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The Trans‐North China Orogen (TNCO) is a major Palaeoproterozoic collisional orogen in the North China Craton and has experienced complex tectonic evolution during the assembly of the Eastern and Western Blocks. The vestiges of subducted oceanic crust preserved in this orogen can be used to gain insights into the subduction–collision process associated with the Palaeoproterozoic orogeny. In this study, we investigate garnet amphibolites from the Wanzi Group in the Fuping Complex along the TNCO through integrated petrography, mineral chemistry, phase equilibrium modelling and zircon U–Pb geochronology. Three stages of metamorphic mineral assemblages are identified as follows: (i) the prograde assemblage is preserved as plagioclase, amphibole, biotite and quartz inclusions in garnet porphyroblasts; (ii) the peak mineral assemblage includes coarse‐grained amphibole, garnet, plagioclase, ilmenite, biotite and quartz; and (iii) the retrograde assemblage is mainly represented by the corona of amphibole, plagioclase and biotite in the matrix. Petrological features and phase equilibrium modelling define a clockwise pressure–temperature path involving a prograde stage of 7.2–9.6 kbar and <670°C, peak conditions of 10.0–10.2 kbar and 690–810°C, and a retrograde stage with near‐isothermal decompression to ~7.4 kbar and cooling. Zircon U–Pb dating shows weighted mean ages of 1848 ± 22 Ma and 1836 ± 31 Ma, representing the growth of zircon in the retrograde stage during the uplift and cooling process. In combination with available data from the TNCO, the post‐peak decompression and cooling process is inferred to be long‐lived during 1.90–1.76 Ga, following collision along the TNCO that occurred during 1.97–1.90 Ga, ultimately leading to the final assembly of the North China Craton. [ABSTRACT FROM AUTHOR]

Subduction zones are the gateways of large-scale material and energy exchange. The SW Japan region is one of the important regions to understand ongoing convergent margin processes with continuous island arc magmatism. Here we investigate the bimodal magmatic suites from the Tsukuba area in Japan based on petrology, geochemistry and zircon U-Pb-Hf isotopes. Magmatic rocks in the Tsukuba area comprise two compositionally different groups: 1) a mafic group comprising Hbl-gabbros of ~66 Ma and 2) a felsic group represented by two pulses of granitoids at ~66 Ma and ~78 Ma, respectively. All these rocks display calc-alkaline affinity and negative Nb, and Ta anomalies, with a bimodal classification represented by a significant silica gap between the mafic and felsic members. The Hbl-gabbro witnessed plagioclase and amphibole fractionation as evidenced by the humped REE pattern and positive Eu and Sr anomalies. Zircon grains from the Hbl-gabbros show ƐHf (t) values in the range of −7.7 to −4.0 with a peak at −6.4, indicating an enriched mantle source modified by slab-derived fluids. The petrological and geochemical characteristics of Hbl-gabbros are similar to those in the magmatic suite of SW Japan, suggesting that Cretaceous arc magmatism in Tsukuba is an extension of the coeval magmatic belt in SW Japan. Two pulses of granitoids identified in this study are similar in composition and are both classified as I-type granite. The relative uniform high SiO2 (70–75%) and large variation of Hf isotope (−21.0 to −4.0) indicates the granitoids formed by lower crustal melting. The Hf model ages (2479–1392 Ma) of granitoids are significantly older than those of coeval granitoids in SW Japan which show Nd model ages at 1435–748 Ma. This indicates that the arc magmatism in the Tsukuba area involved older lower crust linked to a possible micro-continent derived from the Southern Korean Peninsula. [ABSTRACT FROM AUTHOR]

[Display omitted] • The Keluo Complex is dominated by at least four stages of deformed magmatic rocks. • Two major deformation events were recognized in this Complex. • D 1 is related to the subduction and closure of the Mongol-Okhotsk Ocean. • D 2 resulted from the superimposition of the two extensional settings. The Da Hinggan Mountains (DHM) are located in the eastern segment of the Central Asian Orogenic Belt (CAOB) and represent a prominent geomorphic marker of NE China, although its evolution history and exhumation/uplift mechanisms remain equivocal. Here, we present results from a comprehensive study on the field and micro-structures, kinematics, rheology, quartz EBSD fabrics, geochemistry and geochronology of the Keluo Complex (KC) exposed in the northern DHM. The KC is dominated by deformed Early Carboniferous to earliest Permian rocks (337–297.1 Ma) and is invaded by Early Mesozoic multi-stage granitic intrusions (219.8–175.5 Ma). These were further overprinted by magmatism, metamorphism, and deformation during the Late Jurassic (152.0–157.7 Ma) and late Early Cretaceous (118.3 Ma). The latest Carboniferous/earliest Permian rocks formed in a post-collisional extensional environment that might be related to the collision of the Xing'an and Songnen massifs. The Early Mesozoic rocks were derived from magma generated by partial melting of the lower continental crust within an active continental margin setting related to the subduction of the Mongol-Okhotsk Ocean. Two prominent deformation events (D 1 and D 2) were recognized in the KC, which occurred in Late Jurassic and late Early Cretaceous. The D 1 is dominated by SW-trending sinistral ductile shearing accompanied by moderate to high-temperature deformation (500–600 °C) resulting from NW–SE compression. The D 2 is a bi-directional extensional and detachment deformation corresponding to a low temperature (300–400 °C) deformation developed at a shallow-level ductile regime resulting from NW–SE extension. The D 1 deformation was influenced by subduction and closure of the Mongol-Okhotsk Ocean, whereas the D 2 deformation is correlated to the superposition of the extension after the closure of the Mongol-Okhotsk Ocean and the rollback of the Paleo-Pacific Plate. Our results provide new insights into the tectonic history of the DHM domain of the CAOB. [ABSTRACT FROM AUTHOR]

The North China Craton (NCC), which underwent multiple subduction and lithospheric destruction during the Mesozoic, is well known for hosting some of the world-class gold deposits. In many cases, Mesozoic mafic dykes are associated with the gold deposits, although there has been no systematic studies aimed to integrate the characteristics of these dykes in different regions of the NCC. Here we investigate diabase and lamprophyre dyke suites in the Xiaoqinling region along the southern margin of the NCC, and compile the published geochronological, geochemical and isotopic data for regional mafic dykes and gold deposits from the major gold belts including Jiaodong, Xiaoqinling and central NCC. Zircon U-Pb data show the mafic dykes in Xiaoqinling were emplaced in two episodes at 219–227 Ma and 121–137 Ma, and their εHf(t) values (ranging from −2.1 to 3.8 and −13.6 to 1.6 respectively) suggest increasing input of lithospheric materials in the Early Cretaceous dykes. The compiled geochemical data on the mafic dykes from different regions in the NCC show that the magmatic evolution involved olivine and clinopyroxene fractional crystallization with limited crustal contamination and subduction-related fluid metasomatism. The geochemical and isotopic signature suggests multiple sources for the parent magma of the mafic dykes ranging from convective asthenospheric mantle to ancient lithospheric mantle, with the magma source characterized by enriched mantle (EM2 or EM2+ EM1), and that signatures might be potential for gold mineralization. Further, most dykes are coeval and cospatial with gold deposits in the NCC. The geochronological data show that small amount of both Mesozoic dykes and gold deposits formed in Triassic whereas the peak formed in Cretaceous following slab roll back of the Pacific plate subducting from the east during 145–110 Ma. We envisage that the tectonic extension associated with Pacific slab subduction contributed to the magmatism and gold mineralization in the NCC. [ABSTRACT FROM AUTHOR]

The Permo-Triassic adakitic magmatism in the southern Korean Peninsula preserves important tectonomagmatic records along the East Asian continental margin. In this study, we present SHRIMP/LA–MC–ICPMS U-Pb zircon ages and Hf isotope signature with whole-rock geochemical compositions of the Middle Permian to Middle Triassic granitoid gneiss-granitoid suites and the Middle to Late Triassic plutonic rocks in the southeastern Korean Peninsula. The former yields three age groups of ca. 272–263 Ma, ca. 258–251 Ma and ca. 243–240 Ma, respectively. The latter group yields ca. 237–216 Ma ages, indicating a long term magmatism that lasted from the Middle Permian to late Triassic. The granitoid gneiss-granitoid suites have chemical compositions similar to high silica adakitic rocks, showing high SiO 2 (59.55–73.97 wt.%), Na 2 O (3.55–5.30 wt.%), Sr/Y (30–401), and La/Yb N (11–173), and low MgO (0.18–1.82 wt.%), Y (2–14 ppm) and Yb N (2–7). These rocks are peraluminous with high Ba and Sr, and show relatively high K 2 O contents and K 2 O/Na 2 O ratios (> 0.7), with positive correlation between La/Yb N vs. Sr/Y ratios and high initial Sr ratios. These features reflect different contribution of the slab-derived adakite melts that interacted with peridotitic mantle in the metasomatized mantle wedge and the Middle Paleoproterozoic lower crustal basement of the Yeongnam Massif. On the contrary, the Triassic alkaline magmatism in the Yeongnam Massif is alternatively interpreted either by a tectonic switch to the extension-dominated arc system or by a delamination of an overthickened arc. The results from this study offer important evidence for a common subduction-accretion system existed between the North and South China Cratons and microcontinents between them along margins of the East Asian continental blocks, with different plate interaction in different locations generating distinct magmatic suites. [Display omitted] • The Permo-Triassic magmatic m rocks in southern Korea are adakitic rocks, having similar geochemical characteristics to adakites. • Tectonomagmatic records preserved in them might be linked to the magmatic responses to the Permo-Triassic tectonic events in East Asia. • The controversial tectonic nature of Late Triassic magmatism remains for further research in the Korean Peninsula. [ABSTRACT FROM AUTHOR]

The Gejiu alkaline complex (GAC) within the western part of the Youjiang Basin provides a window to investigate the evolution in the junction of Cathaysia, Yangtze and Indochina blocks. Here, we investigate the GAC in terms of their petrology, zircon U–Pb geochronology, whole‐rock geochemistry, and Sr–Nd isotopic data to gain insights into the origin and evolution of the alkaline magma. The GAC is lithologically composed of alkali syenites and feldspathoid syenites, in which some were altered into sericite syenites. Zircon U–Pb dating of the alkali syenites yielded an age of 85.03 ± 0.47 Ma, which is slightly older than the feldspathoid syenites. The alkali syenites and feldspathoid syenites are silica‐saturated and silica‐undersaturated, respectively, and are characterized by high alkalinity with K2O + Na2O of 11.55–17.08 wt% and Al2O3 of 18.57–22.49 wt%, low MgO of 0.11–1.39 wt%, weakly negative Eu anomalies, enrichments of LILEs such as Th and U, HFSEs like Zr and Hf but depletion of Ba, Sr, Nb, Ta, P, Ti, strongly fractionated LREEs to HREEs. Their uniform Sr–Nd isotope composition with initial 87Sr/86Sr = 0.708802–0.710571 and εNd(t) = −7.1 to −6.6 indicates that they were products of a homologous magma. They crystallized at c. 810–956°C and have a relatively high magmatic oxygen fugacity. Our geochemical and isotopic data proved that the GAC magma was derived from the low‐degree partial melting (<10%) of a phlogopite‐bearing‐enriched mantle that was metasomatized by subducting sediments and originated possibly from the spinel and garnet transition zone at a depth of 60–80 km and a pressure of about 1.8–2.4 Gpa. The primary magma experienced protracted two‐stage crystal fractionation of clinopyroxene+amphibole and biotite+K‐feldspar, forming alkali syenites and feldspathoid syenites. Crustal contamination plays a negligible role in their formation. Considering previous tectonic studies, it was therefore proposed that the GAC formed in an extensional tectonic setting related to the Neo‐Tethyan tectonic regions during the Late Cretaceous. [ABSTRACT FROM AUTHOR]

Numerous granitoid suites exposed in the Qilian orogen, NE Tibetan Plateau preserve important records of the tectonic evolution of this orogen. Here we present zircon U–Pb, zircon rare earth elements (REEs), and whole‐rock geochemical and Sr–Nd–Hf isotopic data on Niuxinshan granitoids in the North Qilian orogen, with a view to constrain their petrogenesis and timing of emplacement, as well as to gain new insights into the Early Palaeozoic tectonic evolution of the Qilian orogen. Zircon U–Pb data show multiple concordant ages of ~517, 455–425, 397–389, and 351–319 Ma for syenogranite, and ages of ~758 and 724 Ma together with some scattered Early Mesozoic discordant ages for porphyritic granite, suggesting episodic magmatism from Neoproterozoic to Early Mesozoic. Zircon ∑REEs range from 276.43 to 4,582.32 ppm, and are characterized by depletion of light REEs (LREEs) and enrichment heavy REEs (HREEs) with negative Eu anomalies, indicating a mixture of magmatic and hydrothermal zircons. Whole‐rock geochemical data show similar variation of LREEs, large‐ion lithophile elements (LILEs), HREEs, and high‐field‐strength elements (HFSEs) with zircon REEs, with Eu, Ba, P, and Ti negative anomalies and Rb, U, and Pb positive anomalies. Based on their formation ages, two groups of granitoids are identified. Group I rocks (Early Palaeozoic) are represented by I‐type granites whereas Group II rocks (Early Mesozoic) are of S‐type. Whole‐rock Sr–Nd–Hf isotopes display (87Sr/86Sr)i ratios of 0.707085–0.709591, εNd(t) values of −5.3 to −2.3, εHf(t) values of −2.2 to 0, and two‐stage model (Nd and Hf) ages of 1.6–1.4 Ga for Group I rocks, and of 0.728156–0.734113, −9.4 to −9.3, −10.6 to −6.9, and 2.1–1.9 Ga for Group II rocks. Accordingly, we infer that the magma for Group I was sourced from the partial melting of basaltic protoliths in the mafic lower crust and underwent fractional crystallization. Group II was derived from metasedimentary protoliths through reworking of ancient Palaeoproterozoic crustal components. Integrating the results from this study with those from previous studies on Niuxinshan granitoids, we argue that the southward subduction model of the North Qilian Ocean beneath the Qilian Block during the Early Palaeozoic might be a more reasonable scenario. However, the Early Mesozoic magmatic event reported here remains equivocal in the North Qilian orogen. [ABSTRACT FROM AUTHOR]

The Bhavani Suture Zone in the Southern Granulite Terrane marks the zone of amalgamation of the Neoarchean Nilgiri Block and the northwestern Madurai Block in southern India. Here, we report detailed petrological, geochemical, and geochronological data on the Mettupalayam mafic–ultramafic complex within this suture zone with a view to evaluate the tectonothermal history of the Bhavani Suture Zone and adjoining crustal blocks. The metamorphosed complex includes charnockite, hornblende‐biotite gneiss, mafic granulite, amphibolite, garnet‐bearing mafic granulite, and dioritic gneiss along with metamorphosed banded iron formation. The mafic granulite and the dioritic gneiss occur as concordant layers of varying thickness within the hornblende‐biotite gneiss. The salient geochemical features of the mafic granulite and the dioritic gneiss including the enrichment of large‐ion lithophile elements and depletion of high‐field‐strength elements suggest a subduction‐related arc magmatic setting. However, the amphibolites show MORB‐related affinity, suggesting its formation from a N‐MORB‐related source and their accretion together with the overlying banded iron formation. The peak metamorphic conditions of the garnet‐bearing mafic granulite were estimated using conventional geothermobarometers as 800–820 °C/8.5–9.2 kbar, which we further confirm through phase equilibrium modelling in the Na2O–CaO–K2O–FeO–MgO–Al2O3–SiO2–H2O–TiO2–Fe2O3 (NCKFMASHTO) system. Magmatic zircons with high Th/U ratio from the amphibolite display a well‐defined discordia with an upper intercept age of 2,600 ± 38 Ma. Zircon grains from the dioritic gneiss show weighted mean 206Pb/207Pb age of 2,524 ± 6 Ma from concordant zircon spots and a comparable upper intercept age of 2,562 ± 34 Ma from discordant zircon spots, indicating protolith emplacement related to Neoarchean arc magmatism as inferred from our geochemical data. The thin overgrowth rims around the magmatic zircon grains in the amphibolite yielded an upper intercept age of 2,520 ± 20 Ma, which is comparable with the protolith crystallization age of the dioritic gneiss. Slightly younger weighted mean 207Pb/208Pb ages of 2,463 ± 27 Ma (from dioritic gneiss) and 2,422 ± 30 Ma (from amphibolite) are also obtained from the metamorphic zircon rims. These ages are correlated to the timing of high‐grade metamorphism associated with final collision of the Nilgiri Block and the northwestern Madurai Block. Similar Neoarchean–Paleoproterozoic magmatism and high‐grade metamorphism were reported from many localities south of the Dharwar Craton. Our study further confirms the previous tectonic model that envisages multiple subduction and collision of magmatic arcs and continental fragments towards the Dharwar Craton during the Archean–Paleoproterozoic transition. [ABSTRACT FROM AUTHOR]

The Dharwar Craton is a composite Archean cratonic collage that preserves important records of crustal evolution on the early Earth. Here we present results from a multidisciplinary study involving field investigations, petrology, zircon SHRIMP U–Pb geochronology with in-situ Hf isotope analyses, and whole-rock geochemistry, including Nd isotope data on migmatitic TTG (tonalite-trondhjemite-granodiorite) gneisses, dark grey banded gneisses, calc-alkaline and anatectic granitoids, together with synplutonic mafic dykes along a wide Northwest – Southeast corridor forming a wide time window in the Central and Eastern blocks of the Dharwar Craton. The dark grey banded gneisses are transitional between TTGs and calc-alkaline granitoids, and are referred to as 'transitional TTGs', whereas the calc-alkaline granitoids show sanukitoid affinity. Our zircon U–Pb data, together with published results, reveal four major periods of crustal growth (ca. 3360-3200 Ma, 3000-2960 Ma, 2700-2600 Ma and 2570-2520 Ma) in this region. The first two periods correspond to TTG generation and accretion that is confined to the western part of the corridor, whereas widespread 2670-2600 Ma transitional TTG, together with a major outburst of 2570–2520 Ma juvenile calc-alkaline magmatism of sanukitoid affinity contributed to peak continental growth. The transitional TTGs were preceded by greenstone volcanism between 2746 Ma and 2700 Ma, whereas the calc-alkaline magmatism was contemporaneous with 2570–2545 Ma felsic volcanism. The terminal stage of all four major accretion events was marked by thermal events reflected by amphibolite to granulite facies metamorphism at ca. 3200 Ma, 2960 Ma, 2620 Ma and 2520 Ma. Elemental ratios [(La/Yb) N , Sr/Y, Nb/Ta, Hf/Sm)] and Hf-Nd isotope data suggest that the magmatic protoliths of the TTGs emplaced at different time periods formed by melting of thickened oceanic arc crust at different depths with plagioclase + amphibole ± garnet + titanite/ilmenite in the source residue, whereas the elemental (Ba–Sr, [(La/Yb) N , Sr/Y, Nb/Ta, Hf/Sm)] and Hf-Nd isotope data [εHf (T) = −0.67 to 5.61; εNd (T) = 0.52 to 4.23; ] of the transitional TTGs suggest that their protoliths formed by melting of composite sources involving mantle and overlying arc crust with amphibole + garnet + clinopyroxene ± plagioclase + ilmenite in the residue. The highly incompatible and compatible element contents (REE, K–Ba–Sr, Mg, Ni, Cr), together with Hf and Nd isotope data [εHf (T) = 4.5 to −3.2; εNd (T) = 1.93 to −1.26; ], of the sanukitoids and synplutonic dykes suggest their derivation from enriched mantle reservoirs with minor crustal contamination. Field, elemental and isotope data [εHf (T) = −4.3 to −15.0; εNd (T) = −0.5 to −7.0] of the anatectic granites suggest their derivation through reworking of ancient as well as newly formed juvenile crust. Secular increase in incompatible as well as compatible element contents in the transitional TTGs to sanukitoids imply progressive enrichment of Neoarchean mantle reservoirs, possibly through melting of continent-derived detritus in a subduction zone setting, resulting in the establishment of a sizable continental mass by 2700 Ma, which in turn is linked to the evolving Earth. The Neoarchean geodynamic evolution is attributed to westward convergence of hot oceanic lithosphere, with continued convergence resulted in the assembly of micro-blocks, with eventual slab break-off leading to asthenosphere upwelling caused extensive mantle melting and hot juvenile magma additions to the crust. This led to lateral flow of hot ductile crust and 3D mass distribution and formation of an orogenic plateaux with subdued topography, as indicated by strain fabric data and strong seismic reflectivity along an E-W crustal profile in the Central and Eastern blocks of the Dharwar Craton. Image 1 • Multi-stage Archean crustal growth ca. 3360-3200 Ma, ca. 3000-2960 Ma, ca. 2700-2600 Ma and ca. 2570-2520 Ma. • Secular changes in the composition of granitoids through time imply increasing involvement of enriched peridotitic mantle. • Convergence of oceanic lithosphere and eventual slab breakoff lead to asthenosphere upwelling. • Lateral flow of hot orogenic crust lead to orogenic plateau formation with subdued topography. [ABSTRACT FROM AUTHOR]

Ocean island basalts (OIBs) and associated sedimentary units form part of the ocean plate stratigraphy accreted onto island arcs or continental arcs and provide important insights into convergent margin processes. Here, we investigate some of the typical localities of Sanpozan, Shirakidani, and Kamiananai within the Chichibu composite belt in Kochi, SW Japan, where the accretionary complexes incorporate OIBs and sedimentary rocks that preserve the travelogue of an oceanic plate from a mid‐oceanic ridge (MOR) to subduction zone. We present petrology and geochemistry, as well as zircon U–Pb geochronology and REE data of the accreted OIB and sedimentary formations from Sanpozan, Shirakidani, and Kamiananai. The OIBs are enriched in LILE and LREE and depleted in HREE. The chondrite‐normalised REE patterns of zircon grains from OIBs and sedimentary rocks display LREE depletion and HREE enrichment, sharply positive Ce and Sm anomalies and negative Pr and Eu. LA‐ICP‐MS U–Pb geochronology of zircon grains from the OIBs shows three major populations with 206Pb/238U mean ages of 164–456, 724–955, and 1,638–2,202 Ma. The diverse ages suggest heterogeneous recycled source components in the plume‐related upwellings that generated the OIBs, as well as different times of formation and accretion of the Palaeozoic and Mesozoic oceanic islands. The dominant population of zircon grains from the sedimentary units shows 206Pb/238U mean ages of 147 and 288 Ma and indicate a major change in the provenance regime with subduction and the disappearance of older arcs attesting to the destruction of continental crust in convergent margins. [ABSTRACT FROM AUTHOR]

[Display omitted] • First report of oldest sedimentation in Chitradurga Group of Dharwar Craton, India. • Regional oxic pools in the passive margin mediated by microbial growth. • Paleo–Mesoarchean Mn sedimentation inferred from detrital zircon U-Pb ages of 3230 ± 52 Ma. The early Archean oceans were marked by significant redox changes which have subsequently shaped the Earth's biosphere. Archean chemical sediments of banded Iron and Manganese formations provide important geochemical proxies for these historical shifts in the redox conditions and to trace the ancient sedimentation patterns and protoliths. In this study, we investigate the proto-ore of the Archean Mn-formations of the Sandur, Chitradurga and Shimoga greenstone belts of Dharwar Craton of southern Peninsular India, which is geochemically characterised as quartz arenites, Mn-arenites, Fe-arenites, Mn-argillites and Fe-argillites. The geochemical systematics suggest their deposition in shallow to deeper shelf in the Archean proto-ocean. The detrital zircon U-Pb systematics of Mn arenites and argillites indicate their maximum depositional age of 3230 ± 52 Ma representing the oldest onset of sedimentation during the Paleo–Mesoarchean timeframe in the Chitradurga Group of Dharwar Supergroup. The detrital influx proxies suggest variations in sedimentation rates associated with the Archean transgressive–regressive cycles and fluctuating hydrodynamic conditions, together reflecting an increasing trend in the contributions of recycled sediment from Sandur to Chitradurga and Shimoga greenstone belts. The available detrital zircon ages of the Mn arenites and argillites from these greenstone belts indicate a ∼ 600 Ma prolonged period of Mn deposition for which high-T hydrothermal fluids from Archean mid-oceanic ridges supplied the manganese. The trace element compositions of the concordant detrital zircons suggest 3.3–3.1 Ga Dharwar basement TTG/granitoid source which is corroborated by the zircon crystallization temperatures of 690–820 °C. The source-normalised α-dose rates of the detrital zircons signify greater degrees of sediment transport and multi-cycle nature which correspond to the earliest episode of crustal growth in the Indian sub-continent associated with the Mesoarchean Ur supercontinent. The clastic-chemogenic sedimentation attained through concomitant detrital sediment–seawater-metalliferous hydrothermal fluid mixing at an epicontinental passive margin resulted in the deposition of Mn-arenites and argillites closer to the higher Eh shore, while the Fe-rich sediments formed at a relatively deeper shelf characterised by comparatively lower Eh and more alkaline conditions. The comprehensive geochemical and geochronological data of the Archean Mn arenite-argillite sequences reveal the significance of regional episodes of ocean oxygenation at the shallow shelves of Archean oceans prior to great oxygenation event (GOE) that was mediated by the prolific growth of ancient microbiota which transformed the Earth to a more habitable planet. [ABSTRACT FROM AUTHOR]

Magmatic pulses in intraplate sedimentary basins are windows to understand the tectonomagmatic evolution and paleaoposition of the Basin. The present study reports the U–Pb zircon ages of mafic flows from the Cuddapah Basin and link these magmatic events with the Pangean evolution during late Carboniferous–Triassic/Phanerozoic timeframe. Zircon U–Pb geochronology for the basaltic lava flows from Vempalle Formation, Cuddapah Basin suggests two distinct Phanerozoic magmatic events coinciding with the amalgamation and dispersal stages of Pangea at 300 Ma (Late Carboniferous) and 227 Ma (Triassic). Further, these flows are characterized by analogous geochemical and geochronological signatures with Phanerozoic counterparts from Siberian, Panjal Traps, Emeishan and Tarim LIPs possibly suggesting their coeval and cogenetic nature. During the Phanerozoic Eon, the Indian subcontinent including the Cuddapah Basin was juxtaposed with the Pangean LIPs which led to the emplacement of these pulses of magmatism in the Basin coinciding with the assemblage of Pangea and its subsequent breakup between 400 Ma and 200 Ma. Image 1 • First report of Phanerozoic magmatism in the Mesoproterozoic Cuddapah basin. • U–Pb zircon ages of mafic flows reveal two distinct phases of magmatism. • Analogous geochemical signatures with global Permo-Carboniferous counterparts. • Coeval magmatism with amalgamation and dispersal stages of Pangea respectively. [ABSTRACT FROM AUTHOR]

Imprints of Marion hotspot magmatism representing the final stages of rifting between India and Madagascar from the Gondwana assembly occur scattered in several localities of southern India. In this study, we report evidence for rift‐related Santonian magmatism from alkali gabbro in the Madurai Block and present mineralogical, petrological, zircon U–Pb geochronological, and whole‐rock geochemical data on the Mundanmudi gabbroic complex. The rock shows mesocumulate textures with plagioclase laths forming the triple junctions and porphyritic texture with hornblende and clinopyroxene as phenocrysts. Geochemically, the gabbros are characterized by moderate to high SiO2 (50–58 wt.%), alkalies (4.14–7.00 wt.%), and high TiO2 (1.71–4.22 wt.%), with calc‐alkaline to high‐K alkaline affinity. Chondrite‐normalized REE patterns are highly fractionated with LREE enrichment relative to HREE and absence of Eu anomalies. The primitive mantle normalized trace element patterns have LILE enrichment relative to HFSE, exhibiting negative anomalies at Nb, Zr, and Ti. The HFSE relationships indicate a within‐plate tectonic setting for the genesis of these gabbros. The major element tectonic discrimination plots suggest MORB‐OFB affinity which is also supported by the Nb–Th relationship endorsing the divergent tectonic processes responsible for the generation of these gabbros. The zircon U–Pb mean age of ca. 85 Ma represents the magmatic emplacement age within a rift‐related tectonic setting during the Santonian (late Cretaceous). Based on the LREE and HREE relationship, it is inferred that the parental magma might have been derived at garnet lherzolite depths above the Marion plume, possibly correlatable with the large igneous province generated at this time in Madagascar. Our study provides new evidence for the final phase of the magmatism at ca. 85 Ma related to India–Madagascar rifting. [ABSTRACT FROM AUTHOR]

Paleoproterozoic granulite facies rocks are widely distributed in the North China Craton (NCC). The Huai'an terrane, located within the northern segment of the Trans-North China Orogen (TNCO), a major Paleoproterozoic collisional belt in the central NCC expose mafic and pelitic granulites as well as TTG (tonalite-trondhjemite-granodiorite) gneisses. Here we investigate the pelitic granulites from this complex and identify four distinct mineral assemblages corresponding to different metamorphic stages. The prograde metamorphism (M1) is recorded by relict biotite and the compositional profile of X ca (grt) isopleths. The P max (M2) is distinguished by the X ca (grt) isopleths, which corresponds to the kyanite stable area with an inclusion mineral assemblage of Grt-c–(Ky)-Qz-Rt-Kfs-liq suggesting that the pressures were higher than 12 kbar with a temperature below 900 °C. However, kyanite is absent in thin sections suggesting its consumption during later stages. The T max metamorphism (M3) is characterized by the assemblage: Grt-m-Qz-Pl-Rt-Kfs-Sil-liq in the garnet mantle and also reflected in the compositional profile. Two-feldspar geothermometry yields a P-T range of 940 °C–950 °C and 9.5–10.5 kbar, indicating ultra-high temperature (UHT) metamorphic overprinting. The subsequent retrograde metamorphic stage (M4) is characterized by Grt-r-Bt-Sil-Kfs-Pl-Qz ± Rt ± Ilm with symplectites of Bt-Sil-Qz in the garnet rim suggesting garnet breakdown with P-T conditions estimated as 770 °C–840 °C and 6.5–8 kbar. The pelitic granulites show a clockwise path, with P-T estimates higher than those in estimated in previous studies using conventional techniques. LA-ICP-MS U–Pb analysis of metamorphic zircon grains yield two groups of ages at 1972.9 ± 8.1 Ma and 1873.3 ± 9.9 Ma. We suggest that the protoliths of the Manjinggou HP-UHT granulites were deep subducted where they experienced HP metamorphism associated with the collision of the Ordos and Yinshan blocks at ca. 1.97 Ga. Subsequently, the UHT metamorphic overprint occurred during the assembly of the unified Western and Eastern Blocks of the NCC along the TNCO at ca. 1.87 Ga. Unlabelled Image • Ultra-high temperature metamorphic overprint on high pressure pelitic granulites • The UHT pelitic granulites record a T max metamorphic stage at 940 – 950 °C / 9.5 – 10.5 kbar. • Two groups of zircon U–Pb ages at 1973 and 1873 Ma correspond to the HP decompression and UHT cooling stages. • HP metamorphism refers to collision of Ordos and Yinshan blocks, UHT event to the assembly of Western and Eastern Blocks [ABSTRACT FROM AUTHOR]

The Cuonadong Dome in southern Tibet is a newly discovered gneiss dome in the Tethys Himalaya. Here, we investigate the Late Cambrian augen gneiss (orthogneiss) within the core of this dome to address the controversy surrounding early Palaeozoic tectonic evolution of the northern margin of eastern Gondwana. We report new zircon laser ablation multicollector inductively coupled plasma mass spectrometry (LA‐(MC‐)ICP‐MS) U‐Pb ages, Lu‐Hf isotopes, whole‐rock major and trace element geochemistry, and Sr‐Nd‐Pb data on representative samples from the granitic gneiss. The weighted mean of 116 analyses of zircon grains yields an age of 498.2 ± 1.5 Ma (mean square weighted deviation [MSWD] = 1.2). Forty‐one spots analyses on these grains show consistent εHf (t) values of −2 to +4 (average = +1.1), corresponding to Hf crustal model age (TDM2) of 1.3 to 1.6 Ga (average = 1.39 Ga). The orthogneiss (metagranite) is characterized by high Si and K contents, with low Al, Mg, and Ti, and A/CNK values ranging from 0.87 to 0.98 with an average of 0.92, indicating a metaluminous composition and I‐type granitoid affinity. The granitoid displays significant enrichment in light rare earth elements (LREEs) and relatively flat high rare earth element (HREE) patterns, with strong negative Eu anomalies (Eu/Eu* = 0.26–0.31). The primitive mantle‐normalized trace elements show a relative enrichment in large‐ion lithophile elements, such as Rb, and high‐field strength elements, such as Th, U, Zr, and Hf, with depletion in Ba, Nb, Ta, Sr, P, and Ti. The rocks show high initial 87Sr/86Sr ratios (0.7221–0.7248) and low εNd (t) values (−8.9 to −7.3) with Nd model ages (TDM) of 1.79–1.91 Ga. Their radiogenic Pb isotopic compositions show (206Pb/204Pb)t = 18.804–19.110, (207Pb/204Pb)t = 15.730–15.768, and (208Pb/204Pb)t = 38.409–39.054, indicating an ancient upper middle continental crustal origin. Our study shows that the protolith of the metagranite was most likely derived from the partial melting of upper continental crust with a minor contribution of depleted mantle materials. Through integration of the regional information on early Palaeozoic magmatism and metamorphic events, we contend that the protolith of the Cuonadong granitic gneiss formed in an accretionary setting associated with the early Palaeozoic Proto‐Tethys Oceanic plate subduction beneath the Gondwana continent. [ABSTRACT FROM AUTHOR]

Graphite in high grade meta-supracrustal rocks provide an important proxy to characterize biogenic and abiogenic carbon sources. Here we investigate graphite in various associations within the granulite facies metapelites (khondalites) of Kerala in southern India with a view to characterize the textural varieties and their genesis through the application of laser Raman spectroscopy and carbon isotopes. We trace the increasing intensity of metamorphism from the Raman spectra of the different graphite types. The δ13C values of the graphite show two distinct origins; the relatively lighter values in the range of −17.5‰ to −20.7‰ represent a mixture of biogenic and magmatic carbon, whereas the heavier isotopes in the range of −11.7‰ to −13.8‰ are suggested to present graphite precipitation from CO 2 -rich fluids from sub-crustal magmatic sources. Our study provides insights on the spectral properties of graphite in relation to the intensity of metamorphism and also reveals both biogenic and abiogenic sources of carbon. Unlabelled Image • Quantitative Raman spectra of graphite as indicators of increasing intensity of metamorphism • Graphite formation from both biogenic and abiogenic sources • Zircon U-Pb age dating of the host metapelite indicates protolith age of ca. 2061 Ma and high grade metamorphism at ca. 539 Ma. [ABSTRACT FROM AUTHOR]

This study presents zircon U–Pb ages and geochemical and Sr–Nd isotopic data for acid granites from the Uliastai continental margin, which is located in the Ulaan Tolgoi area of the south‐eastern Central Asian Orogenic Belt (CAOB). Although most samples have similar calc‐alkaline (K2O/Na2O = 0.55–1.70, average of 1.35) and peraluminous (A/CNK = 1.02–1.20 and A/NK = 1.09–1.87) characteristics, the granodiorites, monzogranites, and alkali feldspar granites exhibit distinct light rare earth element (LREE)/heavy REE (HREE) anomalies, including negative Nb, P, Ti, Sr, and Ba anomalies and negative εNd(t) values. These characteristics indicate that this complex massif comprises lower Early Carboniferous subduction‐related calc‐alkaline granodiorites (348 ± 1 Ma); an upper Early Carboniferous syn‐collisional segment characterized by S‐type, high‐K, calc‐alkaline, and peraluminous monzonitic granites (334 ± 1 Ma); and Late Carboniferous post‐orogenic extensional A2‐type peraluminous alkali feldspar granites (317 ± 1 Ma). Previous studies performed on coeval volcanic rocks and Early Palaeozoic granites in the same area have demonstrated that the Early Carboniferous granodiorites have the same geochemical characteristics as volcanic arc granites (VAGs), thus indicating that the northward subduction of the Hegenshan Ocean may have continued through the Early Carboniferous. The monzogranite and alkali feldspar granites, in conjunction with the Late Carboniferous lagged arc volcanic rocks observed in this area, suggest a syn‐collisional to post‐collisional setting. The new data presented in this study provide constraints on the timing of the transition from island‐arc magmatism to post‐collisional extension‐related magmatism in this region during the later stage of the Early Carboniferous. [ABSTRACT FROM AUTHOR]

Abstract The Helanshan tectonic belt (HTB) is a major tectonic divide between the Alxa and Ordos blocks in the North China Craton. The geochronology and petrogenesis of the mafic dykes in the northern HTB are keys to understanding the tectonic evolution of this belt. The mafic dykes, intruded into the Neoarchean–Paleoproterozoic metamorphic basement, are mainly composed of diabase with a mineral assemblage of plagioclase (45%–60%), pyroxene (25%–35%), minor quartz and Fe–Ti oxides. The LA-ICPMS U–Pb analysis of zircon grains from representative dykes yield a weighted mean age of 206 ± 1.9 Ma, which represents the crystallization age of the dyke. The diabases show high contents of Fe 2 O 3 T (11.88–17.55 wt.%), low contents of SiO 2 (45.65–50.95 wt.%) and MgO (3.31–5.50 wt.%) with low Mg# (=100 × MgO/(MgO + FeO) atomic ration) of 33–44. They are characterized by enrichment of light rare earth elements (LREEs) and large ion lithophile elements (LILEs) (e.g., Rb, Ba and Pb), and slight depletion of high field strength elements (HFSEs). These features suggest that the magma has undergone extensive fractionation of olivine and pyroxene but only minor crustal contamination during its evolution. Their high Sm contents and La/Sm ratios, and low Sm/Yb ratios indicate that magma from which the dykes formed was derived from low degree (about 5%) partial melting of an enriched garnet + spinel lherzolite mantle source. Together with regional geology, these geochemical and geochronological data suggest that the mafic dykes in the HTB were formed in an intracontinental extensional setting during the late Triassic. Graphical abstract Image 1 Highlights • Mafic dykes in the Helanshan Mountains have a crystallization age of 206 ± 1.9 Ma. • The dykes were derived from an enriched, lithospheric mantle source. • The dykes were formed in an intracontinental extensional setting in Late Triassic. [ABSTRACT FROM AUTHOR]

The recently discovered Diyanmiao ophiolite in the eastern part of the Erenhot-Hegenshan ophiolite belt forms part of the southeastern domain of the Central Asian Orogenic Belt (CAOB). The ophiolite suite is composed of the northern Baiyinbulage ophiolite and the southern Naolaiketu ophiolite, each extending for nearly 100 km, and a width of around 6 km. The suite preserves a well-exposed and a nearly-complete ophiolite stratigraphy, and includes, from bottom to top, harzburgite, bedded gabbro, isotropic gabbros, anorthosite, spilite, pillow basalt, keratophyre, baschtauite, with overlying chert, and plagiogranite veins locally intruding the pillow basalt and gabbro. The pillow basalts possess the geochemical characteristics of Hahajima island arc tholeiite (IAT), indicating that the Diyanmiao ophiolite formed in the incipient arc setting of the supra-subduction zone. LA-ICP-MS U-Pb dating of zircon grains from three gabbro samples yield ages of 361 ± 13 Ma, 356.7 ± 3.8 Ma and 340 ± 14 Ma, indicating an early-Carboniferous age for the Diyanmiao ophiolite. We suggest that the intra-oceanic subduction initiation of the Erenhot-Hegenshan paleo-ocean during the Early Carboniferous resulted in the formation of an incipient arc oceanic crust, and that the Diyanmiao ophiolite represents an important north-dipping subduction event of the paleo Asian oceanic crust beneath the southern margin of the Siberian Plate after Early Carboniferous and Early Permian. Our study provides further insights into the evolution of the Paleo-Asian Ocean and eventual construction of CAOB, the globe's largest Phanerozoic orogen. [ABSTRACT FROM AUTHOR]

The Lützow-Holm Complex (LHC) of East Antarctica has been regarded as a collage of Neoarchean (ca. 2.5 Ga), Paleoproterozoic (ca. 1.8 Ga), and Neoproterozoic (ca. 1.0 Ga) magmatic arcs which were amalgamated through the latest Neoproterozoic collisional events during the assembly of Gondwana supercontinent. Here, we report new geochronological data on detrital zircons in metasediments associated with the magmatic rocks from the LHC, and compare the age spectra with those in the adjacent terranes for evaluating the tectonic correlation of East Antarctica and Sri Lanka. Cores of detrital zircon grains with high Th/U ratio in eight metasediment samples can be subdivided into two dominant groups: (1) late Meso- to Neoproterozoic (1.1–0.63 Ga) zircons from the northeastern part of the LHC in Prince Olav Coast and northern Sôya Coast areas, and (2) dominantly Neoarchean to Paleoproterozoic (2.8–2.4 Ga) zircons from the southwestern part of the LHC in southern Lützow-Holm Bay area. The ca. 1.0 Ga and ca. 2.5 Ga magmatic suites in the LHC could be proximal provenances of the detrital zircons in the northeastern and southwestern LHC, respectively. Subordinate middle to late Mesoproterozoic (1.3–1.2 Ga) detrital zircons obtained from Akarui Point and Langhovde could have been derived from adjacent Gondwana fragments (e.g., Rayner Complex, Eastern Ghats Belt). Meso- to Neoproterozoic domains such as Vijayan and Wanni Complexes of Sri Lanka, the southern Madurai Block of southern India, and the central-western Madagascar could be alternative distal sources of the late Meso- to Neoproterozoic zircons. Paleo- to Mesoarchean domains in India, Africa, and Antarctica might also be distal sources for the minor ∼2.8 Ga detrital zircons from Skallevikshalsen. The detrital zircons from the Highland Complex of Sri Lanka show similar Neoarchean to Paleoproterozoic (ca. 2.5 Ga) and Neoproterozoic (ca. 1.0 Ga) ages, which are comparable with those of the LHC, suggesting that the two complexes might have formed under similar tectonic regimes. We consider that the Highland Complex and metasedimentary unit of the LHC formed a unified latest Neoproterozoic suture zone with a large block of northern LH–Vijayan Complex caught up as remnant of the ca. 1.0 Ga magmatic arc. [ABSTRACT FROM AUTHOR]

The Dhala structure in Central India has been a topic of global interest ever since the report of an ancient meteorite impact event there. Here we present an integrated study of the petrology, geochemistry, and zircon U-Pb zircon geochronology and rare earth element geochemistry from the structure along with and an analysis of the grain morphology and textural features. Our results provide new insight into the nature and timing of the impact event. The zircon grains from the impactites show textures typical of shock deformation which we correlate with the impact event. We also identified the presence of reidite based on Raman spectroscopy and characteristics such as a persistent planar fracture, bright backscattered electron images, and a lack of zoning, which are all diagnostic features of this mineral formed during an impact event. Our zircon U-Pb data from the various rock types in the basement show magma emplacement at ca. 2.5–2.47 Ga, and the Pb loss features suggest that the impact might have occurred between ca. 2.44 Ga and ca. 2.24 Ga. Another minor group of late Paleoproterozoic zircons with concordant ages of 1826 and 1767 Ma in the brecciated quartz reefs along the margins of the impact crater from unfractured grains represent an younger thermal event after the impact. The rare-earth element patterns of the Neoarchean to early Paleoproterozoic zircon population reflect the effects of hydrothermal alteration on a peralkaline host rock. The abnormally high concentration of K 2 O in the impactite (up to 15.91 wt%), is also consistent with metasomatic alteration associated with the impact event. [ABSTRACT FROM AUTHOR]

The Baoligaomiao Formation, within the Hegenshan ophiolite-arc-accretion complex is an important segment to understand the tectonic evolution of the Central Asian Orogenic Belt (CAOB), world's largest Phanerozoic orogenic belt. In this study, we present an integrated study of zircon U-Pb isotopic ages, whole rock major-trace elements, and Sr-Nd-Pb isotopic data from the volcanic succession in the Baoligaomiao Formation. The volcanic succession can be divided into the lower sequence with zircon U-Pb ages in the range of 326.3 Ma–307.4 Ma and the upper sequence of 305.3 Ma. The succession belongs to two suites: calc-alkaline volcanics and high-Si rhyolites. The calc-alkaline volcanic rocks include basaltic andesite through andesite and dacite to rhyolite and their pyroclastic equivalents. These rocks exhibit a well-defined compositional trend from basaltic to rhyolitic magma, reflecting continuous fractional crystallization. These rocks show obvious enrichment in LILEs and LREEs and relative depletion of HFSEs, typical of subduction-related magma. The calc-alkaline rocks have low initial 87 Sr/ 86 Sr (0.7023–0.7052), positive ɛNd(t) values (2.75–4.80), and their initial Pb isotopic compositions are 17.875–18.485 of 206 Pb/ 204 Pb, 15.481–15.520 of 207 Pb/ 204 Pb and 37.467–37.764 of 208 Pb/ 204 Pb, respectively. Geochemical and isotopic results suggest that the volcanic succession represents Carboniferous subduction-related, mature, continental arc volcanism. The outcrops of high-Si rhyolites are restricted to the northern edge of the continental arc, marking a transition zone between volcanic arc and back-arc basin, where they are interbedded with the calc-alkaline rocks in the lower sequence, and the upper sequence is composed only of high-Si rhyolites. The high-Si rhyolites have high SiO 2 (71.12–81.76 wt%) and varied total alkali contents (K 2 O + Na 2 O = 5.46–10.58 wt%), low TiO 2 (0.06–0.27 wt%), MgO (0.09–0.89 wt%) and CaO (0.08–0.72 wt%). Based on the presence of mafic alkali phenocrysts, such as arfvedsonite and siderophyllite, high Zr/Nb ratios (> 10) and peralkalinity index (PI) near unity, the high-Si rhyolites can be classified as peralkaline comendites. The high-Si rhyolites are characterized by unusually low Sr and Ba, and high abundance of Zr, Th, Nb, HREEs and Y. They show geochemical characteristics similar to those of typical A 2 -type granites including their high K 2 O + Na 2 O, Nb, Zr and Y, and high ratios of FeO T /MgO, Ga/Al and Y/Nb. Our study suggests that the high-Si rhyolites were derived from discrete trachytic parent magma with fractional crystallization within shallow magma reservoirs. Their Nd-Pb isotopic characteristics are similar to those of the calc-alkaline arc rocks and are compatible with partial melting of pre-existing juvenile continental arc crust. We observe that the widespread eruptions of A 2 -rhyolitic magmas (305.3 Ma–303.4 Ma) following a short period of magmatic quiescence was temporally and spatially associated with voluminous intrusion of the bimodal magmas (304.3 Ma–299.3 Ma) in the pre-existing arc volcanic-plutonic belt (329 Ma–307 Ma). We envisage northward subduction and slab breakoff process resulting in an obvious change of the regional stress field to extensional setting within the Carboniferous continental arc running E-W for thousands of kilometers. Therefore, we propose the existence of an east-west-trending Carboniferous continental arc in the Hegenshan ophiolite-arc-accretion complex, with the slab breakoff event suggesting that the age of the upper sequence (305.3 ± 5.5 Ma) likely indicates the maximum age for the cessation of the northward subduction of the Hegenshan oceanic lithosphere. [ABSTRACT FROM AUTHOR]

The NS-treading Zhongdian Arc located in the southern part of the Yidun Arc is an important region to address the evolution and reconstruction of the Palaeo-Tethys Ocean and related mineralization. In this study, we investigate three barren intrusions in the Zhongdian Arc and present geochemical compositions, zircon U–Pb dating and Hf isotopic compositions. Zircons from the three intrusions yielded U–Pb ages of ~227.5, ~222.5, and ~230 Ma, with highly variableεHf(t) values (‒20.5 to 4.3). These quartz monzonite porphyries show typical adakitic affinity, and it is inferred that these intrusions in the Zhongdian Arc, together with those in the northern Yidun Arc, were derived from the partial melting of mantle wedge and contaminated by minor lower crustal components during the westward subduction of the Ganzi-litang Ocean, which probably resulted from the Triassic continental collision between the south China and the north China blocks. In the Yidun Arc, the Triassic ore-bearing intrusions haveεHf(t) values that cluster around zero, while the barren intrusions possess negativeεHf(t) values, suggesting that the mantle lithospheric components played an important role in the Triassic ore-bearing porphyries. [ABSTRACT FROM AUTHOR]

The Fuping Complex is one of the important basement terranes within the central segment of the Trans-North China Orogen (TNCO) where mafic granulites are exposed as boudins within tonalite-trondhjemite-granodiorite ( TTG) gneisses. Garnet in these granulites shows compositional zoning with homogeneous cores formed in the peak metamorphic stage, surrounded by thin rims with an increase in almandine and decrease in grossular contents suggesting retrograde decompression and cooling. Petrological and phase equilibria studies including pseudosection calculation using thermocalc define a clockwise P-T path. The peak mineral assemblages comprise garnet+clinopyroxene+amphibole+quartz+plagioclase+K-feldspar+ilmenite±orthopyroxene±magnetite, with metamorphic P-T conditions estimated at 8.2-9.2 kbar, 870-882 °C (15 FP-02), 9.6-11.3 kbar, 855-870 °C (15 FP-03) and 9.7-10.5 kbar, 880-900 °C (15 FP-06) respectively. The pseudosections for the subsequent retrograde stages based on relatively higher H2O contents from P/T-M(H2O) diagrams define the retrograde P-T conditions of <6.1 kbar, <795 °C (15 FP-02), 5.6-5.8 kbar, <795 °C (15 FP-03), and <9 kbar, <865 °C (15 FP-06) respectively. Data from LA- ICP- MS zircon U-Pb dating show that the mafic dyke protoliths of the granulite were emplaced at c. 2327 Ma. The metamorphic zircon shows two groups of ages at 1.96-1.90 Ga (peak at 1.93-1.92 Ga) and 1.89-1.80 Ga (peak at 1.86-1.83 Ga), consistent with the two metamorphic events widely reported from different segments of the TNCO. The 1.93-1.92 Ga ages are considered to date the peak granulite facies metamorphism, whereas the 1.86-1.83 Ga ages are correlated with the retrograde event. Thus, the collisional assembly of the major crustal blocks in the North China Craton (NCC) might have occurred during 1.93-1.90 Ga, marking the final cratonization of the NCC. [ABSTRACT FROM AUTHOR]

The Trans-North China Orogen (TNCO) marks the major (ca. 300 km wide) Paleoproterozoic collisional suture between the Eastern and Western Blocks of the North China Craton (NCC), which also incorporates several microblocks or complexes. Here we investigate the Zanhuang Complex along the eastern margin of TNCO. We present petrological, geochemical, zircon U–Pb and Lu–Hf data on a suite of quartz-mica schist, metavolcanics and diorite from the Central Zanhuang Domain (CZD), as well as granitoids and amphibolite that constitute the basement rocks of the Western Zanhuang Domian (WZD) and Eastern Zanhuang Domain (EZD). Our study represents a cross section across two continental margins and covers the paleo-ocean tract in between. The metavolcanics show calc-alkaline to tholeiitic affinity, and negative correlations of (La/Sm) N vs. P/Nd, Ti/Ti ∗ , Ce/Ce ∗ , and positive with Nb/Nb ∗ . The granitoids fall within the VAG field. The IAB and MORB features of the volcanic suite are consistent with magma derivation in arc to back arc environment from an enrichment source. The magmatic suite also displays LREE enrichment, positive Rb, K, La, Pb, Nd anomalies and negative Ta, Nb, Ce, Ti anomalies. LA-CIPMS U–Pb geochronology of detrital zircon grains shows two age populations in the quartz-mica schist with 207 Pb/ 206 Pb mean ages of 2499 ± 14 Ma, and 2252 ± 22–2216 ± 39 Ma, and the timing of deposition is estimated as ca. 2.3–2.2 Ga. Zircons from the granodioritic gneiss yield 207 Pb/ 206 Pb mean age of 2508 ± 14 Ma, representing Neoarchean continental basement. The metavolcanics and two diorite samples yield ages of 2302 ± 30 Ma, 2089 ± 63 Ma marking the timing of an active arc. The metamorphic zircons from these rocks show an age of 1882 ± 15 Ma. The zircon Lu–Hf data yield both positive and negative εHf(t) values, suggesting depleted mantle source mixed with crustal components. Their crustal residence ages ( T DM C ) range from 3875 to 2224 Ma and depleted model ages ( T DM ) range from 3415 to 2092 Ma suggesting mixed juvenile and reworked crustal components and possible vestiges of Mesoarchean basement. We propose that the Zanhuang Complex is one of the Paleoproterozoic arcs within the TNCO which was accreted to the Neoarchean continent along the Eastern Block of the NCC during the suturing along the TNCO. The tectonics associated with crustal growth and recycling in the TNCO and the arc-continent collision broadly coincided with the building of the Columbia supercontinent. [ABSTRACT FROM AUTHOR]

Metamorphic regimes in Archean terranes provide important keys to the plate tectonic processes in early Earth. The North China Craton (NCC) is one of the ancient continental nuclei in Asia and recent models propose that the cratonic architecture was built through the assembly of several Archean microcontinental blocks into larger crustal blocks. Here we investigate garnet- and pyroxene-bearing granulite facies rocks along the periphery of the Jiaoliao microcontinental block in the NCC. The garnet-bearing granulites contain peak mineral assemblage of garnet + clinopyroxene + orthopyroxene + magnetite + plagioclase + quartz ± biotite ± ilmenite. Mineral phase equilibria computations using pseudosection and geothermobarometry suggest peak P – T condition of 800–830 °C and 7–8 kbar for metamorphism. Isopleths using X Mg of orthopyroxene and X Ca of garnet in another sample containing the peak mineral assemblage of garnet + orthopyroxene + quartz + magnetite ± fluid yield peak P – T conditions of 860–920 °C and 11–14 kbar. Geochemical data show tonalitic to granodioritic composition and arc-related tectonic setting for the magmatic protoliths of these rocks. Zircon LA-ICP-MS analyses yield well-defined discordia with upper intercept ages of 2562 ± 20 Ma (MSWD = 0.94) and 2539 ± 21 Ma (MSWD = 0.59) which is correlated with the timing of emplacement of the magmatic protolith. A younger group of zircons with upper intercept ages of 2449 ± 41 Ma (MSWD = 0.83); N = 6 as 2449 ± 41 Ma (MSWD = 0.83; N = 6) and 2480 ± 44 Ma (MSWD = 1.2; N = 9) constrains the timing of metamorphism. Zircon Lu–Hf data show dominantly positive εHf(t) values (up to 8.5), and yield crustal residence ages (T DM C ) in the range of 2529 to 2884 Ma, suggesting magma sources from Meso-Neoarchean juvenile components. The high temperature and medium to high pressure metamorphism is considered to have resulted from the subduction–collision tectonics associated with microblock amalgamation in the NCC at the end of Archean. Together with the evidence for high pressure metamorphism from an adjacent locality, our results correlate with models that predict paired metamorphism at the Archean–Proterozoic transition with the onset of modern style plate tectonics. [ABSTRACT FROM AUTHOR]

The Trans-North China Orogen (TNCO) represents one of the major Paleoproterozoic collisional orogens across the central part of the North China Craton. Here we investigate the meta-carbonates (marbles and calc-silicate rocks) from the Fuping and Zanhuang Complexes in the TNCO through a combination of detrital zircon U–Pb geochronology, geochemistry and stable isotopes (carbon and oxygen). The U–Pb ages obtained from detrital zircons in both sequences show age populations of 2.50–2.57 Ga, 2.2–2.4 Ga, 2.0–2.1 Ga and 1.85–1.90 Ga. The depositional age for the Wanzi Group in the Fuping Complex is further constrained as 1.95–1.93 Ga and the Central Zanhuang Domain (Zanhuang Complex) as 2.03–1.90 Ga. All samples show nearly flat REE patterns below the concentration level of 1 in the shale-normalized REE distribution diagram. The dolomite–calcite marbles from the Fuping Complex have δ 13 C values ranging from −0.31‰ to 3.65‰ and δ 18 O values vary from −9.12‰ to −2.96‰. The calc-silicate rocks from the Fuping Complex show wide variation of δ 13 C (−1.56‰ to 3.30‰) and δ 18 O (−12.89‰ to −5.84‰). Dolomite marbles from the Zanhuang Complex show low δ 13 C and δ 18 O values ranging from −3.31‰ to −3.69‰ and −12.98‰ to −13.59‰. The dolomite–calcite marbles from the Zanhuang Complex display δ 13 C and δ 18 O compositions of −2.68‰ to 1.44‰ and −11.77‰ to −7.76‰, respectively. The correlations between the isotopic results (δ 13 C and δ 18 O) and geochemical compositions (Mn, Sr, Mn/Sr, Mg/Ca, Ca/Sr and Fe/Sr) suggest that the dolomite marbles from the Zanhuang Complex are strongly disturbed and the calc-silicate rocks are moderately affected by the post-depositional processes. The salient lithological, geochemical and isotopic features imply that the protoliths of the meta-carbonates were formed in a proximal and shallow marine environment. The Wanzi Group was deposited in a forearc basin and the Central Zanhuang Domain was formed in a back-arc basin. The geochemical imprints and biospheres of the oceanic basin in the Fuping area were possibly affected by the Lomagundi or Jatulian Event, resulting in the positive excursion of δ 13 C values in the dolomite–calcite marbles. However, the back-arc basin in the Zanhuang area was formed after the 2.1–2.0 Ga rifting event, thus it was generated after the Jatulian Event, thus preserving normal δ 13 C values of marine carbonates. [ABSTRACT FROM AUTHOR]

The Gangdese magmatic belt, located in the southern margin of the Lhasa terrane and carrying significant copper and polymetallic mineralization, preserves important information relating to the tectonics associated with Indian–Eurasian collision and the crustal growth of southern Tibet. Here we investigate the Quxu batholith in the central domain of the Gangdese magmatic belt and report the occurrence of hornblende gabbros for the first time. We present petrologic, zircon U–Pb–Hf isotopic and bulk-rock chemistry data on these rocks. The hornblende gabbros display sub-alkaline features, and correspond to tholeiite composition. They also show medium K calc-alkaline to low K affinity. The rocks show enrichment in LILEs and LREEs, but are depleted in HFSEs, indicating a subduction-related active continental margin setting for the magma genesis. Our computations show that the gabbroic pluton was emplaced in the middle-lower crustal depth of ca. 18 km. Zircons from the hornblende gabbros yield crystallization age of ca. 210 Ma, revealing a late Triassic magmatic event. Combined with available data from the Gangdese magmatic belt, our study suggests that the northward subduction of the Neo-Tethys oceanic crust beneath the southern margin of the Lhasa terrane might have been initiated not later than the Norian period of Triassic. Zircons from the hornblende gabbro show positive ε Hf (t) values of 9.56 to 14.75 (mean value 12.44), corresponding to single stage model ages (T DM1 ) in the range of 256 Ma to 459 Ma, attesting to crustal growth in the southern Lhasa terrane associated with the subduction of the Neo-Tethys oceanic crust. [ABSTRACT FROM AUTHOR]

The stratabound Tianhu iron deposit, with a reserve of 104 Mt at 42% Fe, is located in the eastern part of the Central Tianshan zone in the southern part of the Central Asian Orogenic Belt. The deposit hosts schist, quartzite, marble, amphibolite, and granitic gneiss belonging to the Tianhu Group. Laser ablation inductively coupled plasma mass spectrometry was used to perform zircon U–Pb geochronology, bulk-rock geochemistry, andin situzircon Hf isotope analyses of the metavolcanic host rocks for constraining the timing and genesis of the Tianhu iron deposit. According to the newly determined age constraints of 452 ± 3 and 477 ± 4 Ma, the iron deposit was concluded to be Ordovician in age. Geochemistry and zircon Lu–Hf isotope analyses suggested that the host rocks of the deposit represent metamorphosed arc-type volcanic rocks generated by the partial melting of a lower crustal source. Combined with geological and ore petrographic characteristics, the Tianhu iron deposit is interpreted to be of volcano–sedimentary origin with enrichment during subsequent metamorphism. The early Palaeozoic marks a critical iron mineralization epoch in the Eastern Tianshan area. The results also support the model of the Central Tianshan area as a volcanic-arc during the early Palaeozoic, associated with the subduction of the Northern Tianshan Ocean. [ABSTRACT FROM AUTHOR]

The mid-Neoproterozoic medium- to high-K calc-alkaline magmatic rocks in the northeastern margin of the Indochina block, SW China, provide important insights into the relationship of the Indochina block with the Gondwana supercontinent. Here we report zircon LA-ICP-MS U–Pb data from the early and late stage plutons which yield weighted mean 206 Pb/ 238 U ages of 765 Ma and 732–739 Ma suggesting mid-Neoproterozoic emplacement. The zircon ε Hf ( t ) values show a range of − 3.2 to + 2.4 (average + 0.1 ± 0.9) with T DM C of 1510 to 1870 Ma for the early plutons, and − 5.4 to + 5.1 (average + 2.1 to − 3.9) with T DM C of 1366 to 1985 Ma for late plutons. Both groups show similar geochemical characteristics including high Mg # , enrichment of LILE and LREE, slight negative Eu anomalies, and strongly negative Nb, Ta and Ti anomalies, with all the samples falling within the continental/island arc field in tectonic discrimination diagrams. These features suggest that the early and late stage magmas were produced by the mixing of mantle-derived magma and crust-derived magma in different proportion within an active continental margin, in subduction-related continental-arc tectonic setting. The linear zoning and roughly parallel distribution of the two generations of intrusions with a hiatus of 20 Ma might suggest an episode of ridge subduction with asthenosphere upwelling through the slab window that generated the second phase of plutons. [ABSTRACT FROM AUTHOR]

The Fuping, Wutai, and Hengshan Complexes in the North China Craton preserve imprints of widespread late Neoarchean magmatism. Here, we report results from systematic petrology, mineral chemistry, whole-rock major, trace and platinum-group element geochemistry, zircon U–Pb geochronology and Hf–O isotopes from the Yangmuqiao mafic–ultramafic intrusion and coeval tonalite–trondhjemite–granodiorite (TTG) gneiss from the Fuping Complex. The mafic–ultramafic intrusion is composed of pyroxene hornblendites, hornblendites, and minor harzburgites. The salient geochemical features of the mafic–ultramafic intrusion and the Fuping TTG gneiss display subduction-related island arc signature, such as fractionated REE patterns with elevated LREE, enrichment of LILE (K, Rb, and Ba) and LREE (La and Ce), and depletion of HFSE (Nb, Ta, Zr, and Hf) and HREE. The chemistry of the clinopyroxene and chromite in the pyroxene hornblendites shows affinity with Alaskan-type mafic–ultramafic intrusions. Zircons from the pyroxene hornblendite yield weighted mean 207 Pb/ 206 Pb age of 2514 ± 15 Ma, and those in the Fuping TTG gneiss show mean age of 2513 ± 13 Ma. Zircon Hf and O isotopic compositions are used as magma source and crustal evolution indicators. Zircon grains in the pyroxene hornblendite display positive ε Hf (t) values (2.6–6.7), Neoarchean T DM (2570–2723 Ma), and their δ 18 O values vary from 3.8‰ to 7.0‰ (average 6.2‰). Zircons in the TTG gneiss show ε Hf (t) values in the range of − 1.8 to 4.9, T DM of 2637–2888 Ma, and δ 18 O values of 4.1‰–6.7‰ (average of 6.1‰). These results suggest that the parental magma of the late Neoarchean magmatism in the Fuping area was dominantly extracted from the depleted mantle and contaminated to different degrees by crustal components. The pyroxene hornblendites have obviously higher IPGE contents (ΣIPGE = 1.69–2.39 ppb) and lower Pd/Ir ratios (5.97–6.28) than those in the hornblendites (ΣIPGE = 0.56–0.72 ppb, Pd/Ir = 6.48–15.25), suggesting different compatibility of IPGE and PPGE during the fractional crystallization. The study area is located at the western segment of the Fuping Complex and the eastern periphery of the Wutai greenstone belt. We propose that the late Neoarchean arc magmatism recorded by the Yangmuqiao mafic–ultramafic intrusion and the Fuping TTG gneiss is related to the subduction–collision process of the Ordos and the Qianhuai microblocks along the zone of ocean closure represented by the Wutai greenstone belt. [ABSTRACT FROM AUTHOR]

The Archaean Earth is considered to have been characterized by microcontinents that formed, dominantly, through the accretion of oceanic arcs and plateaus. The North China Craton (NCC) provides a typical case where at least seven ancient microcontinental nuclei with distinct lithological features and independent tectonic histories were amalgamated into the cratonic framework at the end of the Archaean. Here we investigate a suite of magmatic rocks developed at the periphery of one of these microblocks, the Jiaoliao Block that forms part of the composite Eastern Block of the NCC. We present petrological, geochemical and zircon U–Pb geochronological data from the Taipingzhai charnockite suite, and associated amphibolites, metagabbros and orthogneisses from the Qianxi Complex. Geochemically the rocks show a wide range of SiO 2 (charnockite suite: 52.57–75.50 wt.%; metagabbro: 43.71 wt.%; amphibolite: 50.24 wt.%; garnet-bearing biotite: 63.73 wt.%), and MgO (charnockite suite: 0.89–5.01 wt.%; metagabbro: 3.99 wt.%; amphibolite: 6.23 wt.%; garnet-bearing biotite: 2.08 wt.%). The composition of the felsic units straddle from diorite through syeno-diorite to granite with both alkalic and subalkalic affinity, with dominantly magnesian composition and arc-related features. Their immobile trace element relationships suggest calc-alkaline affinity. They show positive Pb, Ba, La, Nd, and Gd and negative Nb, Ta, Sr, Th and Ti anomalies with slightly negative anomalies of Ce and Y, attesting to arc-related features. In tectonic classification diagrams, the rocks plot in the VAG + syn-COLG field or the VAG area suggesting subduction-related origin. The dominant population of zircons in all these rocks displays magmatic crystallization features including high Th/U values with core-rims textures indicating subsequent thermal events. The zircon U–Pb data yield upper intercept ages of 2587 ± 10 Ma to 2543 ± 17 Ma and 207 Pb/ 206 Pb mean ages of 2578 ± 7.3 Ma to 2536 ± 8 Ma for the charnockite suite, marking the timing of emplacement of the arc magmas. The overgrowth rims as well as discrete neoformed grains are interpreted as dating subsequent metamorphism and yield 207 Pb/ 206 Pb ages between 2533 Ma to 2490 Ma. Zircons in the metagabbro preserve upper intercept ages of 2556 ± 20 Ma representing the crystallization age of this rock. The younger ages of 2449 ± 58 Ma (upper intercept age) and 1845 ± 25 Ma ( 207 Pb/ 206 Pb spot age) are interpreted to represent subsequent multiple thermal events in this area. Zircons in the amphibolite preserve the 207 Pb/ 206 Pb mean age of 2539 ± 9 Ma, representing the crystallization age of this rock. The garnet-bearing biotite gneiss shows an upper intercept age of 2562 ± 10 Ma (MSWD = 0.66; N = 36) and the 207 Pb/ 206 Pb mean age of 2561 ± 9 Ma (MSWD = 0.63; N = 33) which is taken to represent the crystallization age of this rock. Some inherited zircons are also identified with 207 Pb/ 206 Pb ages of 2664 ± 26 Ma and 2628 ± 26 Ma. Zircon Lu–Hf data show dominantly positive εHf(t) values and combined with crustal residence ages, the results suggest Mesoarchean to Neoarchean juvenile crust formation in the NCC. We interpret the data presented here to represent a phase of major late Neoarchaean arc magmatism along the western margin of the Jiaoliao Block related to the birth of microcontinental nuclei within the NCC. Our data suggest that the Western and Eastern Blocks might not have existed as discrete crustal blocks, and that the construction of the NCC is a result of the assembly of several microblocks or terranes at the end of Archaean. Similar Archean cratonic nuclei in other regions of the world might have formed part of a primitive supercontinent in the early Earth. [ABSTRACT FROM AUTHOR]

The evolution of continental crust during Hadean and Archean and related geodynamic processes provides important clues to understand the early Earth history. Here we report evidence for Hadean and Eoarchean crust from the fringe of the Coorg Block, one of the oldest crustal blocks in Peninsular India. We present geological, petrological, and geochemical data, together with zircon U–Pb ages and Lu–Hf isotopes from a suite of metaigneous (granitoids, diorite, charnockite, metavolcanics) and metasedimentary (quartz mica schist, calcareous schist, ferruginous quartzite and BIF) rocks. Petrological and geochemical studies indicate that the igneous suite formed from subduction-related arc magmatism, and that the sedimentary suite represents an imbricated accretionary package of continental shelf sequence and pelagic components. Mineral thermometry suggests metamorphism under temperatures of 710–730 °C and pressures up to 8 kbar. Magmatic zircons in the metaigneous suite show oscillatory zoning and high Th/U contents (up to 3.72) and record multiple pulses of magmatism at ca. 3.5, 3.2, 2.7 and 2.5–2.4 Ga. The metasedimentary rocks accreted along the margins of the Coorg Block show multiple zircon population with mean 207 Pb/ 206 Pb ages at 3.4, 3.2, 3.1, 2.9, 2.7, 2.6, 2.5, 2.2, 2.0, and 1.3 Ga, and overprinted by younger thermal event at ca. 0.8–0.7 Ga. Zircons in the 3.5 Ga dioritic gneiss show positive εHf (t) values ranging from 0.0 to 4.2 and Hf crustal model ages (T DM C ) of 3517 to 3658 Ma suggesting that the parent magma was derived from Eoarchean juvenile sources. The zircons in the 3.2 Ga charnockite display εHf (t) values in the range of − 3.0 to 2.9 and Hf crustal model ages (T DM C ) of 3345 to 3699 Ma. The Neoarchean metagranites, diorites and felsic tuff show both positive and negative εHf (t) values and a range of T DM C values from 2904 to 3609 Ma suggesting magma derivation from Meso- to Eoarchean juvenile and reworked components. The T DM C values of the dominant zircon population in the metasedimentary suite range from 3126 to 3786 Ma, with the oldest value (4031 Ma) recorded by zircon grain in a ferruginous quartzite. The εHf (t) values of detrital zircons also show both positive and negative values, with a dominant crustal source. Our zircon U–Pb and Lu–Hf data suggest vestiges of Neohadean primordial continental crust in Peninsular India with episodic crustal growth during Eoarchean, Mesoarchean and Neoarchean building the continental nuclei. The results contribute to the understanding of crustal evolution in the early history of the Earth. [ABSTRACT FROM AUTHOR]

Extensive magmatism along convergent margin settings marks the late Neoarchean tectonics in the northern segment of the Southern Granulite Terrane (SGT) in Peninsular India. Here we investigate a suite of magmatic rocks (tonalite–trondhjemite–granodiorite [TTG], charnockite and amphibolite) together with accreted banded iron formation (BIF) from the western margin of the Nilgiri Block. The petrologic features of these rocks including the presence of primary amphiboles in all cases suggest crystallization from calc-alkaline magmas, typical of those derived from slab melting. The zircon grains in all the rock types investigated in this study show clear magmatic features including well-crystallized prismatic form, oscillatory zoning and high Th/U values. Zircons from two TTG gneiss samples show identical 207 Pb/ 206 Pb mean ages of 2521 ± 13 Ma and 2522 ± 17 Ma. Those from amphibolites display 207 Pb/ 206 Pb mean ages of 2590 ± 13 Ma and 2470 ± 17 Ma, with the cores of some grains preserving 2.6 Ga ages. Zircon grains from the charnockite yield 207 Pb/ 206 Pb mean age of 2601 ± 25 Ma whereas a single grain from the BIF shows 207 Pb/ 206 Pb age of 2493 ± 17 Ma. The age data converge to indicate late Neoarchean magmatism between ca. 2.6 and 2.5 Ga. The Lu–Hf isotope data on zircons from the rocks show positive εHf ( t ) values ranging from 2.3 to 9.3. The remarkably consistent and positive εHf ( t ) values suggest magma derivation from juvenile components, with no significant crustal participation. The mean T DM C values of zircons fall between 2674 and 2815 Ma, with the oldest at 2913 Ma, suggesting Meso- to Neoarchean juvenile components in the magma source. Our data indicate major crustal building events in the late Archean similar to those reported globally from other regions. The magmatism was a manifestation of melt generation along multiple subduction zones that assembled continental blocks into coherent cratonic architecture in southern India. [ABSTRACT FROM AUTHOR]

The Qinling orogenic belt preserves the records of a long evolution history of convergence between the North China Craton and the South China Craton. In this study, we present results from new geological, geochemical, zircon U–Pb geochronological and Lu–Hf isotopic investigations on a suite of orthogneisses from the Taihua Group (THG) and Tietonggou Group (TGG). We also present geochronological data on schist and migmatite from the North Qinling belt (NQB) and metasedimentary rocks from the Wuguan unit (WGU) which is exposed along the southern side of the Shangdan suture zone. Two orthogneisses from the THG define several stages of arc magmatism at ∼2.51 Ga, ∼2.34 Ga, ∼2.28 Ga and ∼2.16 Ga, followed by metamorphism at 1930 ± 31 Ma. Zircons from the TGG trace a tectonothermal event at 1897 ± 15 Ma. Geochemical data on biotite gneiss from the THG and the TTG (tonalite–trondhjemite–granodiorite) gneiss from the TGG classify these rocks as dacite and display volcanic arc affinity. Zircon Lu–Hf isotopic results suggest that the parental magma for the protolith of felsic gneisses were derived from Mesoarchean crustal components ( T DM C = 2766–3067 Ma). The amphibole gneiss from the THG classifies as metabasalt and the zircons from this rock show dominantly negative ε Hf ( t ) values varying from −10.3 to −4.6 and T DM C range of 3088–3437 Ma, suggesting magma derivation by melting of Paleoarchean–Mesoarchean subducted oceanic crust. Zircons in the schist from the NQB show a wide age population in the range of 937–1131 Ma (peak at 1035 Ma). Zircons from the melanosomes of the migmatite in the NQB define ages between 405 and 379 Ma, correlating with the melting event in the NQB during 450–380 Ma. The WGU shows age populations of 854–803 Ma (with a peak at 829–824 Ma), ∼2460 Ma, ∼1802 Ma and 1180–1000 Ma, which are markedly different from that of the NQB and SQB. The ages obtained in our study correlate with the widely reported Grenvillian-aged magmatism in the NQB, and suggest that the NQB might have been a discrete micro-continent during Paleo- and Mesoproterozoic which has been overprinted by Paleozoic tectonic event. [ABSTRACT FROM AUTHOR]

The Fuping Complex is exposed at the central domain of the Trans-North China Orogen (TNCO). Here we report new zircon LA-ICP-MS U–Pb ages, Lu–Hf isotope data, and whole rock geochemistry on a suite of meta-granitoids, amphibolites and metasedimentary rocks from the Fuping Complex. Magmatic zircons from the gneissic granite and syenogranites yield weighted mean 207 Pb/ 206 Pb ages of 2050 ± 21 Ma and 2077 ± 16 Ma, respectively. Those in two amphibolites show weighted mean 207 Pb/ 206 Pb ages of 2054 ± 26 Ma and 2044 ± 61 Ma. Zircons in a felsic schist define two age populations of 2450–2585 Ga and 2004–2097 Ga, suggesting the Fuping TTG gneisses and Nanying gneissic granites as the provenance. Our data also indicate that the Wanzi supracrustal sequence was deposited between 1.95 and 1.84 Ga. The geochemical data suggest that the 2.1–2.0 Ga granitic rocks and amphibolites from the Fuping Complex formed in subduction-related arc setting. The granitoids show SiO 2 content between 72.53 and 77.67 wt.% and classify as high-K shoshonitic, calc-alkalic to alkali granite. The amphibolites are subalkaline basalts in composition. Zircons from the 2.1–2.0 Ga granitoids and amphibolites display positive ɛ Hf ( t ) values in the range of 0.3–8.5 and Hf crustal model ages ( T DM C ) from 2124 to 2639 Ma. The 2.1–2.0 Ga magmatic zircons in the Wanzi supracrustal assemblage show relatively lower ɛ Hf ( t ) values (−0.8 to −2.6) and Hf crustal model ages ( T DM C ) of 2710–2801 Ma, suggesting that the magma sources of the 2.1–2.0 Ga suite included reworked 2.7–2.8 Ga crustal basement together with Neoarchean–Paleoproterozoic juvenile components. Based on the widespread 2.1–2.0 Ga magmatism as recorded in different rock types within the TNCO, we propose a tectonic model where we envisage simultaneous subduction and continental rifting process between several micro-blocks (or complexes). During 2.1–2.0 Ga, the Wutai Complex and the Fuping Complex were separated by the Longquanguan ocean. The double-sided subduction of the Longquanguan oceanic lithosphere resulted in distinct arc magmatism. Continental rift setting developed in the Hengshan, Huai’an and Zanhuang Complexes coevally. Finally, metamorphism associated with the ∼1.85 Ga collision between the Western Block and the Eastern Block along the TNCO overprinted all the lithologies. The Paleoproterozoic continent building recorded in this study correlates with similar events in the crustal fragments of the Columbia supercontinent. [ABSTRACT FROM AUTHOR]

The Cathaysia block records a complex tectonic history, the understanding of which is central to the debate on the evolution of the South China Block and its position in various supercontinent assemblies. Here we investigate two key formations from this block, the Mayuan Group in the northern Fujian Province, northeastern Cathaysia block and its equivalent the Badu Group in southwestern Zhejiang Province. Previous studies traced the Paleoproterozoic records from the Badu Group whereas a Neoproterozoic age was proposed for the Mayuan Group. The rocks sampled in this study from both groups show similar mineral assemblages of garnet + sillimanite + biotite + plagioclase + quartz ± K-feldspar ± muscovite ± graphite as well as high contents of SiO 2 and Al 2 O 3 , typical of amphibolite- to granulite-facies metapelitic rocks. Zircon U–Pb data yield two discordia intercept ages of ~ 1990 Ma and ~ 2450 Ma from one sample and discordia intercept ages of ~ 3.5 Ga, 2.5 Ga, 1.86 Ga and 233 Ma from another in the Badu Group. Zircons in two samples from the Mayuan group yield intercept ages of 1859 Ma and 249 Ma in one sample and ~ 2.6 Ga, 1.87 Ga, 257 Ma and a weighted mean 206 Pb/ 238 U age of 248 Ma in the other. The ca. 1.86–1.87 Ga and 230–250 Ma ages are interpreted to represent the time of metamorphic reworking because zircon grains of these ages tend to have low Th/U ratios, flat HREE patterns and unzoned internal texture as revealed by cathodoluminescene (CL) images. These results confirm that the Badu Group is a Paleoproterozoic lithostratigraphic unit and also suggest that at least part, if not all, of the Mayuan Group is Paleoproterozoic. Evidence for Paleozoic metamorphic reworking that is considered to have affected the whole of Cathaysia block is not revealed in this study; in contrast our data clearly show obvious Mesozoic metamorphic reworking at ca. 230–250 Ma. Zircon ɛ Hf (t) values range from − 19 to + 11 with a peak at − 5.5 and show T DM C (Hf) ranging from 1.9 to 4.1 Ga with a peak at ca. 2.7–3.0 Ga suggesting that a major crustal growth took place during this time. This interpretation is consistent with the previously suggested crustal growth peaks of ~ 2.7 Ga and ~ 2.9Ga. A synthesis of the reliable geochronological data gathered so far on Phanerozoic metamorphic reworking of the northeastern Cathaysia block reveals that the imprints of these tectonothermal events is differently distributed in the different zones. Rocks metamorphosed during the Paleozoic tectonothermal event dominantly occur in the western zone whereas those reworked by high-grade metamorphism during the Mesozoic tectonothermal event mainly outcrop in the eastern zone. Our study alerts the previous notion of a uniform distribution of the reworked rocks by high-grade metamorphism all across the northeastern Cathaysia block and provides new insights on the evolution of the South China Block. [ABSTRACT FROM AUTHOR]

Arc magmatism in convergent plate margins has been a major contributor to continental growth. Following arc–arc and arc–continent collisions in the Archean leading to the amalgamation of micro-blocks, the North China Craton (NCC) witnessed major pulses of continental arc magmatism during the Paleoproterozoic. In this study, we present geochemistry, zircon U–Pb geochronology and Lu–Hf isotope data from a suite of magmatic rocks sampled from the region of confluence of two major Paleoproterozoic suture zones in the NCC — the Inner Mongolia Suture Zone (IMSZ) and the Trans-North China Orogen (TNCO). Our zircon U–Pb geochronological data indicate new zircon growth during multiple tectonothermal events as displayed in the 207 Pb/ 206 Pb weighted mean ages of 2410 ± 41 Ma for metagranite, 2480 ± 12 Ma, 2125 ± 18 Ma, 1946 ± 8 Ma, 1900 ± 15 Ma and 1879 ± 12 Ma from metagabbros, 2446 ± 11 Ma from charnockite, and 1904 ± 6 Ma and 1901 ± 9 Ma from metatuffs. The 207 Pb/ 206 Pb upper intercept age of zircons in the khondalite shows 2102 ± 76 Ma which is identical to the age obtained from the magmatic zircons in one of the metagabbros. The khondalites also carry a group of concordant metamorphic zircons with 207 Pb/ 206 Pb mean age of 1881 ± 20 Ma. Metamorphic zircons in the gabbros and charnockites also yield similar ages of 1890 ± 14 Ma and 1852 ± 19 Ma respectively. The age data suggest prolonged arc magmatism in a convergent margin setting during ca. 2.48 to 1.9 Ga, followed by metamorphism at ca. 1.89–1.85 Ga associated with the final collision. Lu–Hf analyses reveal that the dominant populations of zircons from all the rock types are characterized by positive εHf values (− 1.9 to 6.8; mean 1.8). The εHf and T DM C data suggest that the magmas were mostly derived from Neoarchean and Paleoproterozoic juvenile components. The salient geochemical features of these rocks attest to magma generation from heterogeneous sources involving subduction-derived arc components with minor input from continental crust. The results presented in this study, together with those from previous investigations in different domains of the IMSZ and TNCO suggest major Paleoproterozoic arc magmatic events in the NCC lasting for nearly 600 million years associated with the final assembly of the crustal blocks into a coherent craton. Construction of the final cratonic architecture of the NCC thus witnessed not only the arc–continent amalgamations at 2.7–2.5 Ga, but also major crust building events in the Paleoproterozoic through melts generated from juvenile and recycled components in continental magmatic arc systems along an active convergent margin, followed by intense deformation and metamorphism during the final collision at 1.85–1.80 Ga. The prominent Paleoproterozoic magmatic records in the NCC do not support the proposal of global plate tectonic shutdown in the Siderian and confirm vigorous convergent margin magmatism and crust building processes throughout the Paleoproterozoic. [ABSTRACT FROM AUTHOR]

The multiphase emplacements of granitoids and well-developed depositional sequences from Neoproterozoic to Mesozoic are exposed widely in the Wugongshan domain of South China provide important keys for the reconstruction of the pre-Mesozoic tectonic evolution of the Cathaysia Block. Here we present the results from geological investigations, detrital zircon U–Pb geochronology, in situ Hf-isotope and REE composition of the Ordovician meta-sandstones, together with the U–Pb age data on a Mesozoic pluton with an attempt to evaluate the petrogenesis and crustal evolution history. A group of 276 detrital zircon U–Pb ages are reported from four meta-sandstones which show five major age populations: 2630–2350 Ma with a peak of 2440 Ma, 1890–1540 Ma (peak of 1680 Ma), 1120–870 Ma (peak of 980 Ma), 810–700 Ma (peak of 760 Ma) and 660–510 Ma (peak of 550 Ma). Among these, the most prominent age at 980 Ma fits well with the collisional event of Yangtze and Cathaysia Blocks. The second prominent age at 760 Ma correlates with a breakup of Rodinia, and the third one at 1680 Ma corresponds to the initial breakup of Columbia. For the fourth (peak of 2440 Ma) and fifth (peak of 550 Ma) ages, no corresponding magmatic rocks are exposed in the study area or in the adjacent regions, although the age populations broadly correspond to the global continental growth in the early Paleoproterozoic and the latest Neoproterozoic ‘Pan-African’ orogeny. We obtained 132 in situ Hf isotope compositions, among which 98 show negative εHf(t) values (− 36.88 to − 0.3) with two-stage model ages (T DM2 ) of 3.5–1.7 Ga (peak of 2.2 Ga), and 34 display positive εHf(t) values (+ 0.3 to + 9.89) with crystallization ages of 1.5–1.1 Ga (peak of 1.4 Ga). Zircons from two Mesozoic granitic samples yield rather similar late Jurassic ages of 158.1 ± 2.1 Ma and 154.0 ± 3.9 Ma. All the corresponding εHf(t) values of zircons are negative (− 24.2 to − 4.2) and the Hf two-stage model ages range from 1.5 to 3.0 Ga with a peak of 1.68 Ga. Combined with previous age data on 120 Ma massive granitoids and 230 Ma on ductile sheared plutons, we consider that the magmatism in the Wugong complex started from the late Triassic, and reached a peak in the late Jurassic, but was gradually weakened since the early Cretaceous (130 Ma) and culminated at 120 Ma. Almost all the Wugongshan granitic plutons were derived from the partial melting of Mesoproterozoic crustal material, with little mantle components. We also discuss the provenance of the metasedimentary rocks and pre-Mesozoic crustal evolution of Cathaysia. [ABSTRACT FROM AUTHOR]

The Damiao igneous complex is a composite gabbro-anorthosite suite that was emplaced during the post-collisional extensional stage following the amalgamation of the Eastern and Western Blocks within the North China Craton (NCC). This magmatic suite is composed of anorthosite, leuconorite, gabbroic anorthosite, norite, gabbronorite, noritic gabbro, ferrodiorite, Fe-Ti-(P) rich gabbro and Fe-Ti ore. We present zircon LA-ICP-MS U–Pb age data on noritic gabbro, norite, leuconorite, gabbronorite, and gabbroic anorthosite from the Damiao suite. The data yield weighted mean 207 Pb/ 206 Pb ages of 1725 ± 13 Ma, 1687 ± 18 Ma, 1751 ± 15 Ma and 1693 ± 24 Ma, 1721 ± 17 Ma, and 1729 ± 14 Ma respectively suggesting a relatively long-lived crystallization process within the magma chamber during late Paleoproterozoic. The different lithologies show similar rare earth element patterns indicating a co-magmatic nature and derivation from the same magma chamber through polybaric crystallization and differentiation. The high alumina dykes of gabbronorite and noritic gabbro which are chemically identical to the parental magmas of high alumina gabbros from elsewhere and exhibit an upper mantle origin with high degree melting of spinel-bearing mantle facies. Their zircon ɛ Hf ( t ) compositions plot along the evolution line of the 2.5–3.0 Ga Neo- to Mesoarchean basement rocks in the NCC (−9.2 to −3.3) and the relatively low Cr, Ni contents (Cr: 9.33–338 ppm; Ni: 8.62–182 ppm), high Th/Ta (>2.90), Ba/Zr (>20.18), and low Nb anomaly ( Nb/Nb * = Nb PM / ( Th PM × La PM ) < 0.50 ) for chemically equivalent parental rocks deviate from typical mantle-derived melts, suggesting the input of Archean crustal components. We propose that the magma was sourced from spinel-bearing sub-continental lithospheric mantle at depths of up to 60 km, within a post-collisional extensional setting, and assimilated Archean crustal components before ascent. The heat input for the extensive melting might have come from upwelling asthenosphere triggered by the break-off of the subducted oceanic slab following the collision between the Eastern and Western Blocks of the NCC. The deep seated magma was channeled to mid-crust depth along rift zone and underwent low pressure crystallization and differentiation to form the Damiao suite. [ABSTRACT FROM AUTHOR]

Sandwiched between the Dharwar Craton in the north and the Neoarchean–Proterozoic crustal blocks to the south, the Coorg Block in southern India is composed dominantly of a suite of arc magmatic rocks including charnockites, TTG (tonalite–trondhjemite–granodiorite)-related granitoid suite and felsic volcanic tuffs together with minor accreted oceanic remnants along the periphery of the block. Coeval mafic and felsic magmatism with magma mixing and mingling in an arc setting is well represented in the block. Here we present the petrology, geochemistry, zircon U–Pb geochronology and Lu–Hf isotopes of all the major lithologies from this block. Computation of metamorphic P–T conditions from mineral chemical data shows consistent granulite-facies P–T conditions of 820–870 °C and up to 6 kbar. Our geochemical data from major, trace and REE on representative samples of the dominant rock types from the Coorg Block corroborate an arc-related signature, with magma generation in a convergent margin setting. The zircon data yield weighted mean 207 Pb/ 206 Pb ages of 3153.4 ± 9 to 3184.0 ± 5.5 Ma for syenogranites, 3170.3 ± 6.8 Ma for biotite granite, 3275 ± 5.1 Ma for trondhjemite, 3133 ± 12 to 3163.8 ± 6.9 Ma for charnockites, 3156 ± 10 to 3158.3 ± 8.2 for mafic enclaves, 3161 ± 16 Ma for diorite and 3173 ± 16 Ma for felsic volcanic tuff. An upper intercept age of 3363 ± 59 Ma and a lower intercept age of 2896 ± 130 Ma on zircons from a charnockite, as well as an evaluation of the Th/U values of the zircon domains against respective 207 Pb/ 206 Pb ages suggest that the Mesoarchean magma emplacement which probably ranged from > 3.3 to 3.1 Ga was immediately followed by metamorphism at ca. 3.0 to 2.9 Ga. The ages of magmatic zircons from the charnockites and their mafic granulite enclaves, as well as those from the volcanic tuff and biotite granite, are all remarkably consistent and concordant marking ca. 3.1 Ga as the peak of subduction-related crust building in this block, within the tectonic milieu of an active convergent margin. The majority of zircons from the Coorg rocks show Hf isotope features typical of crystallization from magmas derived from juvenile sources. Their Hf crustal model ages suggest that the crust building might have also involved partial recycling of basement rocks as old as ca. 3.8 Ga. The crustal blocks in the Southern Granulite Terrane in India preserve strong imprints of major tectonothermal events at 2.5 Ga, 2.0 Ga, 0.8 Ga and 0.55 Ga associated with various subduction–accretion–collision or rifting events. However, the Coorg Block is exceptional with our data suggesting that none of the above events affected this block. Importantly, there is also no record in the Coorg Block for the 2.5 Ga pervasive regional metamorphism that affected all the other blocks in this region. The geochronological data raise the intriguing possibility that this block is an exotic entity within the dominantly Neoarchean collage in the northern domain of the Southern Granulite Terrane of India. The Mesoarchean arc-related rocks in the Coorg Block suggest that the magma factories and their tectonic architecture in the Early Earth were not markedly different from those associated with the modern-style plate tectonics. [ABSTRACT FROM AUTHOR]

The Trans-North China Orogen (TNCO) along the central part of the North China Craton (NCC) is considered as a Paleoproterozoic suture along which the Eastern and Western Blocks of the NCC were amalgamated. Here we investigate the Precambrian crustal evolution history in the Fuping segment of the TNCO and the subsequent reactivation associated with extensive craton destruction during Mesozoic. We present zircon LA-ICP-MS U–Pb and Lu–Hf data on TTG (tonalite–trondhjemite–granodiorite) gneiss, felsic orthogneiss, amphibolite and granite from the Paleoproterozoic suite which show magmatic ages in the range of 2450–1900 Ma suggesting a long-lived convergent margin. The ε Hf ( t ) values of these zircons range from −11.9 to 12 and their model ages suggest magma derivation from both juvenile components and reworked Archean crust. The Mesozoic magmatic units in the Fuping area includes granite, diorite and mafic microgranular enclaves, the zircons from which define a tight range of 120–130 Ma ages suggesting a prominent Early Cretaceous magmatic event. However, the ε Hf ( t ) values of these zircons show wide a range from −30.3 to 0.2, indicating that the magmatic activity involved extensive rejuvenation of the older continental crust. [ABSTRACT FROM AUTHOR]

The Southern Granulite Terrane (SGT) in India preserves the records of the formation and recycling of continental crust from Mesoarchean through Paleoproterozoic to Neoproterozoic and Cambrian, involving multiple subduction–accretion–collision associated with major orogenic cycles. A chain of unmetamorphosed and undeformed alkaline magmatic intrusions occurs along the northern margin of the SGT aligned along paleo-suture zones. Here we investigate two representative plutons from this suite, the Angadimogar syenite (AM) and the Peralimala alkali granite (PM) through field, petrological, geochemical, zircon U–Pb and Lu–Hf studies. Magma mixing and mingling textures and mineral assemblages typical of alkaline rocks are displayed by these plutons. The whole-rock major and trace element data characterize their alkaline nature. In trace element discrimination diagrams, the AM rocks straddle between the VAG (volcanic-arc granites) and WPG (within plate granites) fields with most of the samples confined to the VAG field, whereas the PM rocks are essentially confined to the WPG field. The diversity in some of the geochemical features between the two plutons is interpreted to be the reflection of source heterogeneities. Most zircon grains from the AM and PM plutons display oscillatory zoning typical of magmatic crystallization although some grains, particularly those from the PM pluton, show core-rim structures with dark patchy zoned cores surrounded by irregular thin rims resulting from fluid alteration. The weighted mean 206 Pb/ 238 U ages of the magmatic zircons from three samples of the AM syenite are in the range of 781.8 ± 3.8 Ma to 798 ± 3.6 Ma and those from two samples of the PM alkali granite yield ages of 797.5 ± 3.7 Ma and 799 ± 6.2 Ma. A mafic magmatic enclave from the AM pluton shows weighted mean 206 Pb/ 238 U age of 795 ± 3.3 Ma. The AM and PM plutons also carry rare xeneocrystic zircons which define upper intercept concordia ages of 3293 ± 13 Ma and 2530 ± 22 Ma correlating with the ages of the basement rocks from these areas. The initial 176 Hf/ 177 Hf isotope ratios of the zircon grains from the AM syenite fall in the range between 0.281771 and 0.282284, with moderately negative εHf(t) values between − 5.9 and 0.1. Similarly, the initial 176 Hf/ 177 Hf isotope ratios for the zircon grains of PM ultrapotassic granite range between 0.281197 and 0.281970, albeit with more negative εHf(t) values in the range between − 22.7 and − 0.3 (average εHf (t) value − 18.8). The Lu–Hf data suggest the involvement of variable extent of older crust with distinct crustal residence times, either in the form of assimilation during magma emplacement, or crustal recycling during magma genesis. Based on the geochemical and isotopic systematics, a possible petrogenetic model would be asthenospheric upwelling in an extensional setting, melting of enriched lithosphere, and interaction of the magmas with lower crustal domains with subduction-related components of various ages. The disposition of these alkali plutons along two paleo sutures that weld the Meso-Neoarchean crustal blocks in the northern periphery of SGT suggests that the zones of emplacement might represent an aborted rift. The paleo-sutures probably served as a weak zone along which extension occurred broadly coeval with the Cryogenian subduction further south. [ABSTRACT FROM AUTHOR]

Charnockites (pyroxene-bearing granitoids) of magmatic origin in diverse tectonic settings and ranging in age from Mesoarchean to Cretaceous constitute important components of the continental crust. Here we report charnockites displaying both magnesian and ferroan compositions associated with gabbros from an AMCG (anorthosite–mangerite–charnockite–granite) suite in the North China Craton. The orthopyroxene in the magnesian charnockite is characterized by moderate X Mg of 0.63–0.65 (Wo 1–2 En 62–63 Fs 35–36 ), and low Al 2 O 3 content of 0.59–0.71 wt.%. The magnesian charnockites show medium- to high-K contents, and high Mg# (~ 47–69) similar to that of gabbros, whereas the Mg# of the ferroan charnockites is low (~ 6–28). The ferroan charnockites are alkali-calcic to alkalic, and weakly peralkaline to metaluminous, whereas the magnesian charnockites are calcic to calc-alkalic, and metaluminous. Although magnesian charnockites are in general considered to have formed in subduction setting, the medium- to high-K contents, high Mg# values with a wide range, and the highly negative εHf values of the zircons in these rocks (− 8. 4 to − 13.6), suggest inheritance of the arc signature from the melting of ancient arc-related crustal material. The ferroan charnockites show tholeiitic affinity and define a common differentiation trend with the gabbroic anorthosites and likely represent fractionated end-members with or without crustal interaction in a post-collisional rift setting. We present U–Pb age data from zircon grains on seven samples including two ferroan charnockites, three magnesian charnockites, one gabbroic enclave in magnesian charnockite and one gabbroic anorthosite which show emplacement ages of 1748.8 ± 6.4 Ma, 1747.1 ± 9.5 Ma, 1756.4 ± 7.3 Ma, 1756.7 ± 9.2 Ma, 1731 ± 17 Ma, 1731.6 ± 8.2 Ma and 1746.5 ± 7.3 Ma respectively. The negative εHf values (− 1.2 to − 13.6) of zircon grains from these rocks and the older crustal model ages ranging from Mesoarchean to Paleoproterozoic suggest that the magma sources of these rocks involved the melting of ancient crustal components. The age data suggest that the magmatic suite was emplaced within a relatively short time interval between1.73 and 1.76 Ga, during late Paleoproterozoic, placing the rocks suite in a post-collisional scenario, following the amalgamation between the Eastern and Western Blocks of the North China Craton along the Trans-North China Orogen at ca. 1.85–1.80 Ga. [ABSTRACT FROM AUTHOR]

The Attappadi area on the south-western flanks of the Archean Dharwar Craton in southern India is located along the E–W trending Bhavani Shear Zone which marks the trace of a Neoarchean suture zone. The dominant rock types in the area include meta-ultramafics, amphibolites, TTG (tonalite–trondhjemite–granodiorite) gneisses, metapelites, and sulphidic banded iron formation (BIF). Here we report the occurrence of felsic volcanic rocks preserving primary textures from the Anaikatti area in eastern Attappadi. The felsic volcanics are interbanded with the BIF, amphibolite, metapelite, metapyroxenite and hornblende gneisses. The felsic volcanics are divided into two types based on their textures. The Type-1 rock is medium grained with gneissic texture and lack unequivocal primary volcanic textures. Type-2 felsic volcanics are thinly laminated, fine grained and at places preserve relict soft-sediment deformation structures. They also contain relict volcanic clasts or lapilli and are interpreted as felsic tuff. Geochemically, the Attappadi felsic volcanics are rhyolitic in composition and have arc-related trace element signatures. They also possess a calc-alkaline volcanic affinity. We report LA-ICPMS U–Pb ages from zircons in four samples of the felsic tuffs which show weighted mean ages of 2567 ± 18 Ma and (MSWD = 1.4), 2499 ± 19 Ma (MSWD = 0.57), 2555 ± 24 Ma (MSWD = 1.7) and 2576 ± 64 Ma (MSWD = 5.8). The late Neoarchean–early Paleoproterozoic ages obtained in our study correlate well with the zircon U–Pb ages reported in recent studies from ophiolites and other suprasubduction suites from Attappadi and surrounding regions. The zircon ε Hf values range from − 11.1 to 7.6 suggesting heterogeneous source material involving both juvenile and older reworked components. We build a tectonic model for the SW margin of the Dharwar Craton with an oceanic realm characterized by island arcs and widespread submarine tholeiitic as well as komatiitic ultramafic and mafic volcanism during the Neoarchean. This predominantly mafic volcanism on the ocean floor is represented by primitive komatiitic lavas, oxide and sulphide facies BIF. The birth of volcanic arc at the convergent margin is marked by felsic volcanism and the deposition of felsic volcanics and volcano-sedimentary successions. In the final stage of ocean closure, the ocean-plate and continental arc assemblages were brought in juxtaposition including the accretion of the ophiolitic fragments. Our study confirms the recent models of arc–arc and arc–continental accretion to the southern margin of the Dharwar Craton and major continental growth at the end of the Archean. [ABSTRACT FROM AUTHOR]

Highlights: [•] Nilgiri Block dominantly composed of charnockite-mafic granulite-amphibolite-ultramafic suite. [•] Geochemical features reveal arc magmatism in a convergent margin. [•] Zircon U–Pb ages reveal Neoarchean magmatism closely followed by metamorphism. [•] Correlation with Neoarchean crustal growth in the Early Earth. [ABSTRACT FROM AUTHOR]

Highlights: [•] Zircon U–Pb data from granitoids of Indochina Block which show ages ranging from 754 to 767Ma. [•] The Hf isotopic data and geochemical signatures suggest calc-alkaline magmas generated in a subduction-related setting. [•] We propose the juxtaposition of India and Indochina in the Gondwana reconstruction. [ABSTRACT FROM AUTHOR]