Supercontinent Assembly Research Articles

Precambrian Tectonic Evolution of Southern Kongling Terrane, Yangtze Craton: Constraint From the Detrital Zircon U‐Pb Geochronology of the Metasedimentary Rocks

AbstractThe Kongling terrane (Huangling dome) outcrops Precambrian metamorphic basement of the Yangtze craton. However, the Precambrian tectonic evolution of the southern Kongling terrane remains poorly constrained. In this contribution, we report zircon geochronology of the metasedimentary rocks from southern Kongling terrane of the Yangtze craton. Zircon U‐Pb dating results yielded magmatic age clusters at ca. 3,000 Ma, ca. 1,520 Ma, ca. 1,150 Ma, ca. 860 Ma, 900–920 Ma, and 980 Ma, and metamorphic age at ca. 2,900 Ma. These data display that the southern Kongling terrane witnessed Mesoarchean magmatism and metamorphic event, Mesoproterozoic and Neoproterozoic magmatism. In combination with previous studies, it is proposed that the Precambrian metamorphic basement of the Yangtze craton was amalgamated by the multi‐stage subduction‐collision processes at ca. 3,000–2,900 Ma, ca. 2,000–1,800 Ma, and ca. 1,100–940 Ma. In addition, the Proterozoic processes were related to the assembly and breakup of Columbia and Rodinia supercontinents.

Lithospheric architecture below the Eastern Ghats Mobile Belt and adjoining Archean cratons: Imprints of India-Antarctica collision tectonics

The investigation of the rigid lithospheric mantle architecture floating over the weaker hotter asthenosphere is key to understanding the plate tectonic evolution of the Eastern Ghats Mobile Belt and the adjoining Archean cratons. We present shear-wave velocity (VS) structure for the crust and upper-mantle below the Eastern Ghats Mobile Belt (EGMB) and adjacent Archean cratons. The lithospheric structure is constrained through 4–150 s fundamental-mode Rayleigh and Love-wave group velocity dispersion measurements, using regional (2°–30°) earthquakes recorded at 27 seismic stations installed along two distinct profiles. Velocity models are improved by joint inversion of resultant dispersion curves with receiver functions computed from the teleseismic P-waves. Observed variations in crustal and lithospheric architecture across the domains of the Eastern Ghats Province are implication of the deformations due to rifting and collision of India and East Antarctica in the context of assembly and breakup of Rodinia and Gondwana supercontinents. The cratons and the mobile belt are characterised by 34–38 km, ∼45 km thick heterogeneous crust and 120–160 km, 90–120 km thick lithospheres, respectively. The abrupt changes in the crustal thickness owes its origin to the collisional thrusting of the Eastern Ghats Province against the Archean cratons. Significant variations in the nature of Moho are also noted. The flat sharp cratonic Moho is distinct from the gradational Moho below the Eastern Ghats Province, possibly a signature of magmatic underplating below the mobile belt. The nature of the lithosphere-asthenosphere boundary (LAB) interpreted from the gradient change in velocity appears to be poorly-resolved. Therefore, we utilise radial anisotropy determined from the discrepancy between VSH and VSV based on Rayleigh and Love-wave velocities respectively, as a proxy. Our findings confirm the LAB through positive radial anisotropy (VSH > VSV) prevalent in the asthenospheric-mantle that is likely explained by flow-induced shear. Overall, the lithospheric architecture below the study area has been shaped through several deformational episodes that distinguish the multiple litho-tectonic units within the mobile belt. The loss of cratonic lithospheric keel can be attributed to the mantle plume given the Gondwanan trajectory of the Indian subcontinent over Kerguelen and Crozet hotspots.

The onset timing of plate tectonics: Controversies,progress, and prospects

<p indent="0mm">Plate tectonics is widely accepted as a fundamental theory in Earth science and is hailed as an important scientific discovery of the 20th century. However, the major challenge of this theory since its foundation for half a century now is the debate over when Earth first developed plate tectonics—4 billion years ago vs. later than 1 billion years ago—an uncertainty which spans nearly three-quarters of Earth history. At present, most researchers view the “earliest evidence of subduction” as the timing of onset of plate tectonics. However, it is debated which phenomena could be viewed as the “oldest evidence”. In this study, we argued that local subduction itself cannot be equated with plate tectonics, but rather, a global subduction network is the essence of plate tectonics. We first conducted comprehensive geological observations along the northern margin of the North China Craton. We recognized key information supporting significant horizontal movement and subduction of an oceanic plate at a convergent tectonic boundary nearly 2 billion years ago, and reconstructed the accurate position of North China in the Earth’s first supercontinent based on its iconic subduction record. According to the prediction of the new proposed geological model, there should be a relic of a subduction interface preserved beneath the North China Craton at the depth of the crust-mantle boundary. We then carried out a high-resolution seismic survey across the northern North China. The seismic profile indeed revealed the geophysical interface preserved by the ancient continental convergence. These features identified are identical to the surface and deep structure of the modern Himalayan orogenic belt, indicating that North China underwent a similar geological process at 2 billion years ago. Because we have assessed the geology and geophysics of the ancient Tethyan Realm, and concluded that subduction has been the main driver of plate motion over the last 500 million years, accordingly, the plate tectonics should work as a subduction network that was driven by subducting plates. Following this knowledge, we finally put the key findings from China in a global context, and proposed that Earth gave birth to its global plate subduction network 2 billion years ago, leading to the formation of Earth’s earliest supercontinent due to the pulling forces of subduction. Therefore, the supercontinent is the result of the global plate subduction network, which can be used as the signpost to identify the onset of plate tectonics. Only after the onset of the global tectonic network did the Earth start the cyclic assembly and breakup of supercontinents. Such active plate margins led to intensive mass and energy exchange between Earth’s surface and interior, which was an important driving force for maintaining and even enhancing planetary habitability. The onset of plate tectonics signifies the contrasting evolutionary paths among Earth and other planets. Future research involves quantitative analysis on why the plates can be subducted continuously. Innovative systems of data- and model-driven scientific research can help us better understand the Earth’s past and consequently predict its future.

The Neoarchean and Paleoproterozoic crustal evolution of the Clearwater block, northwestern Laurentia: Implications for the assembly of supercontinents

We report new coupled zircon U-Pb age and Hf isotope data, along with whole-rock Hf-Nd isotope data for 20 samples from the Priest River and Clearwater complexes—Neoarchean and Paleoproterozoic basement exposures in northern Idaho, northwest Laurentia. The new zircon data reveal two well-defined periods of magmatism at ∼ 2.66 and ∼ 1.86 Ga in each complex, with no evidence of any intervening or older magmatic events. Positive zircon initial εHf values of the Neoarchean rocks (+1 to +3) indicate juvenile magmas derived from a depleted mantle source. The Paleoproterozoic rocks, in both complexes, share a much wider range of initial zircon εHf values (−7 to +6) which suggests magmas derived from a depleted mantle source intruded and assimilated pre-existing Neoarchean continental crust. The shared age and isotope compositions in the Priest River and Clearwater complexes suggest that the two complexes likely belong to a single crustal block—the Clearwater block.Based on these new zircon U-Pb ages and Hf isotopic data of the Neoarchean and Paleoproterozoic rocks, the Clearwater block is shown to be distinct from the nearby Wyoming Province, the Medicine Hat block, and components of the Great Falls tectonic zone. We also report new zircon Hf isotope data for the ∼ 1.58 Ga Laclede orthogneiss in the Clearwater block, which along with published U-Pb and Hf isotope constraints, support a paleogeographic connection between the Gawler craton, East Antarctica, and northwestern Laurentia during ∼ 1.9 Ga to ∼ 1.6 Ga. Comparison with other examples of co-existing Neoarchean and Paleoproterozoic igneous rocks present in other continents suggests that the global record of 2.7–2.5 Ga magmatism often represents new crustal additions from a depleted mantle reservoir. The record of 2.0–1.7 Ga rocks also represent additions of juvenile magma, but with significantly larger contributions from pre-existing continental crust. In many cases the 2.0–1.7 Ga crust preserved on Earth today was added during the assembly of the supercontinent Nuna.

Petrogenesis and Tectonic Implications of the Neoproterozoic Peraluminous Granitic Rocks from the Tianshui Area, Western Margin of the North Qinling Terrane, China: Evidence from Whole-Rock Geochemistry and Zircon U–Pb–Hf–O Isotopes

The source and petrogenesis of peraluminous granitic rocks in orogenic belts can provide insights into the evolution, architecture, and composition of continental crust. Neoproterozoic peraluminous granitic rocks are sporadically exposed in the Tianshui area of the western margin of the North Qinling Terrane (NQT), China. However, the source, petrogenesis, and tectonic setting of these rocks still remain unclear, which limits our understanding of the Precambrian tectonic and crustal evolution of the Qinling Orogenic Belt (QOB). Here, we determined the whole-rock geochemical compositions and in situ zircon U–Pb ages, trace-element contents, and Hf–O isotopic compositions of a series of peraluminous granitic mylonites and granitic gneisses in the Tianshui area at the west end of North Qinling. Zircon U–Pb dating revealed that the protoliths of the studied granitic mylonites and granitic gneisses crystallized at 936–921 Ma. The granitic rocks displayed high A/CNK values (1.12–1.34) and were enriched in large-ion lithophile elements (e.g., Rb, Ba, Th, U, and K) and light rare earth elements, and they were depleted of high-field-strength elements (e.g., Nb, Ta, and Ti). These rocks showed variable zircon εHf(t) (−12.2 / 9.7) and δ18O (3.56‰ / 11.07‰) values, suggesting that they were derived from heterogeneous crustal sources comprising predominantly supracrustal sedimentary rocks and subordinate igneous rocks. In addition, the U–Pb–Hf isotopic compositions from the core domains of inherited zircons were similar to those of detrital zircons from the Qinling Group, suggesting that the Qinling Group was an important crustal source for the granitic rocks. The lithological and geochemical features of these granitic rocks indicate that they were generated by biotite dehydration melting of heterogeneous sources at lower crustal depths. Combining our results with those of previous studies, we suggest that the NQT underwent a tectonic transition from syn-collision to post-collision at 936–874 Ma in response to the assembly and breakup of the Rodinia supercontinent.

The supercontinent cycle and Earth's long-term climate.

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.

Neoproterozoic reworking of a Mesoproterozoic magmatic arc from the north-eastern part of the Central Indian Tectonic Zone: Implication for the growth and disintegration of the Indian shield in the Proterozoic supercontinental cycles

Thermotectonic evolution of the rocks of the Central Indian Tectonic Zone (CITZ) is crucial to understand the growth of the Indian shield and its response to the supercontinental cycles of the Earth. In this study we present field, petrology, geochemistry, in-situ U-Pb zircon and Th-U-total Pb monazite dates from a suite of felsic orthogneisses from the least studied Makrohar Granulite Belt (MKGB) of the CITZ. Petrology and geochemical data identify two rock groups: charnockitic orthogneiss (COG) and garnet orthogneiss (GOG). Geochemical fingerprints suggest that the magmatic protoliths of the gneisses are S-type granitoids, formed in a continental arc setting. In situ U-Pb zircon dates yield the time of arc magmatism at ca. 1400–1350 Ma. This is the first report of mid-Mesoproterozoic arc magmatism in the CITZ. These arc granites were subsequently metamorphosed at granulite facies condition that culminated at ∼800–850 °C, 7–7.5 kbar. A prominent gneissic (migmatitic) fabric was formed with garnet ± orthopyroxene + plagioclase + K-feldspar + quartz as peak metamorphic assemblages. After reaching the recorded P-T maxima, the studied rocks followed a decompression and cooling path to 4 kbar and 500 °C. The inferred clockwise P-T path is consistent with reworking of the Mesoproterozoic arc granites in a continent–continent collisional setting. In-situ Th-U-total Pb monazite and in-situ U-Pb ages of zircon overgrowth constrain the age of deformation and metamorphism in the span of ca. 974–913 Ma. In combination with the published information, the results of this study are consistent with the views that (a) the Indian shield participated as a coherent block in the Columbia supercontinent since ca. 1450 Ma (or before), (b) the ca. 1400–1350 Ma arc magmatism is presumably linked to collapse or closure of a basin (either north or south of the MKGB) in the CITZ in response to the prolonged accretionary phase of the Columbia supercontinent and (c) during the assembly of the Rodinia supercontinent, localized dismembered fragments of the Columbia got re-amalgamated during late Mesoproterozoic to early Neoproterozoic. Archean cratons got fused along the Proterozoic mobile belts (such as Central Indian Tectonic Zone, Eastern Ghats Mobile Belt). Different units within these mobile belts also experienced local compression during this time frame of the Grenvillian orogeny in the Indian subcontinent.

Association of A‐ and I‐type granitoids in the central Aravalli orogen, Rajasthan: Implications for the Neoproterozoic tectonic evolution of north‐west India

We present new mineralogical and geochemical data for the granitoid plutons of the Neoproterozoic Sendra Granitoid Suite, central Aravalli orogen, north‐west India to constrain their petrogenesis and tectonic setting. The granitoids can be classified into two groups: (a) A‐type Chang, Chitar, Borwar, and Seliberi plutons and (b) I‐type Jaitpura pluton. The available geochronological data (zircon U–Pb ages) suggest that all the granitoids are coeval at 990–970 Ma. The granitoids are mostly granite sensu stricto, with subordinate granodiorite and rare tonalite. The rocks are metaluminous to mildly peraluminous and have high total REE abundances. Nevertheless, there are also certain geochemical differences between A‐type and I‐type granitoids. The I‐type granitoids have relatively high Al2O3 and CaO concentrations and show significant fractionation with increasing SiO2. The least fractionated sample contains low abundances of the HFSE and has low Fe‐number and Ga/Al ratios. In contrast, the A‐type granitoids have lower CaO and higher HFSE concentrations, Fe‐number, and Ga/Al ratios. Both A‐type and I‐type granitoids show negative Ba, Sr, Nb, P, Ti, and Eu anomalies, and are characterized by high zircon‐saturation temperatures (801–977°C). The present data suggest that rocks of the Sendra Granitoid Suite were generated predominantly by partial melting of mafic sources at high temperatures and emplaced in a post‐collisional extensional regime. Moreover, our study provides evidence of the preserved post‐collisional extensional magmatism subsequent to the subduction during the assembly of the Rodinia supercontinent, which is otherwise relatively less prevalent over intra‐plate or within‐plate magmatism during this time period.

Geological history and supercontinent cycles of the Arctic

AbstractThe geological history of the Arctic is constrained within the framework of the assembly and breakup of three supercontinents. The first of these was preceded by the crystallization of the oldest dated rocks on Earth and consolidation of the Arctic region’s Archean cratons between 2.82 and 2.54 Ga. Following the emplacement of regional mafic dike swarms between 2.51 and 2.03 Ga, the cratons were amalgamated into the Nuna (Columbia) supercontinent between 2.0 and 1.6 Ga, and the distribution of low-thermalgradient eclogite (indicative of continental subduction) and ophiolite (indicative of obduction of oceanic crust onto a continental margin) suggests that diagnostic plate-tectonic processes were well in place by the early Paleoproterozoic. Basin formation, flood basalts, and dike swarms are features of the partial(?) breakup of Nuna (Columbia) by 1.5–1.27 Ga. The extent to which specific dike swarms led to continental breakup and a rift-to-drift transition remains unclear. Assembly of the second supercontinent (Rodinia, 1.4–0.9 Ga) is recorded by a network of Grenvillian and Sveconorwegian collisional orogenic belts. Prominent features of Rodinia breakup (780–615 Ma) in the Arctic are extensive dike swarms and regional-scale glacial-periglacial deposits associated with the Sturtian (717–661 Ma) and Marinoan (ca. 645 ± 6 to ca. 635 Ma) snowball Earth glaciations. Assembly of the third supercontinent, Pangea, between 600 Ma and ca. 250 Ma, was accomplished through stitching of four orogens in the Arctic (Timan-Varanger, Caledonian, Ellesmerian, and Urals-Taymyr). Pangea breakup (rifting since 250 Ma and oceanic spreading since the Cretaceous) led to the emplacement of Cretaceous and Paleogene flood basalts, new oceanic crust in the Labrador Sea, North Atlantic Ocean, and Arctic Ocean, and orogens characterized by relatively small but far-traveled accreted terranes with provenance in Laurentia, Baltica, and Siberia. Paleogeographic similarities and geological correlations among Laurentia, Baltica, Siberia, and the North China craton suggest that Rodinia formed following incomplete breakup of Nuna (Columbia) and/or by introversion, whereas unique paleogeographic traits for Pangea within the Arctic region point to supercontinent formation by extroversion.

Understanding the Paleoproterozoic Circum-Superior Large Igneous Province constrains the thermal properties of Earth’s mantle through time

Basalts and komatiites in the ∼1880 Ma Paleoproterozoic Circum-Superior Large Igneous Province are associated in space and time with the closure/subduction of the Manikewan ocean and formation of the Trans-Hudson Orogen during the construction of Laurentia and the supercontinent of Nuna/Columbia. In one model, the igneous rocks formed by the melting of ambient mantle during contemporaneous closure of the Manikewan ocean and rifting of the margins of the Superior craton. In another model melting took place in a mantle plume. Resolution to this problem can help in the understanding of the role of LIPS in supercontinent assembly or breakup over the last 2 billion years of Earth history. It can also constrain the thermal properties of ambient mantle and mantle plumes over the last 3.5 billion years. The contrasting hypotheses were tested by petrological modeling of a large database of basalts and komatiites from the Circum-Superior Large Igneous Province. Results reveal limited variability in mantle potential temperature, from 1540 to 1570 °C, over ∼12 to 15 million years in time and over 1500 km in space from the Cape Smith Belt in the north to the Winnipegosis Belt in the southwest. The essential problem with the mantle plume model for the Circum-Superior LIP is that it predicts thermal heterogeneity, in contrast with the evidence presented here; there is no Phanerozoic mantle plume analog. The limited long wavelength variation in TP is characteristic of ambient mantle magmatism, evidence supporting the plate tectonic model for the Circum-Superior LIP. Results are consistent with ambient mantle thermal models characterized by sluggish mantle convection in the past and with a present-day Urey ratio of about 0.38 (Korenaga, J. 2008. Urey ratio and the structure and evolution of Earth's mantle. Rev. Geophys. 46, RG2007). In contrast, most high MgO komatiites in Paleoproterozoic and Archean greenstone belts melted from sources that were ∼100–200 °C higher. This temperature excess is similar to 100–250 °C for most Phanerozoic mantle plumes, demonstrating approximate constancy of thermal properties of mantle plume structures through time.

Geochemical evidence for a widespread Paleoproterozoic continental arc-back-arc magmatism in the Lesser Himalaya during the Columbia supercontinent assembly

The geodynamic evolution of the proto-northern Indian continental margin during Paleoproterozoic is widely debated. The proposed models include (i) a mantle plume triggered rift-related tectonic setting at a passive continental margin and (ii) an Andean type active continental margin. A widespread quasi-continuous belt of Paleoproterozoic (∼1.9–1.8 Ga) granitoids and orthogneisses, as well as mafic volcanic and intrusive rocks intercalated with metasedimentary rocks, occur all along the strike of Lesser Himalaya. A geochemical re-investigation is presented here using the existing geochemical data on mafic volcanic and intrusive rocks from the Lesser Himalayan Sequence of Himachal, Garhwal, and Nepal sectors to address the tectonic affiliation of these rocks and to infer the geodynamic setting of the proto-northern continental margin of the Indian Shield. These mafic magmatic rocks are classified as subalkaline basalt and basaltic andesite with calc-alkaline magmatic affinity to transitional character between calc-alkaline and tholeiites. Broad initial ɛNd range reveals a heterogeneous mantle source developed by mixing between a depleted mantle and a recycled component. Mantle source enrichment of these rocks is attributed to the interaction between the siliceous partial melt from the subducted sediment-laden oceanic crust and the mantle wedge, which is further supported by compositional similarity with experimental hybrid partial melts of eclogite-peridotite reaction. Estimated mantle potential temperature from the composition of these mafic rocks is comparable to that of mid-oceanic ridge basalts and does not invoke a mantle plume in their genesis. Geochemical proxies based on the major oxide abundances reveal the generation of these rocks from olivine-poor lithologies. It is suggested that these rocks were generated in a back-arc setting during the assembly of the Columbia supercontinent at the proto-northern continental margin of the Indian Shield. Distinct Nd isotopic systematics in these rocks compared to the Paleoproterozoic metamafic rocks of Cathaysia Block of South China Craton questions their purported linkage in the Columbia configuration.

Earth's oldest hotspot track at ca. 1.8 Ga advected by a global subduction system

The concurrence of both global orogenesis and large igneous provinces (LIPs) from 2200–1600 Ma remains enigmatic. This apparent contradiction of top-down and bottom-up geodynamics occurred during assembly of Earth's oldest-known supercontinent. We present a multidisciplinary study combining the dismembered portions of major LIP worldwide and correlate them across supercontinent Columbia to the same plume center (Xiong'er of the North China craton). The succession of LIPs is then used to trace the oldest established hotspot track associated with a pulsating plume constraining ancient plate motion. Subduction-controlled plume generation can explain mantle upwelling occurring where subducted slabs forming the supercontinent had previously sunk to the base of the mantle and advected the Xiong'er mantle plume due to return flow. Tectonic motion detected by the hotspot track can account for both those regions of the supercontinent with and without LIPs. Such historical constraints on the interaction between plumes and subduction are critical in linking bottom-up and top-down tectonic processes at the dawn of the supercontinent cycle.

Neoproterozoic and early Paleozoic metamorphism recorded in gneisses from the East Kunlun Orogenic belt

The East Kunlun Orogen (EKO) is a long-lived accretionary orogenic belt that records the Paleozoic–Mesozoic amalgamation processes of the East Asia continent. The belt consists mainly of various kinds of gneisses with minor amounts of eclogite and garnet amphibolite occurring as lenses. We report zircon U–Pb ages and Hf–O isotopic compositions for the granitic gneisses and paragneisses in the Xiarihamu area near Golmud in Qinghai Province, to investigate the metamorphic history and evolution of the orogenic belt. For the granitic gneisses, zircon U–Pb chronology reveals a Neoproterozoic magmatic event and an early Paleozoic metamorphic event. The magmatic crystallization ages of the two granitic gneisses are 920 ± 6 and 929 ± 2 Ma, and yield εHf(t) values of −8.4 to 1.7 and δ18O values of 7.94–11.19‰, suggesting their derivation mainly from continental crustal materials. The detrital zircons from the paragneisses record a Neoproterozoic metamorphic event and a Paleozoic metamorphic event. Most of the detrital zircons from the two paragneiss samples yielded ages of 2.1–0.9 Ga, indicating that the sources of the sediment were formed mainly during the Neoproterozoic to Paleoproterozoic. These Neoproterozoic magmatic and metamorphic events suggest that the EKO underwent a Neoproterozoic tectonothermal event that was related to the assembly of the Rodinia supercontinent. The similar tectonic histories of the EKO and North Qaidam belt (NQB) indicate they were probably part of a single tectonic unit during the Neoproterozoic. Some of the zircons have metamorphic overgrowth rims yielding two stages of Paleozoic metamorphic ages of ca. 440 Ma (438 ± 2 Ma) and ca. 420 Ma (419 ± 6 Ma, 416 ± 6 Ma, and 423 ± 6 Ma). Combined the discover of high-pressure mineral inclusions (jadeite + quartz) in these rims with the results in previous studies, the ages of these rims (ca. 440 Ma and ca. 420 Ma) are suggested to represent of HP-UHP metamorphism of the EKO. These age data imply that the gneisses in this study might share common early Paleozoic metamorphic event with the HP–UHP eclogites in the EKO.

Contrasting mechanisms and timescales of subduction and exhumation as recorded by Paleoproterozoic and late Paleozoic high-pressure granulites in the North China Craton

Abstract The North China Craton records multiple metamorphic events related to supercontinent assembly during the Paleoproterozoic, forming Columbia, and again during the late Paleozoic, forming Pangea. Here we show that the Paleoproterozoic high-pressure granulites (HPGs) formed from enriched mid-ocean ridge basalt protoliths and record a clockwise pressure-temperature-time (P–T–t) path with prograde metamorphism at 7.8–10.0 kbar and 780–820 °C, peak granulite-facies metamorphism at 12–12.3 kbar and ∼860–880 °C, and retrograde metamorphism at 8.7–9.1 kbar and 850–855 °C. Subduction initiated prior to 1.90 Ga, with final collision and orogeny at 1.88 Ga, followed by post-collision/exhumation at 1.80 Ga, defining a prolonged exhumation period (∼90 m.y.) that occurred at a slow velocity of ∼0.16 ± 0.08 mm/y. Late Paleozoic HPGs are normal mid-ocean ridge basalt type and record a near clockwise P–T–t path, with peak/post-peak amphibolitefacies metamorphism at 11.0–12.5 kbar and 860–890 °C, isothermal decompression to 7.2–7.5 kbar and 810–820 °C, and retrogression to 5.5–7.2 kbar and 805–850 °C. Subduction initiated earlier than ca. 340 Ma, exhumation and uplift initiated at 335–309 Ma and continued to 297–287 Ma. The exhumation was short-lived (∼50 m.y.) and relatively fast (0.38 ± 0.14 mm/y). When compared to granulite-facies metamorphism documented in many Paleoproterozoic HPGs, late Paleozoic HPGs appear to commonly form with an initial period of steep subduction leading to eclogite-facies metamorphism, with subsequent exhumation to middle/lower levels of the crust. Our results further reveal that the exhumation velocity for supercontinent collision was facilitated and duration shortened through time, and that the exhumation mechanism might have been controlled by subduction angle, compression pressure, and temperature.

A crustal growth model for the eastern Central Asian Orogenic Belt: Constraints from granitoids in the Songnen Massif and Duobaoshan terrane

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.

The Formation of the North Qilian Shan through Time: Clues from Detrital Zircon Fission-Track Data from Modern River Sediments

Understanding the formation of the North Qilian Shan in the NE Tibetan Plateau provides insights into the growth mechanisms of the northern region of the plateau across time. Detrital zircon fission-track (ZFT) analyses of river sediments can provide a comprehensive understanding of the exhumation history during prolonged orogenesis. Here, we applied the detrital thermochronology approach to the Qilian Shan orogenic belt. This work presents the first single-grain detrital ZFT data from river-bed sediments of the upper Hei River catchment in North Qilian Shan. The single ZFT ages are widely distributed between about 1200 Ma and about 40 Ma. These data record the protracted history of the Qilian Shan region from the Neoproterozoic evolution of Rodinia and late Paleozoic amalgamation of Central Asia to the accretion of the Gondwanian blocks during the Meso-Cenozoic era. Strong post-magmatic cooling events occurred in North Qilian Shan at 1200~1000 Ma, corresponding to the assembly of the Rodinia supercontinent. The age population at 800 Ma documents the oceanic spreading in the late Neoproterozoic dismantling of Rodinia. ZFT ages ranging from about 750 Ma to 550 Ma (with age peaks at 723 Ma and 588 Ma) are consistent with the timing of the opening and spreading of the Qilian Ocean. The age peaks at 523 Ma and 450 Ma mark the progressive closure of that ocean ending with the collision of the Qilian block with the Alxa block—North China craton in the Devonian. The Qilian Ocean finally closed in Late Devonian (age peak at 375 Ma). In the late Paleozoic (275 Ma), the subduction of the Paleotethys Ocean led to extensive magmatic activity in the North Qilian Shan. During the Lower Cretaceous (145 Ma), the accretion of the Lhasa block to the south (and potentially the closure of the Mongol-Okhotsk Ocean to the northeast) triggered a renewed tectonic activity in the Qilian Shan. Finally, a poorly defined early Eocene exhumation event (50 Ma) suggests that the NE Tibetan Plateau started to deform nearly synchronously with the onset of the India-Asia collision. This study demonstrates the usefulness of combining modern-river detrital thermo-/geochronological ages and bedrock geochronological ages to understand large-scale orogenic evolution processes.

Granitic Magmatism in Eastern Tethys Domain (Western China) and their Geodynamic Implications

AbstractWestern China locates in the eastern section of the Tethys domain, granitic rocks in this region with variable formation ages and geochemistry record key information about the crust‐mantle structure and thermal evolution during the convergent process of Tethys. In this study, we focus on some crucial granitic magmatism in the western Yangtze, Qinling orogen, and western Sanjiang tectonic belt, where magma sequence in the convergent orogenic belt can provide important information about the crust‐mantle structure, thermal condition and melting regime that related to the evolution processes from Pre‐ to Neo‐Tethys. At first, we show some features of Pre‐Tethyan magmatism, such as Neoproterozoic magmatism (ca. 870–740 Ma) in the western margin of the Yangtze Block were induced by the assembly and breakup of the Rodinia supercontinent. The complication of voluminous Neoproterozoic igneous rocks indicated that the western Yangtze Block underwent the thermodynamic evolution from hot mantle‐cold crust stage (ca. 870–850 Ma) to hot mantle and crust stage (ca. 850–740 Ma). The Neoproterozoic mantle sources beneath the western Yangtze Block were progressively metasomatized by subduction‐related compositions from slab fluids (initial at ca. 870 Ma), sediment melts (initial at ca. 850 Ma), to oceanic slab melts (initial at ca. 825–820 Ma) during the persistent subduction process. Secondly, the early Paleozoic magmatism can be well related to three distinctive stages (variable interaction of mantle‐crust to crustal melting to variable sources) from an Andeans‐type continental margin to collision to extension in response to the evolution of Proto‐Tethys and final assembly of Gondwana continent. Thirdly, the Paleo‐Tethys magmatism, Triassic granites in the Qinling orogenic display identical formation ages and Lu‐Hf isotopic compositions with the related mafic enclaves, indicate a coeval melting event of lower continental crust and mantle lithosphere in the Triassic convergent process and a continued hot mantle and crust thermal condition through the interaction of subducted continental crust and upwelling asthenosphere. Finally, the Meso‐ and Neo‐Tethyan magmatism: Early Cretaceous magmatism in the Tengchong Block are well responding to the subduction and closure of Bangong‐Nujiang Meso‐Tethys, recycled sediments metasomatized mantle by subduction since 130 Ma and subsequently upwelling asthenosphere since ca. 122 Ma that causes melting of heterogeneous continental crust until the final convergence, this process well recorded the changing thermal condition from hot mantle‐cold crust to hot mantle and crust; The Late Cretaceous to Early Cenozoic magmatism well recorded the processes from Neo‐Tethyan ocean slab flat subduction, steep subduction, to initial collision of India‐Asia, it resulted in a series of continental arc magmatism with enriched mantle to crustal materials at Late Cretaceous, increasing depleted and/or juvenile materials at the beginning of early Cenozoic, and increasing evolved crustal materials in the final stage, implying a continued hot mantle and crust condition during that time. Then we can better understand the magmatic processes and variable melting from the mantle to crust during the evolution of Tethys, from Pre‐, Paleo‐, Meso‐, to Neo‐, both they show notably intensive interaction of crust‐mantle and extensive melting of the heterogeneous continent during the final closure of Tethys and convergence of blocks, and thermal perturbation by a dynamic process in the depth could be the first mechanism to control the thermal condition of mantle and crust and associated composition of magmatism.

A2-Type Granites from the Bastar Craton, South-Central India, and Their Implication in Archean-Paleoproterozoic Tectonics in Indian Peninsula

Abstract This communication reports novel geochemical and geochronological data of granite from the southeastern part of the Bastar Craton, Central India. The studied samples are leucocratic in appearance and composed of quartz, K-feldspar, plagioclase feldspar, and biotite in decreasing order of abundances. Apatite, sphene, and zircon occur as accessory minerals. The SiO2 and Al2O3 content of the studied sample varies between 61 and 69 wt.% and 13 and 15 wt.%, respectively. The alkali oxides, K2O, and Na2O content ranges between 3 and 6 wt.% and 2 and 3 wt. %, respectively. In the primitive mantle normalized spider diagram, the granites exhibit a negative Nb–Ti, Sr anomaly, and a positive Pb–Th anomaly. Similarly, in the REE normalized spider plot, the granites exhibit a strongly fractionated trend La/YbCN=10.90−28.4 with a negative Eu anomaly (0.42-0.70). The zircon saturation in silicate melt yields crystallization temperature (Tzr) ~650 to 800°C for the Eastern Bastar Craton rocks. The P-T pseudosection modeling implies EBC granites which are crystallized at 700-750°C, at 0.4 to 0.6 GPa. The SHRIMP U-Pb ages from magmatic zircon yield an upper intercept at ~2470 Ma and a lower intercept at ~2100 Ma. When combined with the results of P-T pseudosection modeling, the geochemical and geochronological data classifies the Eastern Bastar Craton rocks as A2 granites that were emplaced during the amalgamation of Archean blocks leading to extended Ur formation. The ~2100 Ma age is correlated with mafic dyke emplacement and the Bastar Craton–Yilgarn Craton block disintegration before Paleoproterozoic Columbia supercontinent assembly.

Structural Anatomy of the Intraterrane Shear Zones in the Archean Bundelkhand Craton, North-Central India and Its Possible Linkage to Supercontinent Assembly: Insights from Field- and AMS-Based Kinematic Analysis

Abstract Delineation and characterization of the intraterrane shear zones (ITSZs) are very significant in establishing suitable models to understand the tectonic evolution of continental blocks and often provide crucial information on supercontinent assembly. The granitoid rocks of the Bundelkhand Craton (BC) host mesoscale ductile shear zones of varying width and direction and typically represent decoupling zones (high and low strain), characteristic of ITSZs. The detailed study on the structural anatomy and nucleation of the ductile shear zones in the BC suggests the presence of four distinct sets of ITSZs along ~N-S, ~NE-SW, ~NW-SE, and ~ E-W directions. The nucleation of the ITSZs in the granitoid rocks is possibly a result of reactivation of the precursor fractures due to the rheological transformation induced by a fluid phase, which percolated through the fractures. Also, the thickness of the ultramylonite zone in the ITSZs is attributed to the width and style of the brittle fracturing. Here, we also construe a relative chronology of the development of fabric elements related to the ITSZs in BC with the help of cross-cutting relationships as observed in the field and further corroborated it to the available chronological data. This suggests, ~E-W trending ITSZs along the Bundelkhand tectonic zone (BTZ) and Raksa shear zone (RSZ) as the oldest followed by the evolution of ~N-S, ~NE-SW, and ~ NW-SE trending ITSZs. The kinematic analysis of these ITSZs, with the help of angular relationship between the measured mylonitic foliation and determined magnetic foliation data (by AMS analysis), suggests that fabric development in the ITSZs is dominantly governed by general shear except the oldest ~E-W trending ITSZs, which shows pure shear dominated progressive deformation. Also, with the help of field evidences and magnetic fabric analysis, we conclude that transpression was involved over a protracted period for the evolution of the ITSZs in the BC. Finally, we argue that the BTZ served as the site for the localization of the ~E-W trending ITSZs and represents the zone of amalgamation between North BC and South BC during the formation of Kenorland.

About this title - Large Igneous Provinces and their Plumbing Systems

Identification of large-volume, short-duration mafic magmatic events of intraplate affinity in both continental and oceanic settings on the Earth and other planets provides invaluable clues for understanding several vital geological issues of current concern. Of particular importance is understanding the assembly and dispersal of supercontinents through Earth's history, dramatic climate change events including mass extinctions, and processes that have produced a wide range of large igneous province (LIP)-related resources, such as Ni–Cu–PGE, Au, U, base metals and petroleum. This volume comprises 21 contributions on the latest developments and new information on LIPs and their plumbing systems and presents methodical studies on different components of LIP plumbing systems. These articles are especially helpful in understanding continental break-up events, regional domal uplift and a variety of metallogenic systems, as well as the temporal and spatial distribution of LIPs, their origin and their likely links to mantle plumes/superplumes.