Showing papers on "Archean published in 2022"
TL;DR: The authors reported abyssal peridotites with melt-depletion ages up to 2.8 Ga, documented by extremely unradiogenic 187Os/188Os ratios (to as low as 0.1095) and refractory major elements that compositionally resemble the deep keels of Archean cratons.
Abstract: Basalts and mantle peridotites of mid-ocean ridges are thought to sample Earth’s upper mantle. Osmium isotopes of abyssal peridotites uniquely preserve melt extraction events throughout Earth history, but existing records only indicate ages up to ~2 billion years (Ga) ago. Thus, the memory of the suspected large volumes of mantle lithosphere that existed in Archean time (>2.5 Ga) has apparently been lost somehow. We report abyssal peridotites with melt-depletion ages up to 2.8 Ga, documented by extremely unradiogenic 187Os/188Os ratios (to as low as 0.1095) and refractory major elements that compositionally resemble the deep keels of Archean cratons. These oceanic rocks were thus derived from the once-extensive Archean continental keels that have been dislodged and recycled back into the mantle, the feasibility of which we confirm with numerical modeling. This unexpected connection between young oceanic and ancient continental lithosphere indicates an underappreciated degree of compositional recycling over time.
23 citations
01 Feb 2022
TL;DR: In this article, the authors argue that the mechanism of magma emplacement has generally been passive at all stages of Earth evolution and that most of the magmatism related to subduction, rifting, mid-oceanic spreading, flood basalts and large igneous provinces and related to mantle upwellings, magma underplating, slab windows, orogenic collisions as well as Archean TTG formation are predominantly passive from the lithosphere-scale to the crystal-scale.
Abstract: Magmatism has occurred throughout Earth's history. From the early Earth to the modern plate-tectonic Earth, the amount of magmatism has varied, but it has always occurred on multiple scales, in various tectonic environments and at various depths in the crust and mantle. Magma compositions also vary. In this paper, we argue that the mechanism of magma emplacement has generally been passive at all stages of Earth evolution. We conclude that most magmatism related to subduction, rifting, mid-oceanic spreading, flood basalts and large igneous provinces and related to mantle upwellings, magma underplating, slab windows, orogenic collisions as well as Archean TTG formation are predominantly passive from the lithosphere-scale to the crystal-scale. Our results weigh against the view that magmatism drives plate motions. Most of the magmatism on other Earth-like planets is also passive regardless of the tectonic environments.
21 citations
TL;DR: In this article , an Archean orogenic eclogite was found to have reached at least 65 to 70 km in depth at circa 2.5 Ga. This extends the known age of subduction-related eclogi-facies metamorphism back 400 My, showing that modern-style plate tectonics operated by the close of the Archean.
Abstract: Significance The onset time of plate tectonics is highly debated in the Earth sciences. A key indicator of modern-style plate tectonics, with deep subduction of oceanic plates, is the presence of eclogite (oceanic crust metamorphosed at high-pressure and low-temperature) in orogenic belts. Since no orogenic eclogites older than 2.1 billion y are currently documented, many scientists argue that modern plate tectonics started only 2.1 billion y ago (Ga). We document an Archean orogenic eclogite, providing robust evidence that subduction of oceanic crust reached to at least 65 to 70 km in depth at circa 2.5 Ga. This extends the known age of subduction-related eclogite-facies metamorphism back 400 My, showing that modern-style plate tectonics operated by the close of the Archean.
19 citations
18 citations
TL;DR: In this article , the authors compare the geochemistry of Archean volcanic rocks with that of Phanerozoic arc volcanic rocks and conclude that the latter formed in arc-related settings by modern-style plate tectonic processes that operated throughout the Archean.
17 citations
TL;DR: In this paper , a detailed analysis of gravity field over these areas, and their possible relationship with lithospheric thickness variations was presented, showing a large variation in residual gravity field among the different cratons.
Abstract: The nature of crust and lithospheric mantle evolution of the Archean shields and their subsequent destruction through intraplate tectonic processes are important in understanding continental dynamics and resources. The Indian shield, which has remained dynamic throughout the past for more than three billion years of geological history, is unique in terms of its lithospheric architecture compared to other Archean terranes on the globe. It consists of five major cratons, the Dharwar, Singhbhum, Bundelkhand, Bastar and Aravalli, which are separated by active rift valleys, mega lineaments and sutures zones. Here, we present a detailed analysis of gravity field over these areas, and their possible relationship with lithospheric thickness variations. Our results show a large variation in residual gravity field among the different cratons. A highly negative anomaly of around -70 mGal occurs over the western part of the Dharwar Craton, beneath which the lithosphere is about 160–200 km thick. In comparison, the anomalies are conspicuously positive, reaching around (i) +10 mGal over Central Dharwar Craton, Eastern Ghats Belt and the eastern part of Singhbhum Craton, (ii) +35 mGal over the Nellore Schist and Aravalli-Delhi Fold Belts, and (iii) +60 to +70 mGal over eastern part of SGT. In these regions, the lithosphere is markedly thinner between 70 and 135 km. Such areas have been associated with episodic magmatism, moderately high heat flow and elevated Moho temperatures, indicating a large-scale upwarping of isotherms leading to lithospheric destruction to the tune of 100–150 km, caused by mechanical, thermal and chemical erosion. Our study confirms that many of the Archean cratons on the globe, like the Indian shield, have undergone substantial erosion of their roots through subsequent geotectonic processes.
14 citations
01 Feb 2022
TL;DR: In this paper, a global compilation of structural, lithological, and geochemical data on a selection of Archean, Proterozoic and Phanerozoic magmatic complexes, interpreted as ophiolites, is presented.
Abstract: A global compilation of structural, lithological, and geochemical data on a selection of Archean, Proterozoic and Phanerozoic magmatic complexes, interpreted as ophiolites, is presented. Ophiolites, based on Phanerozoic examples, can be classified into subduction-related and subduction unrelated categories. These categories can be further subdivided into several subtypes depending on the proximity to subduction zones, and on sequential development from rifting – drifting to seafloor spreading for the subduction-unrelated category. From bottom to top ophiolites exhibit a magmatic sequence of ultramafic rocks (upper mantle units), gabbros (layered and isotropic), basaltic dikes and lavas, as well as boninites and felsic dikes and lavas in the subduction-related types. Archean greenstone belts show large variations in their construction, but Eoarchean examples display identical structure and lithology to the Phanerozoic ophiolites, attesting to the operation of seafloor spreading and subduction zone processes in the early Earth's history. Lithological differences between the Archean and Proterozoic/Phanerozoic ophiolites are demonstrated in the common occurrence of komatiites and felsic rocks, and scarcity of sheeted dike complexes in the former, compared to the opposite situation in those ophiolites that are younger than ca. 2 Ga. Geochemically there is a concomitant decrease in the content of incompatible elements (e.g., Sr, Zr, Y, Nb) and an increase in the content of compatible elements (e.g., Mg, Cr, Ni). In terms of tectonic environment analyzes, the Archean ophiolites are more abundantly subduction-related than those of Proterozoic and Phanerozoic ages. The subduction-dominant Archean oceanic crust (ophiolites) was characterized by accretionary cycle plate tectonics, whereas for those of Proterozoic and Phanerozoic ages, a combination of both accretionary cycle and Wilson cycles plate tectonic processes was operative.
14 citations
TL;DR: In this article , it was shown that plate tectonic processes characterized by subduction and arc magmatism have been in operation at least as long as recorded by the preserved geologic record, since the Eoarchean.
Abstract: Earth’s continental crust has grown and been recycled throughout geologic history along convergent plate margins. The main locus of continental crustal growth is in intra-oceanic and continental-margin arc systems in Archean time. In arc systems, oceanic lithosphere is subducted to the deeper mantle, and together with its overlying sedimentary sequence is in some cases off-scraped to form accretionary prisms. Fluids are released from the subducting slab to chemically react with the mantle wedge, forming mafic-ultramafic metasomatites, whose partial melting generates mafic melts that rise up to form arcs. In intra-oceanic arcs, they produce dominantly basaltic lavas, with a mid-crust that includes variably-developed vertically-walled intermediate plutons and higher-level dikes and sills. In continental-margin arcs, different petrogenetic processes cause assimilation and fractionation of basaltic magmas, partial melting/reworking of juvenile basaltic rocks, and mixing of mantle- and crust-derived melts, so they produce andesitic calc-alkaline melts but still have a mid-crust dominated by vertically-walled felsic plutons, which form 3-D dome-and-basin structures, akin to those in some Archean terranes such as parts of the Pilbara and Zimbabwe cratons. Notably, the continental crust of Archean times is dominated by tonalite-trondhjemite-granodiorite (TTG) plutons, similar to that of the mid-crust of these arc systems, suggesting that early continental crust may have formed largely by the amalgamation of multiple arc systems. The patterns of magmatism, in terms of petrogenesis, rock types, duration of magmatic and accretionary events, and the spatial scales of deformation and magmatism have remained essentially the same throughout geological history, demonstrating that plate tectonic processes characterized by subduction and arc magmatism have been in operation at least as long as recorded by the preserved geologic record, since the Eoarchean. However, the early Earth was dominated by accretionary orogens and oceanic arcs, that gradually grew thicker through multiple accretion events to form early continental-margin arcs by 3.5–3.2 Ga, and accretionary orogens. Slab melting and warmer metamorphism was more common in Archean arc systems due to higher mantle temperatures. These early arcs were further amalgamated into large emergent continents by ∼3.2–3.0 Ga, allowing large-scale processes such as lithospheric rifting and continental collisions, and the start of the supercontinent cycle. Further work should apply the null hypothesis, that plate tectonics explains the geologic record, to test for differences in the style of plate tectonics and magmatism through time, based on the fundamental difference in planetary heat production and the evolution of rotational dynamics of the Earth-Sun-Moon system.
14 citations
TL;DR: In this paper , a global compilation of structural, lithological, and geochemical data on a selection of Archean, Proterozoic and Phanerozoic ophiolites, interpreted as ophiliites, is presented.
Abstract: • Global compilation of the salient features of ophiolites. • Lithological differences between Archean and Proterozoic/Phanerozoic ophiolites. • Subduction-dominant Archean oceanic crust with accretionary cycle plate tectonics. • For Proterozoic and Phanerozoic a combination of both accretionary cycle and Wilson cycles. A global compilation of structural, lithological, and geochemical data on a selection of Archean, Proterozoic and Phanerozoic magmatic complexes, interpreted as ophiolites, is presented. Ophiolites, based on Phanerozoic examples, can be classified into subduction-related and subduction unrelated categories. These categories can be further subdivided into several subtypes depending on the proximity to subduction zones, and on sequential development from rifting – drifting to seafloor spreading for the subduction-unrelated category. From bottom to top ophiolites exhibit a magmatic sequence of ultramafic rocks (upper mantle units), gabbros (layered and isotropic), basaltic dikes and lavas, as well as boninites and felsic dikes and lavas in the subduction-related types. Archean greenstone belts show large variations in their construction, but Eoarchean examples display identical structure and lithology to the Phanerozoic ophiolites, attesting to the operation of seafloor spreading and subduction zone processes in the early Earth's history. Lithological differences between the Archean and Proterozoic/Phanerozoic ophiolites are demonstrated in the common occurrence of komatiites and felsic rocks, and scarcity of sheeted dike complexes in the former, compared to the opposite situation in those ophiolites that are younger than ca. 2 Ga. Geochemically there is a concomitant decrease in the content of incompatible elements (e.g., Sr, Zr, Y, Nb) and an increase in the content of compatible elements (e.g., Mg, Cr, Ni). In terms of tectonic environment analyzes, the Archean ophiolites are more abundantly subduction-related than those of Proterozoic and Phanerozoic ages. The subduction-dominant Archean oceanic crust (ophiolites) was characterized by accretionary cycle plate tectonics, whereas for those of Proterozoic and Phanerozoic ages, a combination of both accretionary cycle and Wilson cycles plate tectonic processes was operative.
13 citations
TL;DR: In this article , the authors report the first comprehensive documentation of the textures and inclusions of an Archean (circa 2.55 Ga) podiform chromitite from an orogenic ophiolitic mélange in China, recording an ancient CHONSP cycle.
13 citations
TL;DR: A comprehensive review of U-Pb and Lu-Hf spot analyses in zircon provides new insights on the pre-Brasiliano crustal growth of the main tectonic domains of the southern South American Platform from the Archean to the early Neoproterozoic as mentioned in this paper .
TL;DR: In this article , a global compilation of ∼3.8-2.5 Ga basalts can be subdivided into groups B-1 and B-2, showing modern mid-ocean ridge basalt-like features.
Abstract: The redox evolution of Archean upper mantle impacted mantle melting and the nature of chemical equilibrium between mantle, ocean and atmosphere of the early Earth. Yet, the origin of these variations in redox remain controversial. Here we show that a global compilation of ∼3.8-2.5 Ga basalts can be subdivided into group B-1, showing modern mid-ocean ridge basalt-like features ((Nb/La)PM ≥ 0.75), and B-2, which are similar to contemporary island arc-related basalts ((Nb/La)PM < 0.75). Our V-Ti redox proxy indicates a more reducing upper mantle, and the results of both ambient and modified mantle obtained from B-1 and B-2 samples, respectively, exhibit a ∼1.0 log unit increase in their temporal evolution for most cratons. Increases in mantle oxygen fugacity are coincident with the changes in basalt Th/Nb ratios and Nd isotope ratios, indicating that crustal recycling played a crucial role, and this likely occurred either via plate subduction or lithospheric drips.
TL;DR: In this paper , a consistent framework of craton evolution during the Archaean is proposed that aims to put to rest some of the uncertainties on its geological history, based on a critical literature review, and aided by new field and geochronological data.
03 May 2022
TL;DR: In this paper , the results of 167 calcite twinning strain analyses (131 limestones and 36 calcite veins, n = 7368 twin measurements) from the Teton-Gros Ventre (west; n = 21), Wind River (n = 43), Beartooth (n= 32), Bighorn and Black Hills (east); n = 11) Laramide uplifts were reported.
Abstract: ABSTRACT We report the results of 167 calcite twinning strain analyses (131 limestones and 36 calcite veins, n = 7368 twin measurements) from the Teton–Gros Ventre (west; n = 21), Wind River (n = 43), Beartooth (n = 32), Bighorn (n = 32), and Black Hills (east; n = 11) Laramide uplifts. Country rock limestones record only a layer-parallel shortening (LPS) strain fabric in many orientations across the region. Synorogenic veins record both vein-parallel shortening (VPS) and vein-normal shortening (VNS) fabrics in many orientations. Twinning strain overprints were not observed in the limestone or vein samples in the supracrustal sedimentary veneer (i.e., drape folds), thereby suggesting that the deformation and uplift of Archean crystalline rocks that form Laramide structures were dominated by offset on faults in the Archean crystalline basement and associated shortening in the midcrust. The twinning strains in the pre-Sevier Jurassic Sundance Formation, in the frontal Prospect thrust of the Sevier belt, and in the distal (eastern) foreland preserve an LPS oriented approximately E-W. This LPS fabric is rotated in unique orientations in Laramide uplifts, suggesting that all but the Bighorn Mountains were uplifted by oblique-slip faults. Detailed field and twinning strain studies of drape folds identified second-order complexities, including: layer-parallel slip through the fold axis (Clarks Fork anticline), attenuation of the sedimentary section and fold axis rotation (Rattlesnake Mountain), rotation of the fold axis and LPS fabric (Derby Dome), and vertical rotations of the LPS fabric about a horizontal axis with 35% attenuation of the sedimentary section (eastern Bighorns). Regional cross sections (E-W) across the Laramide province have an excess of sedimentary veneer rocks that balance with displacement on a detachment at 30 km depth and perhaps along the Moho discontinuity at 40 km depth. Crustal volumes in the Wyoming Province balance when deformation in the western hinterland is included.
TL;DR: Using structural, metamorphic phase equilibria, chronological and geochemical investigations, the authors reconstructs the tectonic evolution of the Chottanagpur Gneiss Complex (CGC) as a distinct crustal block at the eastern end of the Greater Indian Proterozoic Fold Belt (GIPFOB) along which the North India Block and the South India Block (SIB) accreted.
Abstract: In paleogeographic reconstructions of the Columbia and Rodinia Supercontinents, the position of the Greater India landmass is ambiguous. This, coupled with a limited understanding of the tectonic evolution of the mobile belts along which the mosaic of crustal domains in India accreted, impedes precise correlation among the dispersed crustal fragments in supercontinent reconstructions. Using structural, metamorphic phase equilibria, chronological and geochemical investigations, this study aims to reconstruct the tectonic evolution of the Chottanagpur Gneiss Complex (CGC) as a distinct crustal block at the eastern end of the Greater Indian Proterozoic Fold Belt (GIPFOB) along which the North India Block (NIB) and the South India Block (SIB) accreted. The study focuses on two issues, e.g. dating the Early Neoproterozoic (0.92 Ga) accretion of the CGC with the NIB contemporaneous with the assembly of Rodinia, and documenting the widespread (>24,000 km2) plutonism of 1.5–1.4 Ga weakly peraluminous, calc-alkalic to alkali-calcic and ferroan A-type granitoids (± garnet) devoid of mafic microgrannular enclaves and coeval mafic emplacements in the crustal block. These dominantly within-plate granitoids arguably formed by asthenospheric upwelling induced partial melting of garnet-bearing anatectic quartzofeldspathic gneisses that dominate the Early Mesoproterozoic basement of the block. The major and trace element chemistry of the granitoids is similar to the 1.35–1.45 Ga A-type granitoids in Laurentia/Amazonia emplaced contemporaneous with the 1.5–1.3 Ga breakup of the Columbia Supercontinent. This study suggests the Chottanagpur Gneiss Complex occured as a fragmented crustal block following the breakup of the Columbia Supercontinent; the crustal block was subsequently integrated within India during the Early Neoproterozoic oblique accretion between the NIB and SIB contemporaneous with the Rodinia Supercontinent assembly.
TL;DR: In this article , the authors show that the δ18O of igneous zircon in preserved rocks varies greatly from the detrital zircan record over time, both in terms of the magnitude of δ 18O and the secular variation.
TL;DR: Giant quartz veins are widespread on the Bundelkhand Craton of the Indian Shield which precise ages with a SHRIMP-II, U-Th-Pb isotope are quantified in this article .
Abstract: Giant quartz veins are widespread on the Bundelkhand Craton of the Indian Shield which precise ages with a SHRIMP-II, U-Th-Pb isotope are quantified in this article. Their relative geological age is well-documented: they cut the Paleoproterozoic (2150–1800 Ma) sediments of the Bijawar Group and are overlain by Proterozoic (1670–1030 Ma) sediments at the base of the Upper Vindhyan Supergroup. U-Th-Pb dating of zircon grains from a quartz vein was carried out to assess major event of their formation as 1866 ± 12 Ma. This data is consistent with the relative geological age of the veins. In addition, the quartz veins were shown to contain 2.86, 2.7, and 2.54 Ga xenocrystic zircon grains. Rocks with these ages are abundant in the craton. The formation of a giant quartz vein swarm is associated with the deformation of the Bundelkhand Craton lithosphere during 1.9–1.8 Ga ago triggered by compression caused by collision processes at the western flank of the Columbia Supercontinent on one side and plume activity on the other.
TL;DR: In this article, the authors show that the δ 18 O of igneous zircon in preserved rocks varies greatly from the detrital zircan record over time, both in terms of the magnitude of δ18 O and the secular variation.
TL;DR: The authors measured the phosphate concentrations of 2.8-2.5 Ga shallow marine carbonate facies across six Neo-archean shelf-ramp environments and found that stromatolites, micrites, and crystal fans were >4-fold to 12-fold more enriched in carbonate-associated phosphate than modern marine coral skeletons and abiotic Phanerozoic carbonates.
Abstract: Phosphorus is essential for cell biology, yet scarce in modern marine environments wherein free phosphate is consumed by life or titrated by calcium to form apatite minerals. The environmental conditions under which the early biosphere emerged and phosphorus was integrated throughout biochemistry is yet unknown. We measured the phosphate concentrations of 2.8–2.5 Ga shallow marine carbonate facies across six Neoarchean shelf-ramp environments. We found that the P/Ca ratios of Neoarchean stromatolites, micrites, and crystal fans were >4-fold to 12-fold more enriched in carbonate-associated phosphate than modern marine coral skeletons and abiotic Phanerozoic carbonates. Our results support the view that Archean productivity was limited by the availability of electrons rather than phosphate or other nutrients, and help explain why phosphorus is so central to the molecules, metabolisms, and bioenergetics observed in cells.
TL;DR: In this article , a comprehensive compilation of published 2.50−2.20 Ga magmatism in the North China Craton (NCC) is presented to provide key constraints on the Archean-Proterozoic transition.
TL;DR: In this paper , a high-precision 182W dataset for rocks from the Kaapvaal Craton, southern Africa, revealing the presence of Hadean protocrustal remnants in Earth's mantle.
Abstract: SignificanceDue to active plate tectonics, there are no direct rock archives covering the first ca. 500 million y of Earth's history. Therefore, insights into Hadean geodynamics rely on indirect observations from geochemistry. We present a high-precision 182W dataset for rocks from the Kaapvaal Craton, southern Africa, revealing the presence of Hadean protocrustal remnants in Earth's mantle. This has broad implications for geochemists, geophysicists, and modelers, as it bridges contrasting 182W isotope patterns in Archean and modern mantle-derived rocks. The data reveal the origin of seismically and isotopically anomalous domains in the deep mantle and also provide firm evidence for the operation of silicate differentiation processes during the first 60 million y of Earth's history.
TL;DR: In this article , the authors use the Ge/Si ratio as a complementary tracer to δ30Si in order to delineate the exact role of modal quartz and silicified basalts from the Archean seafloor among the primary controls of the early appearance of felsic melts on Earth.
TL;DR: In this paper , a set of Sm-Nd, Lu-Hf, Re-Os, and Hf-W isotope and lithophile and siderophile element abundance data for komatiites and basalts were presented.
TL;DR: Petrographic and geochemical characteristics of quartzites from Simlipal Complex coupled with U-Pb ages of detrital zircons and zircon geochemistry to understand the provenance and depositional conditions and its connection with the crustal stabilization in the Singhbhum Craton as mentioned in this paper.
Abstract: Cratonic stabilization was a critical crustal process during the Hadean to Archean for the formation of cratons. The understanding of how and where this process took place is significant to evaluate the architecture of continents. The Singhbhum Craton of eastern India has well preserved Precambrian volcano-sedimentary sequences. The Simlipal volcano-sedimentary complex of Singhbhum Craton consists of circular bands of mafic volcanic rocks interlayered with quartzites/ shales/phyllites. In the present study, we report petrographic and geochemical characteristics of quartzites from Simlipal Complex coupled with U–Pb ages of detrital zircons and zircon geochemistry to understand the provenance and depositional conditions and its connection with the crustal stabilization in the Singhbhum Craton. The quartzites are texturally mature with sub-angular to sub-rounded quartz grains followed by feldspars embedded in a silty matrix. Based on modal compositions and major element ratios, these quartzites are categorized as quartz arenite and sub-lithic arenites. Trace element abundances normalized to Archean Upper Continental Crust (AUCC) display positive anomalies at U, Zr, Hf and negative anomalies at Nb. REE patterns are characterized by negative Eu anomalies (Eu/Eu* = 0.47–0.97) and flat HREE suggesting felsic provenance. These quartzites show depletion of LILE, enrichment of HFSE and transition metals relative to AUCC. High weathering indices such as CIA, PIA, and ICV are suggestive of moderate to intense chemical weathering. Low trace element ratios such as Th/Cr, Th/Sc, La/Sc, La/Co and Th/Co indicate a predominantly felsic source for these rocks. The overall geochemical signatures indicate passive margin deposition for these quartzites. Detrital zircons from the Simlipal quartzites yield U–Pb ages 3156 ± 31 Ma suggesting Mesoarchean crustal heritage. The trace element geochemistry of detrital zircons suggests that the zircons are magmatic in origin and possibly derived from the 3.1 Ga anorogenic granite/granitoid provenance of Singhbhum Craton. These observations collectively indicate the Mayurbhanj Granite and Singhbhum Granite (SBG-III) provenance for these quartzites, thereby tracking the stabilization of the eastern Indian Shield/Singhbhum Craton back to Mesoarchean.
TL;DR: In this paper , the authors presented a revised interpretation of the history of atmospheric oxygen in the Archean and Proterozoic, based on a multi-geochemical proxy approach.
Abstract: The great oxygenation event (GOE), the first of two major rises in atmospheric oxygen in Earth history, was initially placed near the Archean-Proterozoic boundary (∼2500 Ma). More recently, the position of the GOE has been moved to between 2500 and 2300 Ma so as to coincide with the loss of the MIF sulfur isotope signal due to the creation of the Earth's ozone layer at that time. Here we present a revised interpretation of the history of atmospheric oxygen in the Archean and Proterozoic, based on a multi-geochemical proxy approach. Integration of a large database of analyses of redox sensitive elements in sedimentary pyrite (Se, Co, Mo), the matrix of black shales (U, Mo), and the temporal evolution of redox sensitive minerals, suggest Earth's first oxygenation was prolonged, reaching a peak between 2000 and 1700 Ma. Rather than a relatively short-lived event from 2500 to 2300 Ma, we suggest an alternative profile for Earth's atmospheric O2, i.e., an unsteady start to the rise in oxygen around 2700 Ma that undulated for approximately a billion years, reaching a peak around 1900 Ma before a plunge in the Proterozoic Eon after 1700 Ma.
TL;DR: The use of the term "proto-subduction" has been criticised by as mentioned in this paper , who argue that Benioff-type subduction is only one of a spectrum of mechanisms that have operated through time for the foundering and recycling of lithosphere into the mantle.
TL;DR: In this paper , the authors present new data on Fe isotope and trace element chemistry for 3.4-3.5 Ga jaspilites from the North Pole region of the Pilbara Craton, including the first example of a land-sea transition preserved in the lower Dresser Formation as jaspile deposition in restricted basin and open-marine settings.
TL;DR: In this article , the authors analyzed granitoids distributed throughout the Archean Yilgarn Craton of Western Australia and found that most of them carry MIF-S signatures.