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The juvenile Neoproterozoic basement of the Arabian Shield is overlain with angular unconformity by a voluminous Cambro-Ordovician cover sequence known as the Saq Formation and Wajid Group. Provenance studies of this vast siliciclastic cover over the Saudi Arabian part of the Arabian-Nubian Shield (ANS) have to date been based solely on U-Pb zircon data and heavy minerals. We present the first combined in-situ U-Pb, δ18O and Lu-Hf isotopic data for detrital zircon from the Saq and Wajid units exposed along the northeastern margin and southern part of the Arabian Shield. U-Pb age spectra reveal prominent age peaks at ca. 0.8–0.55 Ga and 1.1–0.9 Ga with subordinate peaks at ca. 2.2–1.7 Ga and 2.7–2.5 Ga. The δ18O secular variation mirrors global compilations with Archaean zircon defining a restricted δ18O range of ca. 4.0–8.0 ‰ and younger zircon showing wide variation in δ18O up to ca. 14 ‰. The ca. 0.8–0.55 Ga age peak has the largest variation in εHf(t) with about half of all these Neoproterozoic zircon grains being juvenile (εHf(t) > 5), which are interpreted to be sourced from the juvenile terranes of the ANS. Neoproterozoic zircon with evolved εHf(t) signatures require a more distal source beyond the ANS. As extensive ca. 1.1–0.9 Ga crust is lacking in the vicinity of the ANS, the ca. 1.1–0.9 Ga age peak is interpreted to be derived from either contemporaneous orogenic belts in Central Africa or recycled from older sedimentary rocks containing these age components. Extreme variations in δ18O of post–Archaean zircon, together with the evolved εHf(t), indicate crustal thickening and increased incorporation of supracrustal material associated with collisional orogenesis. The remarkable similarities in age spectra and isotopic compositions of the Saq Formation and Wajid Group sandstones with those from other regions in northern Gondwana indicate a continental–scale homogenization and dispersion process. [ABSTRACT FROM AUTHOR]

[Display omitted] • Six major global geological records are analyzed by Spearman's correlation. • Acceleration of the supercontinent cycle best fits global geological records. • The supercontinent cycle could be the major process driving plate tectonics evolution. 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 (ρ s). Ranking the GGDs according to Spearman's method allows them to be compared. Each GGD shows moderate to very strong correlations (0.5 < ρ s < 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 ρ s = 0.45), potentially supporting the supercontinent cycle as the first-order mechanism of plate tectonics evolution. Conversely, constant cyclicities result in weaker correlations (average ρ s < 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 ρ s = 0.04). The implications for the supercontinent cycle and the limits of Spearman's correlation are also discussed. [ABSTRACT FROM AUTHOR]

[Display omitted] • First report of whole rock Re-Os isotopic data of Neo-Tethyan mantle rocks from Indian ophiolites. • Sub-chondritic 187Os/188Os indicating primary depleted nature and subsequent melt percolation. • Trace and REE chemistry with Re addition corroborate multistage petrogenetic processes. • Recycling of SCLM fragments in depleted mantle linked with the Gondwana reconfiguration. Naga Hills Ophiolite (NHO) represents a thrusted section of relict Neo-Tethyan oceanic lithosphere comprising distinct crustal and upper mantle lithologies that preserve imprints of different stages of evolution of ancient ocean basins and subsequent accretion onto continental margins during late Cretaceous-Eocene collision involving Indian and Eurasian Plates. This study presents bulk geochemistry and Re-Os isotopic compositions for the mantle peridotites of NHO to address their petrogenetic aspects, implications for Neo-Tethyan upper mantle heterogeneity and thermo-tectonic evolution of Neo-Tethyan oceanic lithosphere through subduction-accretion-collision processes. Geochemical characteristics of the mantle peridotites, as reflected from their chondrite normalized REE patterns, binary relationship between fractionation depletion indices, low Re/Os, suggest that these are mantle residues resulting from ∼ 5–20 % of melt extraction from a spinel peridotite source that experienced decompression melting in a fore-arc extensional setting in response to subduction initiation. Isotopically, these mantle peridotites are subchondritic with 187Os/188Os (0.1218–0.1266) and γ Os values of −3.73 to −0.09 comparable with the depleted MORB source. LILE-LREE enrichment, HFSE depletion, and U-shaped chondrite-normalized REE patterns demonstrated by the studied samples with Re addition collectively corroborate multistage petrogenetic processes in compliance with geodynamic transition from extensional to compressional regime in a suprasubduction zone environment and partial melting of a chemically heterogeneous source mantle. This compositional heterogeneity can be equated with mantle depletion by melt extraction and refertilization by influx of slab-dehydrated fluids and percolation of boninitic melts. The non-radiogenic Os isotope signatures, negative γ Os values and wide spectrum of melt extraction ages for these mantle peridotites correspond to (i) multiple melt production and melt extraction events prior to the opening of Neo-Tethyan seaway (ii) detachment and incorporation of ancient, depleted SCLM fragments into oceanic mantle concurrent with subduction driven ocean basin closure-congregation of Gondwana Supercontinent and emergence of Neo-Tethyan embryonic ocean in response to disintegration of Gondwana Supercontinent. [ABSTRACT FROM AUTHOR]

[Display omitted] • Effect of the supercontinent cycle (SC) on the longest-term sea level is studied. • Various scenarios of the SC are tested in a conceptual model of continental drift. • Plate flattening effect is essential to recover realistic sea-level fluctuations. The longest-term (first-order) sea-level change is considered to be within ∼ 200–300 million years, which is roughly half or less of the period of the supercontinent cycle of ∼ 500–700 Myr. It is recognized that the assembly of supercontinents involves either the closure of the "interior ocean" that resulted from the breakup of the supercontinent or the closure of the "exterior ocean" that surrounded the supercontinent. The former process is termed "extroversion," while the latter is termed "introversion," both of which are an end-member scenario of the supercontinent cycle. A "combination" process is also proposed to explain the complex behavior of continental drift on the actual Earth. Despite recent advances in a time-dependent mantle convection model, some difficulties still remain in self-consistently recovering plate tectonics and continental drift of the past Earth. Therefore, it is worth addressing the fundamental physics of the effects of the history of plate motion and the associated continental drift on the longest-term sea-level change from the perspevtive of the supercontinent cycle in a timescale of the order of 100 million years. In this study, a simple conceptual model of mantle convection with various supercontinent cycle processes was constructed, and the effects of the supercontinent cycle on the longest-term sea-level change were addressed. The sea-level change is estimated from bathymetry over the oceanic plates under different free parameters that control the fluctuation of the sea-level change. The present analytical results suggest that the asymptotic bathymetry due to the plate flattening effect of oceanic plates in the exterior and interior oceans is essential to recover the realistic magnitude of sea-level fluctuations that is comparable to the sea-level curve of the past Earth. In addition, the absolute volume change in the seawater due to its recycling into the mantle may be important to fit the observed sea-level curves from stratigraphic studies since 200 million years ago. [ABSTRACT FROM AUTHOR]

The assembly and break-up of supercontinents have been hot research topics in international earth sciences because they represent a breakthrough in reconstructing the history of continental evolution and deepening the theory of plate tectonics, which is of indispensable importance to the development of earth sciences. With the continuous enrichment of paleomagnetic, paleontological, chronological, and geochemical data in the last two decades, the evolution of the supercontinent from Columbia to Rodinia has gradually gained unified understanding, and the reconstruction of the major plates within the supercontinent has basically been constrained. In contrast, the reconstruction of microplates, such as South China, Tarim, and Kabul, is controversial and has now become a popular topic and frontier area of supercontinent reconstruction. Hainan lies at the southern tip of South China, and a few Proterozoic units are exposed on the island. At present, Hainan is often taken as a part of the Cathaysia Block. However, due to the lack of exposed Mesoproterozoic igneous and supercrustal rocks in Cathaysia, the reconstruction model of the Cathaysia Block and even the South China Craton based solely on Mesoproterozoic units in Hainan are distinct from those based on units in the Yangtze Block and younger Proterozoic units within the Cathaysia Block, which makes the paleoposition of the South China Craton controversial. In this paper, we provide new detrital zircon U–Pb age data for the Baoban Complex, Hainan, together with the available data to comment on the affinities between Hainan and the Yangtze and Cathaysia Blocks in the Proterozoic, and on this basis, we can reconstruct the South China Craton within the Proterozoic supercontinents. [ABSTRACT FROM AUTHOR]

True polar wander (TPW), or planetary reorientation, is the rotation of solid Earth (crust and mantle) about the liquid outer core in order to stabilize Earth's rotation due to mass redistribution. Although TPW is well-documented on Earth presently with satellites and for multiple planets and moons in the Solar System, the prevalence of TPW in Earth history remains contentious. Despite a history of controversy, both the physical plausibility of TPW on Earth and an empirical basis for it are now undisputed. Lingering resistance to the old idea likely stems from the fact that, like plate tectonics, TPW may influence much of the Earth system, thus acknowledging its existence requires rethinking how many different datasets are interpreted. This review summarizes the development of TPW as a concept and provides a framework for future research that no longer regards TPW like a ghost process that may or may not exist, but as an integral part of the Earth system that can relate shallow and deep processes that are otherwise only mysteriously linked. Specifically, we focus on the temporal regularity of large TPW, and discuss its relationship with the supercontinent–megacontinent cycle based on previous studies. We suggest the assembly of mega-continents has a close linkage to large TPW. Meanwhile, supercontinent tenure and breakup have a close linkage to fast TPW. The effects of TPW on sea level changes, paleoclimate, biological diversity, and other facets of the Earth system are presented and require interdisciplinary tests in the future. [ABSTRACT FROM AUTHOR]

Chemical analyses of 1371 fluid inclusions in 131 halite samples with marine 87Sr/86Sr values were used to reconstruct the strontium concentrations [Sr] SW of Phanerozoic and Neoproterozoic seawater. [Sr] SW varied seven-fold and oscillated twice between high- and low-Sr concentrations over the past 550 million years (Myr), in rhythm with Ca-rich and SO 4 -poor paleoseawater intervals and calcite-aragonite seas. Variations in the [Sr]/[Ca] SW ratio from fluid inclusions were not significant over the past ∼270 Myr, and are within ±3 µmol/mmol of the modern [Sr]/[Ca] SW ratio of ∼8.5 µmol/mmol. These results agree with the [Sr]/[Ca] SW ratios obtained from fossil corals, benthic foraminifera, brachiopods, belemnites, and rudists. [Sr]/[Ca] SW in the early and middle Paleozoic was ∼2 times the modern [Sr]/[Ca] SW ratio. A major shift of the [Sr]/[Ca] SW ratio in the late Permian coincided with the initial rifting of the Pangean supercontinent. Seawater 87Sr/86Sr ratios plotted against 1/[Sr] SW show two distinct linear correlations: negative correlation from 515 to 252 Ma and positive correlation from 150 to 0 Ma, suggesting different controls on the global Sr cycle between these intervals. The negative correlation coincides with the long-term assembly of Pangea in the Paleozoic (∼500–250 Ma). The positive correlation from 150 to 0 Ma parallels the break-up of Pangea and the decrease of mid-ocean ridge (MOR) hydrothermal fluid flux and subduction zone length in the Mesozoic and Cenozoic. [ABSTRACT FROM AUTHOR]

We investigate the evolution of stress fields during the supercontinent cycle using the 2D Cartesian geometry model of thermochemical convection with the non-Newtonian rheology in the presence of floating deformable continents. In the course of the simulation, the supercontinent cycle is implemented several times. The number of continents considered in our model as a function of time oscillates around 3. The lifetime of a supercontinent depends on its dimension. Our results suggest that immediately before a supercontinent breakup, the over-lithostatic horizontal stresses in it (referring to the mean value by the computational area) are tensile and can reach −250 MPa. At the same time, a vast area beneath a supercontinent with an upward flow exhibits clearly the over-lithostatic compressive horizontal stresses of 50–100 МРа. The reason for the difference in stresses in the supercontinent and the underlying mantle is a sharp difference in their viscosity. In large parts of the mantle, the over-lithostatic horizontal stresses are in the range of ±25 MPa, while the horizontal stresses along subduction zones and continental margins are significantly larger. During the process of continent-to-continent collisions, the compressive stresses can approximately reach 130 MPa, while within the subcontinental mantle, the tensile over-lithostatic stresses are about −50 MPa. The dynamic topography reflects the main features of the supercontinent cycle and correlates with real ones. Before the breakup and immediately after the disintegration of the supercontinent, continents experience maximum uplift. During the supercontinent cycle, topographic heights of continents typically vary within the interval of about ±1.5 km, relatively to a mean value. Topographic maxima of orogenic formations to about 2–4 km are detected along continent-to-continent collisions as well as when adjacent subduction zones interact with continental margins.

Earth's known supercontinents are believed to have formed in vastly different ways, with two endmembers being introversion and extroversion. The former involves the closure of the internal oceans formed during the break-up of the previous supercontinent, whereas the latter involves the closure of the previous external superocean. However, it is unclear what caused such diverging behavior of supercontinent cycles that involved first-order interaction between subducting tectonic plates and the mantle. Here we address this question through 4D geodynamic modeling using realistic tectonic set-ups. Our results show that the strength of the oceanic lithosphere plays a critical role in determining the assembly path of a supercontinent. We found that high oceanic lithospheric strength leads to introversion assembly, whereas lower strength leads to extroversion assembly. A theoretically estimated reduction in oceanic crustal thickness, and thus its strength, during Earth's secular cooling indicates that introversion was only possible for the Precambrian time when the oceanic lithosphere was stronger, thus predicting the assembling of the next supercontinent Amasia through the closure of the Pacific Ocean instead of the Indian-Atlantic oceans. Our work provides a new understanding of the secular evolution of plate tectonics and geodynamics as the Earth cooled. [ABSTRACT FROM AUTHOR]

The assembly and break-up of supercontinents have been hot research topics in international earth sciences because they represent a breakthrough in reconstructing the history of continental evolution and deepening the theory of plate tectonics, which is of indispensable importance to the development of earth sciences. With the continuous enrichment of paleomagnetic, paleontological, chronological, and geochemical data in the last two decades, the evolution of the supercontinent from Columbia to Rodinia has gradually gained unified understanding, and the reconstruction of the major plates within the supercontinent has basically been constrained. In contrast, the reconstruction of microplates, such as South China, Tarim, and Kabul, is controversial and has now become a popular topic and frontier area of supercontinent reconstruction. Hainan lies at the southern tip of South China, and a few Proterozoic units are exposed on the island. At present, Hainan is often taken as a part of the Cathaysia Block. However, due to the lack of exposed Mesoproterozoic igneous and supercrustal rocks in Cathaysia, the reconstruction model of the Cathaysia Block and even the South China Craton based solely on Mesoproterozoic units in Hainan are distinct from those based on units in the Yangtze Block and younger Proterozoic units within the Cathaysia Block, which makes the paleoposition of the South China Craton controversial. In this paper, we provide new detrital zircon U–Pb age data for the Baoban Complex, Hainan, together with the available data to comment on the affinities between Hainan and the Yangtze and Cathaysia Blocks in the Proterozoic, and on this basis, we can reconstruct the South China Craton within the Proterozoic supercontinents.

The kinematics of the Paleoproterozoic assembly of Earth's first supercontinent, Nuna, are still debated. We present new paleomagnetic results from two Paleoproterozoic rock formations in the North Australia Craton (NAC) that exemplify cratonic assembly processes in the leadup to Nuna formation. Our new paleomagnetic data for the 1,825 Ma Plum Tree Creek Volcanics of the proto‐NAC and the layered mafic‐ultramafic 1,855 Ma Toby intrusion of the Kimberley Craton suggest their amalgamation just prior to ca. 1.8 Ga through a scissor‐like ocean closure to form the NAC, in accord with geological records. Comparing these new results with extant poles from Australia and other major cratons suggests similarly minor relative plate motions between ca. 1.9 and 1.65 Ga during craton and supercontinent formation. A global reconstruction suggests that these events could be related to a major slab‐suction event leading to Nuna formation. Plain Language Summary: Earth's evolution is characterized by the recurring assembly of most tectonic plates into one single supercontinent. There is mounting evidence that at least three supercontinents existed throughout Earth history. This cycle of supercontinents potentially played an important role for the evolution of life and is inextricably connected to plate tectonics. However, we still don't understand how and when exactly the supercontinent cycle initiated. We present here new paleomagnetic data allowing us the most precise paleogeographic reconstruction for the time interval before the first of the three known supercontinents formed. Our data reveals a small‐scale collisional assembly of the Australian cratons in the vicinity of the formation of other major cratons at that time. Our global reconstruction using the most up to date paleomagnetic data set can be interpreted as evidence for a model where all cratons formed over a mantle downwelling structure that ultimately lead to the initiation of the supercontinent cycle. Key Points: Two new high‐quality Paleoproterozoic paleopoles for the North Australian Craton are presentedThe new paleomagnetic data suggest a scissor‐like assembly of the North Australian CratonOur new kinematic model proposes a situation prior to the formation of the first supercontinent related to a major slab‐suction event [ABSTRACT FROM AUTHOR]

Earth's long‐term climate has been profoundly influenced by the episodic assembly and breakup of supercontinents at intervals of ca. 500 m.y. This reflects the cycle's impact on global sea level and atmospheric CO2 (and other greenhouse gases), the levels of which have fluctuated in response to variations in input from volcanism and removal (as carbonate) by the chemical weathering of silicate minerals. Supercontinent amalgamation tends to coincide with climatic cooling due to drawdown of atmospheric CO2 through enhanced weathering of the orogens of supercontinent assembly and a thermally uplifted supercontinent. Conversely, breakup tends to coincide with increased atmospheric CO2 and global warming as the dispersing continental fragments cool and subside, and weathering decreases as sea level rises. Supercontinents may also influence global climate through their causal connection to mantle plumes and large igneous provinces (LIPs) linked to their breakup. LIPs may amplify the warming trend of breakup by releasing greenhouse gases or may cause cooling and glaciation through sulfate aerosol release and drawdown of CO2 through the chemical weathering of LIP basalts. Hence, Earth's long‐term climatic trends likely reflect the cycle's influence on sea level, as evidenced by Pangea, whereas its influence on LIP volcanism may have orchestrated between Earth's various climatic states. [ABSTRACT FROM AUTHOR]

The North Purulia Shear Zone that dissects the granulite basement of the Chotanagpur Granite Gneissic Complex of the East Indian Shield exposes a deformed and metamorphosed nepheline syenite. The studied 'foid-monzosyenite' shows high abundances of large ion lithophile elements and high field strength elements with low abundances of compatible elements. Trace-element signatures show negative U, Th, Zr, Ti and Pb and positive Sr, Ba and Eu anomalies with respect to the primitive mantle. The chondrite-normalized diagram shows strongly fractionated rare earth element patterns ((La/Lu)N ∼23–87). Geochemical fingerprints suggest that the basanitic protolith was formed by low-degree partial melting of garnet peridotite in the sub-continental lithospheric mantle. The enriched large ion lithophile, high field strength element and light rare earth element concentrations (relative to primitive mantle) can be explained by a mixed mantle source with components from a previously deformed alkaline rock/carbonatite. Geochemical data do not support any significant crustal contamination and suggest variable fractionation of clinopyroxene, ilmenite, titanite and apatite from the parental melt. Petrological data are consistent with the view that the nepheline syenite magma was emplaced in a rift setting with a minimum temperature of 800–900°C, low fO2 conditions (below the fayalite–magnetite–quartz buffer) at a mid-crustal depth between 950 and 900 Ma. The continental rift zone, however, did not lead to the formation of an open ocean basin. Subsequently, the studied rock and its basement was deformed and metamorphosed in a continent–continent collisional setting at ∼900 Ma. Combining information from the other Indian occurrences with this study, it is demonstrated that the deformed alkaline rocks and carbonatite are potentially valuable for tracing the birth and demise of the palaeo-supercontinents. [ABSTRACT FROM AUTHOR]

[Display omitted] • Ore deposit formation as integral component of Earth's thermal and tectonic evolution and supercontinent cycles. • Ore deposits and their salient characteristics associated with the history of various supercontinents. • Influence of major events such as mantle overturn, GOE, Cambrian Explosion on ore mineral systems. • Relationship of mineral systems with evolution of the atmosphere-hydrosphere-biosphere system. Mineral systems with their core of ore deposits require a rare conjunction of geodynamic settings, crustal or lithospheric fertility, crustal architecture and suitable host rocks, and preservation potential. They are thus an integral component of Earth's thermal and tectonic evolution which also control the supercontinent cycles with progressive assembly and breakup of Ur, Kenorland, Columbia, Rodinia, Gondwana, and Pangea. Despite the ongoing debate, some form of plate tectonics has operated on Earth since the Eoarchean. However, the hotter Archean mantle generated a long-term double-layered convection system which was disrupted by episodic mantle overturns, with the largest in the early Neoarchean potentially enriching the mantle in metals that form the Earth's core. Cratons with thick subcontinental mantle lithosphere (SCLM) or tectosphere keels commenced to form in the Mesoarchean as small continents amalgamated. The conjunction of pre-4.0 Ga crust, giant Ti, Cr, Fe, Ni and PGE-enriched layered mafic intrusions and major diamond fields provide strong evidence that the Kaapvaal and Zimbabwe Cratons and Wyoming Craton formed part of Ur with its early potentially core-metal-fertilized SCLM. Orogenic gold deposits and VMS Cu-Zn-Pb deposits with their high preservation potential were deposited in subduction-related convergent margins that activated the assembly of all supercontinents with giant provinces related to assembly of Kenorland, Columbia and Gondwana-Pangea. Erosion-susceptible porphyry Cu-Au and epithermal Au-Ag deposits were most abundant at the time of Gondwana and Pangea and in Cenozoic convergent margins and collisional orogens, although there are rare examples associated with assembly of all supercontinents. Magmatic intrusion-related Ni-Cu-PGE, and magmatic-hydrothermal IOCG Cu-Au and Kiruna-type Fe-P deposits formed near craton margins. However, although giant Ni-Cu-PGE deposits formed during the breakup of all supercontinents, giant IOCG deposits were largely restricted to extensional episodes related to Kenorland and Columbia and Kiruna-type deposits to those involved in Columbia. The evolution of the Earth's atmosphere-hydrosphere-biosphere was an additional influence on that of the supercontinent cycle in terms of the evolution of metallogenic provinces. The Great Oxidation Event (GOE) at ca. 2.4–2.0 Ga witnessed the end of the great era of deposition of BIFs that became the hosts to high-grade Fe and Mn deposits which formed under more oxidizing conditions, with Oligocene sediment-hosted Mn deposits and late-Cenozoic Mn nodules becoming the dominant Mn resources and potential resource, respectively. The GOE was also responsible for the evolution of U deposits from the Mesoarchean paleoplacer uraninite deposits of the Witwatersrand, through Mesoproterozoic unconformity-related deposits to Phanerozoic sandstone roll deposits. The Cambrian 'explosion of life', following a second GOE event, magnified the importance of organisms, particularly those secreting Ca and Mg, carbonate in the formation or ore deposits in sedimentary basins. Late Paleoproterozoic-Mesoproterozoic shale-hosted SEDEX Zn-Pb-Cu deposits were progressively replaced by Phanerozoic carbonate-hosted MVT Pb-Zn deposits and Neoproterozoic-Cambrian Zambian-type Cu-Co deposits hosted in calcareous sedimentary sequences. Carlin-type Au-Ag deposits hosted by calcareous and carbonaceous sequences appeared in the Cretaceous to Paleogene epochs to rival the more ubiquitous orogenic gold deposits in terms of global importance. It is evident that the evolution of the great metallogenic belts of the Earth was intrinsically linked to the thermal and tectonic evolution of the Earth and particularly to plate tectonics and the supercontinent cycles. The nature of contained mineral deposits of elements with multiple valency states and those requiring particularly reactive host rocks was strongly influenced by the evolution of the atmosphere-hydrosphere-biosphere system. [ABSTRACT FROM AUTHOR]

[Display omitted] • Episodic crustal growth occurred in the microcontinents within the eastern CAOB. • Most of the continental crust in the microcontinents accreted in the Precambrian. • The varying rates of regional crustal growth are linked to supercontinent cycles. The crustal growth and reworking processes of accretionary orogen such as the Central Asian Orogenic Belt (CAOB) have been a controversial issue. Here, we present in situ zircon U–Pb and Lu–Hf isotopic data for granitoids from a microcontinent (the Songnen Massif) and an arc terrane (the Duobaoshan arc terrane), which generally represent two main crustal components in the eastern CAOB to establish a crustal growth model for an accretionary orogen and to trace the influence of the assembly and breakup of supercontinents on crustal evolution in an accretionary orogen. Neoproterozoic–Mesozoic granitoids distributed in the Songnen Massif show a step-like crustal growth pattern over time with three major periods of development: Paleoproterozoic crustal growth at 2.2–1.8 Ga, Mesoproterozoic growth at 1.6–1.0 Ga, and a third pulse of growth at 0.85–0.6 Ga, along with two short pauses at 1.8–1.6 Ga and 1.0–0.85 Ga. The assembly and collision phases of supercontinents corresponded to the enhanced and degressive crustal growth rates of the Songnen Massif, respectively, suggesting that the supercontinent cycles are responsible for the episodic crustal growth pattern in the region. Crustal reworking of the Songnen Massif occurred during 1000–180 Ma, with a fluctuation at 800–600 Ma, which provided a major contribution to the isotopic heterogeneity of lower continental crust. Isotopic compositions of granitoids from the Duobaoshan arc terrane located between the Xing'an and Songnen massifs, together with those of granitoids from other microcontinents, suggest that most of the continental crust beneath the microcontinents in the eastern CAOB generated during the Precambrian, whereas a significant amount of lateral crustal accretion occurred in continental arc settings during orogenies and amalgamation of microcontinents during the Phanerozoic. [ABSTRACT FROM AUTHOR]

The distribution of rare earth element (REE) deposits and their resources through geological time has been analyzed. The analysis is based on data on 103 deposits distributed around the world with a resource estimate of at least 100 000 t of lanthanoid and yttrium oxides. The variability in the formation of significant REE accumulations through geological time is demonstrated by comparing supercontinent cycles based on the ore resources of different types and ages. In the Kenoran cycle, only one deposit was identified in which the REE resources quantitatively exceeded the specified limit: a modified paleoplacer with initially detrital U–REE mineralization. The placer type is also represented in the Amasian cycle, but by deposits with different ore specialization. Carbonatite, hypergene in carbonatites, syenite, and alkali-granitic types are represented by deposits in all other supercontinent cycles. Significant foidic-type deposits were formed in the Columbian, Rodinian, and Pangean cycles; subalkali-granitic type deposits were formed, in the Columbian and Rodinian cycles; and ion-adsorption orebodies are known only in the Amasian cycle. On the geological time scale, deposits of all types are distributed very unevenly. The maximum resources are estimated in deposits of the Rodinian cycle. The other cycles, not counting the extremely nonproductive Kenoran cycle, are 2–2.5 times inferior to the Rodinian cycle in this aspect. We have also analyzed the distribution in deposits of different types and ages of those light and heavy REE that are the most valuable on the world market. Deposits with a pronounced specialization in different groups of such REE have been identified. They occur in the sampling lists of deposits of all supercontinent cycles, except the Kenoran. [ABSTRACT FROM AUTHOR]

[Display omitted] • Peaks in orogen frequency correspond to supercontinent assembly or breakup. • In the last 2 Gyr angular plate speeds have not changed. • 400-Myr and 90-Myr mantle cycles are well established. Of nine large age peaks in zircon and LIP time series <2300 Ma (2150, 1850, 1450, 1400, 1050, 800, 600, 250 and 100 Ma), only four are geographically widespread (1850, 1400, 800 and 250 Ma). These peaks occur both before and after the onset of the supercontinent cycle, and during both assembly and breakup phases of supercontinents. During supercontinent breakup, LIP activity is followed by ocean-basin opening in some areas, but not in other areas. This suggests that mantle plumes are not necessary for ocean-basin opening, and that LIPs should not be used to predict the timing and location of supercontinent breakups. LIP events may be produced directly by mantle plumes or indirectly from subduction regimes that have inherited mantle-cycle signatures from plume activity. A combination of variable plume event intensity and multiple plume cyclicities best explains differences in LIP age peak amplitudes and irregularities. Peaks in orogen frequency at 1850, 1050, 600 Ma, which approximately coincide with major zircon and LIP age peaks, correspond to onsets of supercontinent assembly, and age peaks at 1450, 250 and 100 Ma correspond to supercontinent stasis or breakup. Although collisional orogens are more frequent during supercontinent assemblies, accretionary orogens have no preference for either breakup or assembly phases of supercontinents. A sparsity of orogens during Rodinia assembly may be related to incomplete breakup of Nuna as well as to the fact that some continental cratons never accreted to Rodinia. There are three groups of passive margins, each group showing a decrease in duration with time: Group 1 with onsets at 2.2–2.0 Ga correspond to the breakup of Neoarchean supercratons; Group 2 with onsets at 1.5–1.2 Ga correspond to the breakup of Nuna; and Group 3 with onsets at 1.5–0.1 Ga not corresponding to any particular supercontinent breakup. New paleogeographic reconstructions of supercontinents indicate that in the last 2 Gyr average angular plate speeds have not changed or have decreased with time, whereas the number of orogens has increased. A possible explanation for decreasing or steady plate speed is an increasing proportion of continental crust on plates as juvenile continental crust continued to be added in post-Archean accretionary orogens. Cycles of mantle events are now well established at 90 and 400 Myr. Significant age peaks in orogen frequency, average plate speed, LIPs and detrital zircons may be part of a 400-Myr mantle cycle, and major age peaks in the cycle occur near the onset of supercontinent assemblies. The 400-Myr cycle may have begun with a "big bang" at the 2700 Ma, although the LIP age spectrum suggests the cycle may go back to at least 3850 Ma. Large age peaks at 1850, 1050, 600 and 250 Ma may be related to slab avalanches from the mantle transition zone that occur in response to supercontinent breakups. [ABSTRACT FROM AUTHOR]

The geodynamic process from the evolution of supercontinent has distinct isotope characteristics explorable using zircon Hf isotopic composition. Since Peninsular Malaysia associates with Gondwana dispersal and Pangaea formation, analyzing the U-Pb and Hf-isotopic content of its 500–200 Ma magmatic zircon could reveal the signal left by the transitional geodynamic process between the supercontinents. We collected two groups of magmatic rocks from West Malaya: Ordovician meta-volcanics (n = 8), and Triassic Main Range granitoid province (MRGP) (n = 6); and three groups from East Malaya: Carboniferous meta-volcanics (n = 2), Permian-Triassic Eastern granite province (EGP) (n = 6), and Permian-Triassic EGP volcanics (n = 8). Difference in magmatic zircon Hf isotopic crustal model ages uphold the previous rationale which separates Peninsular into two blocks: West Malaya (part of Sibumasu terrane) magmatic zircon Hf isotopic crustal model ages (Average T DM2 : 1.3 Ga) are older than East Malaya (part of Chanthaburi-Sukhothai-Lincang arc of Indochina terrane) (Average T DM2 : 0.9 Ga). During the final assembly of Gondwana from 500 to 450 Ma, West Malaya and East Malaya were at the outboard of Gondwana Proto-Tethys margin. The shift of East Malaya zircon Hf array towards higher ε Hf (t) (external orogenic system) after ca.370 Ma may infers Paleo-Tethys ocean broadening and East Malaya separation from Gondwana. The 370–350 Ma juvenile zircon Hf isotopic composition in East Malaya is a significant improvement over radiolarian age to show the broadening and subduction of the Paleo-Tethys ocean between the two terranes. After ca.280 Ma, East Malaya zircon Hf array shifted towards lower ε Hf (t) (internal orogenic system). Coinciding with the Indosinian collision at ca.230 Ma, crustal reworking signal increases in both blocks, signifying the end in Peninsular Malaysia Gondwana to Pangaea transitional geodynamic process. As the Paleo-Tethys segment was completely subducted after 230 Ma, the peninsular crustal thickening starts from 230 to 218 Ma. The post-collision phase would begin at ca.215 Ma. [Display omitted] • West Malaya magmatic zircon Hf crustal model ages are older than East Malaya. • East Malaya zircon higher ε Hf (t) after ca. 370 Ma infers Paleo-Tethys broadening • Peninsular Malaysia transitional geodynamic process to Pangaea finished ca. 230 Ma [ABSTRACT FROM AUTHOR]

AbstractThe relationships between plate motions and basal mantle structure remain poorly understood, with some models implying that the basal mantle structure has remained stable over time, while others suggest that it could be shaped by the aggregation and dispersal of supercontinents. Here we investigate the evolution of mantle flow driven by end‐member plate tectonic models over 1 Gyr. We implement a tectonic scenario in which supercontinent reassembly occurs by introversion, and consider three distinct references frames that result in different net lithospheric rotation. Our flow models predict a dominant degree‐2 mantle structure most of the time. We analyze the relationship between imposed tectonic velocities and deep mantle flow, and find that at spherical harmonic degree 2, the maxima of lower mantle radial flow and temperature follow the motion path of the maxima of surface divergence. It may take ∼160–240 Myr for lower mantle structure to reflect plate motion changes when the lower mantle is reorganized by slabs sinking onto basal thermochemical structures, and/or when slabs stagnate in the transition zone before sinking to the lower mantle. Basal thermochemical structures move at less than 0.6°/Myr in our models, with a temporal average of 0.16°/Myr when there is no net lithospheric rotation, and between 0.20 and 0.23°/Myr when net lithospheric rotation exists and is induced in the lower mantle. Our results suggest that basal thermochemical structures are not stationary, but rather linked to global plate motions and plate boundary reconfigurations, reflecting the dynamic nature of the coevolving plate‐mantle system.

The relationships between plate motions and basal mantle structure remain poorly understood, with some models implying that the basal mantle structure has remained stable over time, while others suggest that it could be shaped by the aggregation and dispersal of supercontinents. Here we investigate the evolution of mantle flow driven by end‐member plate tectonic models over 1 Gyr. We implement a tectonic scenario in which supercontinent reassembly occurs by introversion, and consider three distinct references frames that result in different net lithospheric rotation. Our flow models predict a dominant degree‐2 mantle structure most of the time. We analyze the relationship between imposed tectonic velocities and deep mantle flow, and find that at spherical harmonic degree 2, the maxima of lower mantle radial flow and temperature follow the motion path of the maxima of surface divergence. It may take ∼160–240 Myr for lower mantle structure to reflect plate motion changes when the lower mantle is reorganized by slabs sinking onto basal thermochemical structures, and/or when slabs stagnate in the transition zone before sinking to the lower mantle. Basal thermochemical structures move at less than 0.6°/Myr in our models, with a temporal average of 0.16°/Myr when there is no net lithospheric rotation, and between 0.20 and 0.23°/Myr when net lithospheric rotation exists and is induced in the lower mantle. Our results suggest that basal thermochemical structures are not stationary, but rather linked to global plate motions and plate boundary reconfigurations, reflecting the dynamic nature of the coevolving plate‐mantle system. Plain Language Summary: Plate tectonic theory, underpinned by a multitude of observations, requires that the tectonic plates and the mantle coevolve. However, whether the lowermost part of the mantle is involved in this evolution, and its relationship with surface plate motions, is poorly known. We build end‐member absolute plate motions models extending back to 1 billion years, and then model mantle convection using time‐dependent surface velocities from plate tectonic models as a boundary condition. We find that the long‐wavelength lower mantle radial flow field and temperature field follow the motion path of the long‐wavelength surface divergence. It may take ∼160–240 Myr for the lower mantle structure to reflect major plate motion changes and plate boundary reconfigurations when the lower mantle is reorganized by sinking slabs sinking onto basal mantle structures, and/or when slabs stagnate in the mantle transition zone (∼410–660 km) before sinking to the lower mantle due to the larger viscosity of lower mantle. Our results suggest that the basal mantle is not stationary, but rather evolves driven by surface plate motions, indicating that the lithosphere and the entire mantle constitute a coevolving dynamic system. Key Points: Our reconstructions of the plate‐mantle system back to 1 Ga show that deep mantle structures are mobile and shaped by plate motionsIt may take ∼160–240 Myr for deep mantle structure to reflect major changes in plate boundary configurationsIn the presence of continents, the deep mantle structure is dominantly degree‐2 [ABSTRACT FROM AUTHOR]

The distributions of niobium mineral deposits and their resources on the geological time scale are analyzed. The sampling list includes 45 mineral deposits with their individual resources estimated not less than 105 tons of Nb2О5. The classification of deposits used includes three types, namely, alkaligranitic, foidic, and carbonatitic. The geohistorical variability in niobium metallogeny is presented through comparison of supercontinent cycles. To date, no deposits belonging to the Kenoran cycle, which are of interest for the targeted extraction of niobium, have been identified. The Columbian cycle is the oldest among the significant cycles in niobium metallogeny, but its resources are relatively small. The most significant resources of niobium are related to alkaline igneous complexes of the Rodinian, Pangean, and Amasian cycles. The resources of carbonatitic deposits are sharply predominant among all resources generated in the cycles of geological history considered. A consistent increase in the share of resources of such deposits is established through the chronological sequence of supercontinent cycles. The maximum amount of resources of the foidic type is concentrated in the deposits of the Rodinian cycle, while a much smaller amount is in those of the Columbian and Pangean cycles, and no foidic deposits have been identified in the Amasian cycle. The alkaligranitic type demonstrates the smallest fluctuations in niobium resources among the cycles compared; however, its relative contribution to the total resources of all cycles is very small, except for the low-productive Columbian cycle. Despite the close relationships between niobium and tantalum in the mineral-forming processes, these elements do not always show mutually comparable ore concentrations in terms of economic value in the same deposits. Such a coincidence chiefly takes place in mineral deposits of the foidic and alkaligranitic types, which are not yet of great importance in real extraction of both niobium and tantalum. In terms of economic value, carbonatites are almost always specialized exclusively in niobium, while rare-metal pegmatites and granites are specialized in tantalum. These types of mineral deposits are formed in completely different geodynamic environments from magmas of contrasting composition that originated in different lithospheric layers. Therefore, the revealed differences in the historical metallogeny of these two metals have a logical explanation. [ABSTRACT FROM AUTHOR]

Hafnium isotopes of zircon represent a well-dated proxy for the evolution of magmatic systems through Earth history. Time series analysis on the hafnium isotopes of zircon reveals a hierarchy of statistically significant periodic signals spanning multiple orders of magnitude (106–109 year cycles). We attribute the hierarchy of cyclicity to organizing mechanisms of mantle and lithospheric convection at various time scales, ranging from short-term cycles in magmatism and subduction to long-term cycles related to oceans, supercontinents, and superoceans. A ∼600-Myr supercontinent cycle is the strongest signal in the global hafnium database and the phase relationship implies elevated mantle-derived magmatism during supercontinent tenure and elevated crustal reworking during plate reorganization, as expected. A half-supercontinent cycle (Wilson cycle) and a double-supercontinent cycle (superocean cycle) are also present, harmonic with the supercontinent cycle, and related to each other by amplitude modulation. Analysis of local magmatic systems of the circum-Pacific subduction girdle surrounding Pangaea reveal similar significant and harmonic cycles of ∼6 and ∼20 Myr attributed to magmatic cycles and ∼60, ∼120, and ∼240 Myr attributed to subduction cycles. All subduction systems reveal a prevalent ∼60 Myr cycle attributed to an upper mantle convective cycle that has two phase relationships, suggesting that advancing and retreating arc systems can be identified with time series analysis. The harmonic hierarchy of geodynamic cycles identified herein controlled by mantle convection on long time scales and lithospheric convection on short time scales arguably completes the picture of cyclicity in the Earth system, complimenting well-known orbital, oceanic, and astronomical cycles. Unlabelled Image • Hafnium isotopes in zircon provide a proxy to track magmatic systems through time. • Time series analysis of zircon Hf shows cycles with periodicities of Myr to Gyr. • Cycles correspond to magmatic, subduction, Wilson, supercontinent, and superocean cycles. [ABSTRACT FROM AUTHOR]

The global distribution of tantalum deposits and their resources on the geological time scale is analyzed. The analysis is based on the data for 65 deposits of the world with a resource estimate from 2000 t of Ta2O5, which are classified into five types: pegmatitic, granitic, alkaligranitic, foidic, and carbonatitic. Placers and ore-bearing weathering crusts are taken into account with their bedrock sources. The variable features of the global metallogeny of tantalum are represented based on the comparison of the supercontinent cycle. It is established that the most significant resources in terms of quantity are confined in the deposits of the Rodinian cycle, among which the foidic type objects are fully dominant. Then, the descending order for the total resources is the Pangean and Columbian cycles, in which the main shares in the resources belong to the deposits of the alkaligranitic and foidic types. The Kenoran cycle, which lags behind them in its quantitative estimate, stands out in tantalum metallogeny by a monotype nature: only pegmatitic objects have created its resource potential. The current Amasian cycle is in the last place with respect to the total quantity of tantalum resources, which is explained to a great extent by its incompleteness. The resources of this cycle are distributed between the objects of the alkaligranitic, granitic, and pegmatitic types in comparable shares. It is noted that, due to their mineralogical features, the deposits of pegmatitic and granitic types make it possible to obtain the highest-quality concentrates and they are, therefore, of prime interest for tantalum extraction. The deposits of the pegmatitic types are known in all the cycles, while the deposits of the granitic type are known only in the Pangean and Amasian cycles. In total, they contain only one fifth of the estimated tantalum resources, and their major share accounts for the Kenoran and Pangean cycles. [ABSTRACT FROM AUTHOR]

First‐order variations in sea level exhibit amplitudes of ∼200 m over periods that coincide with those of supercontinental cycles (∼300–500 Myr). Proposed mechanisms for this sea level change include processes that change the container volume of the ocean basins and the relative elevation of continents. Here we investigate how unbalanced rates of water exchange between Earth's surface and mantle interior, resulting from fluctuations in tectonic rates, can cause sea level changes. Previous modeling studies of subduction water fluxes suggest that the amount of water that reaches sub‐arc depths is well correlated with the velocity and age of the subducting plate. We use these models to calibrate a parameterization of the deep subduction water flux, which we together with a parameterization of mid‐ocean ridge outgassing, then apply to reconstructions of Earth's tectonic history. This allows us to estimate the global water fluxes between the oceans and mantle for the past 230 Myr and compute the associated sea level change. Our model suggests that a sea level drop of up to 130 m is possible over this period and that it was partly caused by the ∼150Ma rift pulse that opened the Atlantic and forced rapid subduction of old oceanic lithosphere. This indicates that deep water cycling may be one of the more important sea level changing mechanisms on supercontinental time scales and provides a more complete picture of the dynamic interplay between tectonics and sea level change. Key Points: An imbalance between water fluxes into the mantle at trenches and out of the mantle at ridges may have changed sea level since Pangea timeWe estimate ocean mass change from tectonic reconstructions using parameterizations of subduction water flux based on slab age and velocityFaster slabs during Pangea breakup transported extra water to the mantle, contributing to a sea level drop of up to ∼130 m since 230 Ma [ABSTRACT FROM AUTHOR]

Abstract The extent of continental rifts and subduction zones through deep geological time provides insights into the mechanisms behind supercontinent cycles and the long term evolution of the mantle. However, previous compilations have stopped short of mapping the locations of rifts and subduction zones continuously since the Neoproterozoic and within a self-consistent plate kinematic framework. Using recently published plate models with continuously closing boundaries for the Neoproterozoic and Phanerozoic, we estimate how rift and peri-continental subduction length vary from 1 Ga to present and test hypotheses pertaining to the supercontinent cycle and supercontinent breakup. We extract measures of continental perimeter-to-area ratio as a proxy for the existence of a supercontinent, where during times of supercontinent existence the perimeter-to-area ratio should be low, and during assembly and dispersal it should be high. The amalgamation of Gondwana is clearly represented by changes in the length of peri-continental subduction and the breakup of Rodinia and Pangea by changes in rift lengths. The assembly of Pangea is not clearly defined using plate boundary lengths, likely because its formation resulted from the collision of only two large continents. Instead the assembly of Gondwana (ca. 520 Ma) marks the most prominent change in arc length and perimeter-to-area ratio during the last billion years suggesting that Gondwana during the Early Palaeozoic could explicitly be considered part of a Phanerozoic supercontinent. Consequently, the traditional understanding of the supercontinent cycle, in terms of supercontinent existence for short periods of time before dispersal and re-accretion, may be inadequate to fully describe the cycle. Instead, either a two-stage supercontinent cycle could be a more appropriate concept, or alternatively the time period of 1 to 0 Ga has to be considered as being dominated by supercontinent existence, with brief periods of dispersal and amalgamation. Highlights • Compilation of rifting events in the Neoproterozoic • Analysis of continental arc, continental rift and connectedness of continental lithosphere for the last 1 Ga • Two stage supercontinent cycle may better explain changes in the connectedness of continental lithosphere • Extraversion and introversion models of successive supercontinents occur on different timescales [ABSTRACT FROM AUTHOR]

Abstract: Accessing the cyclicity and persistence of geological records with time series analysis deepens our understanding of Earth's long‐term evolution. In this study, time series from recent global zircon U‐Pb age and δ18O databases are analyzed using wavelet transform from a fractal perspective. Continuous wavelet transform of the local fractal sequences of both zircon records indicates a strong, persistent ~760 million year cycle over the 4.4 billion years of Earth's history. Wavelet coherence analysis shows that the U‐Pb age and δ18O systems are coupled in significant in‐phase coherence for a cycle of ~760 million year, implying synchronization between the two underlying processes. This study also demonstrates that the variation in the time series records manifests as 1/f β scaling behavior that persists β ~ 1.8 over the entire interval. This 1/f fractal scaling nature furnishes evidence for the conjecture that rather than being an equilibrium system, Earth's long‐term evolution follows a self‐organized pattern. [ABSTRACT FROM AUTHOR]

Certain hard and normally opaque minerals, both rare and common, occasionally crystallize as transparent or partly transparent ‘gem’ crystals. Such stones, designated ‘crystalline coloured gemstones’ (CCGs), form under highly constrained just-so ‘Goldilocks’ conditions that did not exist prior to the last supercontinent cycle. One set of gem-forming conditions arises during continent-to-continent collisions. Another comes into existence during the breakup of continents and produces distinctively different gems. Over 50 different CCG-forming metamorphic and pegmatitic minerals of the first type crystallize in certain orogenic areas near the edges of continents. In East Africa, the Himalayas, Pamirs and Hindu Kush, groups of CCG deposits formed near the leading edge of the upper plate during the collisions, and are associated with large scale circular arcs. Gems of the second type, which are for the most part blue-green-yellow magmatic sapphires, occur in conjunction with continental volcanism in eastern Australia, far eastern Russia, eastern China, Laos, Vietnam, Thailand, Rwanda, Cameroon, Nigeria and elsewhere. Orogeny causes deep fractures to be regenerated upward into younger rocks. CCG deposits of the first type are systematically associated with ancient fractures originating from below, vestiges of the Earth’s early history. Fractures may be older than the rocks in which they are observed. [ABSTRACT FROM AUTHOR]

Earth is 180 Myr into the current supercontinent cycle, and the next supercontinent is predicted to form in 250 Myr. The continuous changes in continental configuration can move the ocean between resonant states, and the semidiurnal tides are currently large compared to the past 252 Myr due to tidal resonance in the Atlantic. This leads to the hypothesis that there is a “supertidal” cycle linked to the supercontinent cycle. Here this is tested using new tectonic predictions for the next 250 Myr as bathymetry in a numerical tidal model. The simulations support the following hypothesis: a new tidal resonance will appear 150 Myr from now, followed by a decreasing tide as the supercontinent forms 100 Myr later. This affects the dissipation of tidal energy in the oceans, with consequences for the evolution of the Earth-Moon system, ocean circulation and climate, and implications for the ocean’s capacity of hosting and evolving life. [ABSTRACT FROM AUTHOR]

The Meghalaya Plateau and the Mikir Hills constitute a northeastern extension of the Precambrian Indian Shield. They are dominantly composed of Proterozoic basement granite gneisses, granites, migmatites, granulites, the Shillong Group metasedimentary cover sequence, and Mesozoic-Tertiary igneous and sedimentary rocks. Medium to coarse grained, equigranular to porphyritic Cambrian granite plutons intrude the basement granite gneisses and the Shillong Group. U-Pb SHRIMP zircon geochronology and geochemistry of the granite gneisses and granites have been carried out in order to understand the nature and timing of granite magmatism, supercontinent cycles, and crustal growth of the Meghalaya Plateau and Mikir Hills. Zircons from the Rongjeng granite gneiss record the oldest magmatism at 1778 ± 37 Ma. An inherited zircon core has an age of 2566.4 ± 26.9 Ma, indicating the presence of recycled Neoarchaean crust in the basement granite gneisses. Zircons from the Sonsak granite have two ages: 523.4 ± 7.9 Ma and 1620.8 ± 9.2 Ma, which indicate partial assimilation of an older granite gneiss by a younger granite melt. Zircons from the Longavalli granite gneiss of the Mikir Hills has a crystallization age of 1430.4 ± 9.6 Ma and a metamorphic age of 514 ± 18.6 Ma. An inherited core of a zircon from Longavalli granite gneiss has an age of 1617.1 ± 14.5 Ma. Zircons from younger granite plutons have Cambrian mean ages of 528.7 ± 5.5 Ma (Kaziranga), 516 ± 9.0 Ma (South Khasi), 512.5 ± 8.7 Ma (Kyrdem), and 506.7 ± 7.1 Ma and 535 ± 11 Ma (Nongpoh). These plutons are products of the global Pan-African tectonothermal event, and their formation markedly coincides with the later stages of East Gondwana assembly (570–500 Ma, Kuunga orogen). The older inherited zircon cores (2566.4 ± 26.9 Ma, 1758.1 ± 54.3 Ma, 1617.1 ± 14 Ma) imply a significant role for recycled ancient crust in the generation of Cambrian granites. Thus the Meghalaya Plateau and Mikir Hills experienced major felsic magmatic episodes at ~ 1800 Ma, ~ 1600 Ma, ~ 1400 Ma, and ~ 500 Ma with recycling of Neoarchaean crust, and later contributions from Paleo-Mesoproterozoic granite gneiss sources. A 258 ± 20 Ma lower intercept age of the Rongjeng granite gneiss perhaps indicates a Permo-Triassic thermal imprint on the Meghalaya Plateau. The granite gneisses and granites have peraluminous to metaluminous compositions, and syn-orogenic to post-collisional affinities. We conclude that the orogenic history of the Meghalaya Plateau and the Mikir Hills records crustal growth of the Columbia and Gondwana supercontinents as noted in other Pan-African-Indian-Prydz-Brasiliano orogens. [ABSTRACT FROM AUTHOR]

The 176 Lu– 176 Hf radioactive decay system has been widely used to study planetary crust–mantle differentiation. Of considerable utility in this regard is zircon, a resistant mineral that can be precisely dated by the U–Pb chronometer and record its initial Hf isotope composition due to having low Lu/Hf. Here we review zircon U–Pb age and Hf isotopic data mainly obtained over the last two decades and discuss their contributions to our current understanding of crust–mantle evolution, with emphasis on the Lu–Hf isotope composition of the bulk silicate Earth (BSE), early differentiation of the silicate Earth, and the evolution of the continental crust over geologic history. Meteorite zircon encapsulates the most primitive Hf isotope composition of our solar system, which was used to identify chondritic meteorites best representative of the BSE ( 176 Hf/ 177 Hf = 0.282793 ± 0.000011; 176 Lu/ 177 Hf = 0.0338 ± 0.0001). Hadean–Eoarchean detrital zircons yield highly unradiogenic Hf isotope compositions relative to the BSE, providing evidence for the development of a geochemically enriched silicate reservoir as early as 4.5 Ga. By combining the Hf and O isotope systematics, we propose that the early enriched silicate reservoir has resided at depth within the Earth rather than near the surface and may represent a fractionated residuum of a magma ocean underlying the proto-crust, like urKREEP beneath the anorthositic crust on the Moon. Detrital zircons from world major rivers potentially provide the most robust Hf isotope record of the preserved granitoid crust on a continental scale, whereas mafic rocks with various emplacement ages offer an opportunity to trace the Hf isotope evolution of juvenile continental crust (from εHf [4.5 Ga] = 0 to εHf [present] = + 13). The river zircon data as compared to the juvenile crust composition highlight that the supercontinent cycle has controlled the evolution of the continental crust by regulating the rates of crustal generation and intra-crustal reworking processes and the preservation potential of granitoid crust. We use the data to explore the timing of generation of the preserved continental crust. Taking into account the crustal residence times of continental crust recycled back into the mantle, we further propose a model of net continental growth that stable continental crust was firstly established in the Paleo- and Mesoarchean and significantly grew in the Paleoproterozoic. [ABSTRACT FROM AUTHOR]

This study reports the Sr-Nd isotopic composition of Indian shale samples of Archean to Recent age from different litho-units of Archean cratons and Proterozoic basins. Combining our measured Sr-Nd isotopic ratios with literature data, we calculated the Nd model ages of these shales and estimated the growth rate of the Indian continental crust, assuming that the Nd model age of clastic sediments represents an average of existing continental crustal sources. Unlike the widely variable 87Sr/86Sr ratio (0.76 ± 0.12, 1 S.d) and 87Rb/86Sr (2.53 ± 1.09) in the Indian shales, the average present-day 143Nd/144Nd (0.51170 ± 0.00028; ε Nd(0) = −18.8 ± 5.4) and 147Sm/144Nd (0.111 ± 0.009) isotopic ratios of Indian shales (n = 54) estimated in this study are comparable to that of the average global clastic sediments (mostly shales), North American shales, and Ganga River sediments. However, the Nd isotopic compositions of these shales (ε Nd(0) ≈ −19) are slightly different from those of the Upper Continental Crust (UCC), loess, and average river/aeolian particulates (ε Nd(0) ≈ −10), despite having similar Sm/Nd ratios (0.17−0.19). The striking uniformity of Sm/Nd ratios and 143Nd/144Nd in contemporary UCC-derived erosional products like the Ganga River sediments suggests that the isotopic compositions of average Indian shale might be representative of Indian UCC. Using a dimensionless erosional parameter K , the growth of the Indian shield was modeled considering the effect of preferential erosion, which leads to less contribution from older shield areas. We thus develop a two-stage crustal growth model that assumes K = 1 for the Archean (no erosion) and K = 6 for the post-Archean to Recent. Our results suggest that ∼80% of the continental crust was formed by the end of Archean with the mean age of the continent of 2.42 Ga, which is different from the Australian shield. This study represents a first-ever estimate of the growth rate of the Indian shield that manifests a rapid growth in the Archean and a long-term, slow and progressive growth in the post-Archean comprising short periods of rapid crustal growth, which could be correlated with the supercontinent cycle and mantle plume activities forming large igneous provinces (LIPs). • Average 143Nd/144Nd and Sm/Nd ratios of shales are representative of Indian crust. • Depleted mantle Nd model ages of shales constrain the growth of the Indian shield. • ∼80% of the crust formed by the end of Archean, with mean age of continent ∼2.4 Ga. • Growth of continental crust correlates with supercontinent cycles and plume activity. [ABSTRACT FROM AUTHOR]

The balance between constructive versus destructive processes in the formation and recycling of continental crust over Earth history – or crustal growth – remains contentious; whereas some advocate continuous continental growth, others suggest episodic growth predominantly during periods of supercontinent assembly. In this paper, we review the geological record and present an analysis of time constrained hafnium and oxygen isotopes in dated zircon crystals, and of incompatible elements (Zr, Th) in dated magmatic rocks, to explore the operation of Earth's supercontinent cycle. This analysis reveals the importance of the supercontinent cycle to continental growth by demonstrating a link between periods of enhanced crustal recycling and elevated geochemical proxies of subduction flux. The temporal fluxes in subduction rate suggest a conditioned duality of the Earth system between alternating periods of hot, volatile-rich, and cold, volatile-depleted, mantle relative to an idealised power decrease curve. Hot, volatile-rich mantle periods accompany supercontinent dispersion events and are characterised by mantle superplumes and increased crustal recycling during rapid global subduction. Cool, volatile-depleted mantle periods that accompany aggregated supercontinents are interpreted to arise from a combination of the widespread subduction of cold oceanic lithosphere, volatile depletion arising from the preceding voluminous subduction-related magmatism, and core insulation by the slab graveyards that accompanied formation of the supercontinent: these periods are characterised by enhanced mantle influence on magmas but low rates of continental crust production. Pulses of rapid continental growth that accompanied supercontinent assembly led to crustal oversteps — which can be considered as periods when too much crust had formed relative to the thermal state of the mantle at that time. When combined with the anomalous mantle cooling that accompanied these pulses of rapid crust formation, we postulate that supercontinent assembly led to a stepwise increase in plate size via changes in tessellation during supercontinent dispersal. [ABSTRACT FROM AUTHOR]

The formation and destruction of supercontinents requires prolonged convergent tectonics between particular plates, followed by intra-continental extension during subsequent breakup stages. A specific feature of the Late Paleozoic supercontinent Pangea is the prolonged and diachronous formation of the collisional belts of the Rheic suture zone coeval with recurrent continental breakup and subsequent formation of the mid-ocean ridge systems of the Paleo- and Neo-Tethys oceans at the Devonian and Permian margins of the Gondwana plate, respectively. To decide whether these processes are causally related or not, it is necessary to accurately reconstruct the plate motion of Gondwana relative to Laurussia. Here we propose that the strain pattern preserved in the continental crust can be used for the reconstruction of ancient plate kinematics. We present Euler pole locations for the three fundamental stages of the Late Paleozoic assembly of Pangea and closure of the Rheic Ocean: (I) Early Devonian (ca. 400 Ma) collisional tectonics affected Gondwana at the Armorican Spur north of western Africa and at the promontory of the South China block/Australia of eastern Gondwana, resulting in the Variscan and the Qinling orogenies, respectively. The Euler pole of the rotational axis between Gondwana and Laurussia is positioned east of Gondwana close to Australia. (II) Continued subduction of the western Rheic Ocean initiates the clockwise rotation of Gondwana that is responsible for the separation of the South China block from Gondwana and the opening of Paleo-Tethys during the Late Devonian. The position of the rotational axis north of Africa reveals a shift of the Euler pole to the west. (III) The terminal closure of the Rheic Ocean resulted in the final tectonics of the Alleghanides, the Mauritanides and the Ouachita–Sonora–Marathon belt, occurred after the cessation of the Variscan orogeny in Central Europe, and is coeval with the formation of the Central European Extensional Province and the opening of Neo-Tethys at ca. 300 Ma. The Euler pole for the final closure of the Rheic Ocean is positioned near Oslo (Laurussia). Thus, the concomitant formation of convergent and divergent plate boundaries during the assembly of Pangea is due to the relocation of the particular rotational axis. From a geodynamic point of view, coupled collisional (western Pangea) and extensional tectonics (eastern Pangea) due to plate tectonic reorganization is fully explained by slab pull and ridge push forces. [ABSTRACT FROM AUTHOR]