melt likewise resorbs diamonds forming typical negative-oriented trigons, shield-shaped laminae and elongate hillocks on their surfaces. Therefore, the melts that could originate in the thermal conditions of subcratonic lithosphere, entrain diamond and dissolve it to produce dissolution features on crystal surfaces, were compositionally close to kimberlite (16–19 wt% SiO2) and rich in H2O. Dry Fe3+-bearing carbonatites with fO2 controlled by the ferric/ferrous equilibrium slightly above the Ni–NiO buffer cannot be diamond carriers.
Kimberlite pipes or dykes tend to occur in clusters (a few kilometres in diameter) within fields ∼30–50 km in diameter. They
are generally considered to originate from low degrees of partial melting of carbonated peridotite within zones of ascending
mantle. Numerical modelling shows that at the depth of formation of kimberlite melts (≫200 km), mantle compaction processes
can result in the formation of melt pockets a few tens of kilometres across, with melt concentrations up to 7%. The initiation
of swarms of kimberlite dykes at the top of these melt pockets is inevitable because of the large excess pressure between
the melt and the surrounding solid, which exceeds the hydraulic fracturing limit of the overlying rocks. After their initiation
at mantle depth the swarm of dykes may reach the surface of the Earth when the entire cratonic lithosphere column is in extension.
We propose that kimberlite fields represent the surface envelope of dyke swarms generated inside a melt pocket and that kimberlite
clusters represent the discharge of melt via dykes originating from sub-regions of the pocket. This model reproduces the worldwide
average diameter of kimberlite fields and is consistent with the observation that some of the main kimberlite fields display
age ranges of c. 10 Myr. It is deduced that, at the scale of the Kaapvaal craton, different fields such as Kimberley, N. Lesotho and Orapa,
dated at 80–90 Ma, probably result from synchronous melt pockets forming inside an ascending mantle flow. The same model could
apply to the fields of the Rietfontein, Central Cape and Gibeon districts dated at 60–70 Ma. It is suggested that the same
mantle flow that produced the Kimberley, N. Lesotho and Orapa fields migrated over ∼20–30 Myr a few hundred kilometres westward
to form the Rietfontein, Central Cape and Gibeon fields.
The rate of growth of the continental crust is controversial. We present an evaluation of time-constrained analyses of oxygen isotopes in zircon grains and incompatible element (Zr, Th) concentrations in magmatic rocks to test for variations in the degree of crustal recycling through geological time. The data indicate a rise in these geochemical proxies from ca. 3.0 Ga to a statistically significant peak at 1.2-1.1 Ga during the amalgamation of supercontinent Rodinia, and a decrease thereafter. When combined with other geological and geophysical observations, the data are interpreted as a consequence of an unprecedented level of crustal recycling and sediment subduction during Rodinia assembly, arising from a "Goldilocks" (i.e., just right) combination of larger, thicker plates on a warmer Earth with more rapid continental drift relative to modern Earth. The subsequent decrease in delta O-18, Zr, and Th measurements is interpreted to reflect decreasing drift rates on a cooling Earth.
We report the U–Pb age and Sr/Nd isotope composition for perovskite isolated from forty six kimberlite samples located in the newly discovered Chidliak field on Baffin Island, Canada. The minimum duration of kimberlite magmatism in this field was 17.9 m.y. from 157.0 to 139.1 Ma and represents a new Jurassic kimberlite field in NE Canada. The most prolific period of kimberlite magmatism occurred between 152 and 142 Ma (80% of dated kimberlites). Kimberlitic perovskite from these intrusions display a range in ⁸⁷Sr/⁸⁶Sr (0.7043 to 0.7030) and εNdT values (+3.9 to −0.4), overlapping the isotopic field previously defined for southern African Group I kimberlites.
The ages and isotopic compositions obtained for Chidliak magmatism are identical to a number of Jurassic kimberlite fields in eastern North America and SW Greenland. Some of this Jurassic kimberlite magmatism has a link to one or more mantle plume hotspot tracks but the Chidliak kimberlites have an origin in the deep subcontinental lithospheric mantle and are part of a Jurassic magmatic province that erupted along both margins of Davis Strait; linked to upwelling asthenosphere, continental rifting, and Mesozoic–Cenozoic development of oceanic crust in the Labrador Sea basin. In contrast, the location of other eastern North American Jurassic kimberlites when plotted on a Jurassic continental reconstruction aligns closely to the northernmost projection of contours 2–4 of the African large low shearwave velocity province, consistent with a link to mantle plumes derived from the African mantle plume generating zone.
We report combined U-Pb ages and Sr-Nd isotope compositions of perovskites from 50 kimberlite occurrences, sampled from 9 fields across the Yakutian kimberlite province on the Siberian craton. The new U-Pb ages, together with previously reported geochronological constraints, suggest that kimberlite magmas formed repeatedly during at least 4 episodes: Late Silurian-Early Devonian (419-410 Ma), Late Devonian-Early Carboniferous (376-347 Ma), Late Triassic (231-215 Ma), and Middle/Late Jurassic (171-156 Ma). Recurrent kimberlite melt production beneath the Siberian craton - before and after flood basalt volcanism at 250 Ma - provides a unique opportunity to test existing models for the origin of global kimberlite magmatism.
Groundmass perovskite has been dated by LA-ICPMS in 135 kimberlites and related rocks from 110 localities across southern Africa. Sr and/or Nd isotopes have been analysed by LA-MC-ICPMS in a subset of these and integrated with published data. The age distribution shows peaks at 1,600–1,800, 1,000–1,200, 500–800 and 50–130 Ma. The major “bloom” of Group I kimberlites at ca 90 ± 10 Ma was preceded by a slow build-up in magmatic activity from ca 180 Ma. The main pulse of Group II kimberlites at 120–130 Ma was a distinct episode within this build-up. Comparison of the isotopic data with seismic tomography images suggests that metasomatized subcontinental lithospheric mantle (SCLM) with very low ε
Nd and high 87Sr/86Sr, (the isotopic signature of Group II kimberlites) was focused in low-Vs zones along translithospheric structures. Such metasomatized zones existed as early as 1,800 Ma, but were only sporadically tapped until the magmatic build-up began at ca 180 Ma, and contributed little to the kimberlitic magmas after ca 110 Ma. We suggest that these metasomatized volumes resided in the deep SCLM and that their low-melting point components were “burned off” by rising temperatures, presumably during an asthenospheric upwelling that led to SCLM thinning and a rise in the ambient geotherm between 120 and 90 Ma. The younger Group I kimberlites therefore rarely interacted with such SCLM, but had improved access to shallower volumes of differently metasomatized, ancient SCLM with low 87Sr/86Sr and intermediate ε
Nd (0–5). The kimberlite compositions therefore reflect the evolution of the SCLM of southern Africa, with metasomatic-enrichment events from as early as 1.8 Ga, through a major thermal and compositional change at ca 110 Ma, and the major kimberlite “bloom” around 90 Ma.
The rapid increase of carbon dioxide concentration in Earth's modern atmosphere is a matter of major concern. But for the atmosphere of roughly two-and-half billion years ago, interest centres on a different gas: free oxygen (O2) spawned by early biological production. The initial increase of O2 in the atmosphere, its delayed build-up in the ocean, its increase to near-modern levels in the sea and air two billion years later, and its cause-and-effect relationship with life are among the most compelling stories in Earth's history.
New geochemical data of the crater-facies Tokapal kimberlite system sandwiched between the lower and upper stratigraphic horizons of the Mesoproterozoic Indrāvati Basin are presented. The kimberlite has been subjected to extensive and pervasive low-temperature alteration. Spinel is the only primary phase identifiable, while olivine macrocrysts and juvenile lapilli are largely pseudomorphed (talc-serpentine-carbonate alteration). However, with the exception of the alkalies, major element oxides display systematic fractionation trends; likewise, HFSE patterns are well correlated and allow petrogenetic interpretation. Various crustal contamination indices such as (SiO2 + Al2O3 + Na2O) / (MgO + K2O) and Si/Mg are close to those of uncontaminated kimberlites. Similar La/Yb (79-109) of the Tokapal samples with those from the kimberlites of Wajrakarur (73-145) and Narayanpet (72-156), Eastern Dharwar craton, southern India imply a similarity in their genesis. In discriminant plots involving HFSE the Tokapal samples display strong affinities to Group II kimberlites from southern Africa and Central India as well as to ‘transitional kimberlites’ from the Eastern Dharwar craton, southern India, and those from the Prieska and Kuruman provinces of southern Africa. There is a striking similarity in the depleted-mantle (TDM) Nd model ages of the Tokapal kimberlite system, Bastar craton, the kimberlites from NKF and WKF, Eastern Dharwar craton, and the Majhgawan diatreme, Bundelkhand craton, with the emplacement age of some of the lamproites from within and around the Palaeo-Mesoproterozoic Cuddapah basin, southern India. These similar ages imply a major tectonomagmatic event, possibly related to the break-up of the supercontinent of Columbia, at 1.3 -1.5 Ga across the three cratons. The ‘transitional’ geochemical features displayed by many of the Mesoproterozoic potassic-ultrapotassic rocks, across these Indian cratons are inferred to be memories of the metasomatising fluids/melts imprinted on their source regions during this widespread event.
Kimberlites are a volumetrically minor component of the Earth's volcanic record, but are very important as the major commercial source of diamonds and as the deepest samples of the Earth's mantle. They were predominantly emplaced from ≈2,100 Ma to ≈10 ka ago, into ancient, stable regions of continental crust (cratons), but are also known from continental rifts and mobile belts. Kimberlites have been reported from almost all major cratons on all continents except for Antarctica. Here we report the first bona fide Antarctic kimberlite occurrence, from the northern Prince Charles Mountains, emplaced during the reactivation of the Lambert Graben associated with rifting of India from Australia-Antarctica. The samples are texturally, mineralogically and geochemically typical of Group I kimberlites from more classical localities. Their ≈120 Ma ages overlap with those of many kimberlites from other world-wide localities, extending a vast Cretaceous, Gondwanan kimberlite province, for the first time, into Antarctica.
We defined a new global moving hot spot reference frame (GMHRF), using a
comprehensive set of radiometric dates from arguably the best-studied
hot spot tracks, refined plate circuit reconstructions, a new plate
polygon model, and an iterative approach for estimating hot spot motions
from numerical models of whole mantle convection and advection of plume
conduits in the mantle flow that ensures their consistency with surface
plate motions. Our results show that with the appropriate choice of a
chain of relative motion linking the Pacific plate to the plates of the
Indo-Atlantic hemisphere, the observed geometries and ages of the
Pacific and Indo-Atlantic hot spot tracks were accurately reproduced by
a combination of absolute plate motion and hot spot drift back to the
Late Cretaceous (˜80 Ma). Similarly good fits were observed for
Indo-Atlantic tracks for earlier time (to ˜130 Ma). In contrast,
attempts to define a fixed hot spot frame resulted in unacceptable
misfits for the Late Cretaceous to Paleogene (80-50 Ma), highlighting
the significance of relative motion between the Pacific and
Indo-Atlantic hot spots during this period. A comparison of absolute
reconstructions using the GMHRF and the most recent global paleomagnetic
frame reveals substantial amounts of true polar wander at rates varying
between ˜0.1°/Ma and 1°/Ma. Two intriguing, nearly equal
and antipodal rotations of the Earth relative to its spin axis are
suggested for the 90-60 Ma and 60-40 Ma intervals (˜9° at a
0.3-0.5°/Ma rate); these predictions have yet to be tested by
geodynamic models.
Idealized conceptual models of supercontinent cyclicity must be tested against the geologic record using pre-Pangean reconstructions. We integrate tectonostratigraphic records and paleomagnetic data from Siberia, Laurentia, and Baltica to produce a quantitative reconstruction of the core of the Nuna supercontinent at 1.9-1.3 Ga. In our model, the present southern and eastern margins of Siberia juxtapose directly adjacent to, respectively, the arctic margin of Laurentia and the Uralian margin of Baltica. Consistent tectonostratigraphic records of the three cratons collectively indicate the history of Nuna's assembly and breakup. According to this reconstruction, the late Mesoproterozoic transition from Nuna to Rodinia appears to have been much less dramatic than the subsequent late Neoproterozoic transition from Rodinia to Gondwana.
Partial melting experiments at 40, 50 and 60 kbar pressure on three peridotite compositions with 0.5–0.63 wt.% H2O and 2.0–3.2 wt.% CO2 added indicate melting temperatures only marginally above continental geotherms. Most experiments were performed on a composition with 1.5 wt.% K2O added, which causes a further decrease of about 40 °C in melting temperature. Melts progress gradually from carbonate-rich to carbonated silicate in composition: near-solidus melts have Ca/(Ca + Mg) of 0.46–0.53, which fall to < 0.40 more than 50 °C above the solidus. With increasing temperature for the K-enriched peridotite HPK at 50 kbar, melts are characterised by strong increases in SiO2 (< 3 to > 30 wt.%) and Al2O3 (< 1 to > 9 wt.%) and concomitant decrease in CaO (> 20 to < 3 wt.%), with little change in MgO. K2O and TiO2 exhibit maxima at intermediate temperatures, reflecting the stability of phlogopite and ilmenite above the solidus, indicating the presence of up to 13 wt.% K2O and 2.6 wt.% TiO2 in carbonate-rich melts with only 13 wt.% SiO2. Of 30 trace elements, only Cr, Mn, Ni, and Zn are compatible in the residue, whereas U, Rb, Ba and the LREE are most enriched in the melts. Low melt fractions exhibit troughs in trace element patterns for Hf, Nb, Ta and Cs that are diminished or eliminated at higher degrees of melting. Apart from these features and larger LREE/HREE ratios, trace element compositions are similar to silicate melts of peridotite in CO2-free conditions.
Partial melting of magnesite-bearing peridotites was studied at 610 GPa and 1300-1700 degrees C. Experiments were performed in a multianvil apparatus using natural mineral mixes as starting material placed into olivine containers and sealed in Pt capsules. Partial melts originated within the peridotite layer, migrated outside the olivine container and formed pools of quenched melts along the wall of the Pt capsule. This allowed the analysis of even small melt fractions. Iron loss was not a problem, because the platinum near the olivine container became saturated in Fe as a result of the reaction Fe2SiO4Ol = Fe-FePt alloy + FeSiO3Opx + O-2. This reaction led to a gradual increase in oxygen fugacity within the capsules as expressed, for example, in high Fe3+ in garnet. Carbonatitic to kimberlite-like melts were obtained that coexist with olivine + orthopyroxene + garnet +/- clinopyroxene +/- magnesite depending on P-T conditions. Kinetic experiments and a comparison of the chemistry of phases occasionally grown within the melt pools with those in the residual peridotite allowed us to conclude that the melts had approached equilibrium with peridotite. Melts in equilibrium with a magnesite-bearing garnet lherzolite are rich in CaO (2025 wt%) at all pressures and show rather low MgO and SiO2 contents (20 and 10 wt%, respectively). Melts in equilibrium with a magnesite-bearing garnet harzburgite are richer in SiO2 and MgO. The contents of these oxides increase with temperature, whereas the CaO content becomes lower. Melts from magnesite-free experiments are richer in SiO2, but remain silicocarbonatitic. Partitioning of trace elements between melt and garnet was studied in several experiments at 6 and 10 GPa. The melts are very rich in incompatible elements, including large ion lithophile elements (LILE), Nb, Ta and light rare earth elements. Relative to the residual peridotite, the melts show no significant depletion in high field strength elements over LILE. We conclude from the major and trace element characteristics of our experimental melts that primitive kimberlites cannot be a direct product of single-stage melting of an asthenospheric mantle. They rather must be derived from a previously depleted and re-enriched mantle peridotite.
During ascent, kimberlites react with the lithospheric mantle, entrain and assimilate xenolithic material, loose volatiles and suffer from syn- and post-magmatic alteration. Consequently, kimberlite rocks deviate heavily from their primary melt. Experiments at 7 GPa, 1300–1480 °C, 10–30 wt% CO2 and 0.46 wt% H2O on a proposed primitive composition from the Jericho kimberlite show that saturation with a lherzolitic mineral assemblage occurs only at 1300–1350 °C for a carbonatitic melt with <8 wt% SiO2 and >35 wt% CO2. At asthenospheric temperatures of >1400 °C, where the Jericho melt stays kimberlitic, this composition saturates only in low-Ca pyroxene, garnet and partly olivine.
We hence forced the primitive Jericho kimberlite into multiple saturation with a lherzolitic assemblage by adding a compound peridotite. Saturation in olivine, low- and high-Ca pyroxene and garnet was obtained at 1400–1650 °C (7 GPa), melts are kimberlitic with 18–29 wt% SiO2 + Al2O3, 22.1–24.6 wt% MgO, 15–27 wt% CO2 and 0.4–7.1 wt% H2O; with a trade-off of H2O vs. CO2 and temperature. Melts in equilibrium with high-Ca pyroxene with typical mantle compositions have ≥2.5 wt% Na2O, much higher than the commonly proposed 0.1–0.2 wt%.
The experiments allow for a model of kimberlite origin in the convective upper mantle, which only requires mantle upwelling that causes melting at the depth where elemental carbon (in metal, diamond or carbide) converts to CO2 (at ∼250 km). If primary melts leading to kimberlites contain a few wt% H2O, then adiabatic temperatures of 1400–1500 °C would yield asthenospheric mantle melts that are kimberlitic (>18 wt% SiO2 + Al2O3) but not carbonatitic (<10 wt% SiO2 + Al2O3) in composition, carbonatites only forming 100–200 °C below the adiabat. These kimberlites represent small melt fractions concentrating CO2 and H2O and then acquire part of their chemical signature by assimilation/fractionation during ascent in the subcratonic lithosphere.
