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Petrological and major-trace element mineral chemistry studies have been carried out on pyroxenites from the Pakkanadu alkaline-ultramafic complex from the southern India to understand their origin and nature of magma responsible for ultramafic magmatism in the area. Pyroxenites display cumulus texture and consist of clinopyroxenes (cpx) and amphiboles (amp) as dominant phases with a subordinate amount of apatite, biotite, ilmenite, magnetite, pyrite, sphene, and calcite. Mineral chemistry classifies cpx as augite and diopside, whereas amp falls under tremolite-actinolite and hornblende- actinolite fields. Cpx are alkaline to sub-alkaline in composition and Mg# -- Al2O3 compositions suggest their crystallization under high-pressure conditions. A negative correlation between Mg# and TiO2 in cpx suggests early crystallization of magnetite and pyrite; high Mg# (76-92) suggests its link with the Alaskan- type intrusions, which may be crystallized through fractionation-accumulation Processes. Tectonic discrimination diagrams for cpx argue for the magmatic emplacements underan arc-tholeiitic environment in a subduction zone setting. Amp mineral chemistry (high SiO2 and low TiO2) indicate as the products of hydrothermal alteration of clinopyroxenes. A Low Al/Si ratio in the cpx suggests their derivation from silica-oversaturated magma, whereas low-Ti contents reflect slow cooling rate of the magma. Positive Rb, Ba and U anomalies in the multi-element patterns of the cpx probably signifying varying degrees of hydrothermal alteration in the studied samples. However, consistent Nb-Ta depletion can also be attributed to an enriched mantle source of the magma from which pyroxenites were crystallized. Moreover, single-cpx geothermobarometry yielded a crystallization temperature of 905 to 911°C under moderate to high pressure of 3-9 kbar. [ABSTRACT FROM AUTHOR]

Field studies around Pulivendla (14°33′36″N: 78°19′48″E) belonging to the Tadpatri Formation of Proterozoic Cuddapah Basin document three distinct lava flows (based on internal layering), associated sediments (shale and sandstone) and intrusive dyke-sill system. The presence of previously undocumented internal layering namely Lower Vesicular Zone (LVZ), Lower Colonnade Zone (LCZ), Entablature Zone (EZ), Upper Colonnade Zone (UCZ) and Upper Vesicular Zone (UVZ) helps to delineate three lava flows in the study area. The associated sedimentary beds either correspond to lava cessation-period or dynamic lava-sediment interaction due to lava-cascading. The present study in Tadpatri Formation reveals volcano-sedimentological features analogous to that of Deccan Traps. It is postulated that magmatism within Tadpatri Formation might have been largely controlled by Proterozoic syn-rift plume activity (needs further corroboration by high precision major/trace/isotopic analyses). [ABSTRACT FROM AUTHOR]

The Assam-Meghalaya Gneissic Complex (AMGC) of northeast India contains numerous Pan-African granitic bodies that have been attributed to post-collisional rift-related magmatism. The present study is concerned with the first appraisal of intermediate magmatism (diorite, monzonite, and monzodiorite) found in the Borjuri Pluton of Mikir Massif, which is the eastern extension of AMGC. The diorites are strongly metaluminous and exhibit enriched LREE ([La/Yb]N = 1.63–7.37) with respect to HREE ([Gd/Yb]N = 1.95–2.27). The studied rocks do not show any mineralogical or textural indication of metamorphism. Tectonic discrimination diagrams indicate that these rocks originated in a within-plate tectonic setting. The lower Mg# (33.49–38.69), low Cr (below detection limit), and Ni (27–41 ppm) contents along with elemental ratios such as Rb/Sr (0.32–0.95), La/Nb (0.49–4.21), and Nb/Ce (0.11–0.64) suggest a crustal source for the diorites. Discrimination diagrams coupled with elemental ratios suggest that these rocks originated due to partial melting of mafic components in the crust with possible contribution from mantle materials. The P–T conditions of diorite emplacement (7.4 kbar, 688 °C) were calculated using the amphibole-plagioclase geothermobarometer. Geochemical and geochronological data of the Pan-African felsic plutons reported from the AMGC indicate that these rocks were emplaced in a post-collisional extensional regime. The Borjuri Pluton is in close proximity with the Kathalguri Pluton, which has been reported as a product of Pan-African magmatism. In view of the numerous extensional Pan-African felsic magmatism reported from the AMGC and based on the close vicinity of the Borjuri diorites with the Kathalguri granites, we speculate that the Borjuri diorites are products of the Pan-African post-collisional magmatism. [ABSTRACT FROM AUTHOR]

The titanium (Ti) concentrations in zircon and quartz and corresponding thermometers have been regarded as powerful monitors that constrain petrogenetically meaningful temperature conditions of crystallization and metamorphism. The precise measurement of trace elements by electron probe microanalyzer (EPMA) is quite challenging as their x‐ray intensities are only slightly higher than the Bremsstrahlung background, leading to significant errors while quantifying the elemental abundances (e.g., Ti‐in‐zircon). We present EPMA‐based protocols for analysing Ti concentrations in zircon and quartz by considering recent analytical and instrumental improvements. High counting times at peak and background positions, simultaneous acquisition of Ti in multiple (three) spectrometers and data processing using the non‐central chi2 test for risk determination in sub‐counting method were employed in Ti‐in‐zircon and Ti‐in‐quartz protocols. Applying these protocols to the Mongolian garnet, San Carlos olivine and NIST 610 glass standards yielded Ti concentrations of 0.60 ± 0.02 wt%, 18 ± 3 ppm and 437 ± 26 ppm (in ±2σ), respectively. The Ti concentrations obtained from these standards are consistent with those published based on high‐precision analytical methods. We use the existing Ti‐in‐zircon and Ti‐in‐quartz thermometers to understand the thermal evolution of various lithologies in the Sandmata Complex, Aravalli Craton (north‐western India). The investigated samples include garnet–biotite gneiss, migmatite gneiss, mafic granulite and Anjana granite. The Ti‐in‐zircon temperatures calculated from the patchy‐zoned zircon cores yield HT–UHT conditions (892–959°C) for garnetiferous granite gneiss, migmatite gneiss and mafic granulite, whereas the zircon overgrowths yield temperatures of 725–871°C. The homogeneous zircon cores from Anjana granite yield temperatures (914–984°C) comparable to zirconium saturation conditions (920–960°C), indicating zircon crystallization from "hot" granitic melt. The oscillatory overgrowths on the zircon core obtain variable temperature conditions for inner overgrowth (811–877°C) and outer overgrowth (714–782°C), suggesting the episodic growth of zircon grains from different magma pulses. Additionally, the application of pressure‐dependent Ti‐in‐quartz thermometry yields quartz recrystallization conditions for garnet–biotite gneiss (430–556°C), migmatite gneiss (423–593°C), mafic granulite (430–679°C) and Anjana Granite (444–533°C). The combination of Ti‐in‐zircon thermometry, Ti‐in‐quartz and conventional thermobarometry demonstrates cooling histories for various high‐grade metamorphic and magmatic rocks in the Sandmata Complex. Based on this study, we emphasize that trace element thermometers can decipher high‐temperature metamorphism, which is otherwise erased in conventional thermometers due to diffusional readjustments during long‐lasting near‐peak and post‐peak metamorphism. [ABSTRACT FROM AUTHOR]

Most of Earth's volcanism occurs at tectonic plate boundaries associated with subduction or rifting processes. The mantle plume hypothesis is an important supplement to plate tectonics for explaining some high-volume intraplate volcanic fields. However, many intraplate magmatic provinces occur as low-volume, monogenetic basalticsuite fields that are neither associated with plate-boundary processes nor attributable to mantle plumes, and the origin of such magmatism has long been debated. Identification of their source characteristics and possible mechanisms that trigger mantle melting will provide essential insights into Earth's mantle heterogeneity and also develop our knowledge of tectonic plate movement through time. Here, we report new geochronology, mineral chemistry (especially olivine), and whole-rock chemical and Sr-Nd-Pb-Hf isotopic compositions on Cenozoic intracontinental alkaline basalts from the northwestern Tarim craton (central Asia), aiming to better assess the origin of Earth's low-volume effusive intraplate volcanic fields. The basalts (ca. 42 Ma) have olivine (e.g., mean Ni abundances of ~2250 ppm, mean Mn/Zn ratios of 13.7) and whole-rock chemistry consistent with their derivation from a mixed peridotite-pyroxenite source. Moderately depleted Sr-Nd-Pb-Hf isotopes (87Sr/86Sr = 0.7039-0.7053; εNd = +4.0 to +5.5; 206Pb/204Pb = 18.247-18.535; εHf = +8.1 to +8.7) require a young (ca. 500 Ma) oceanic crust recycled into the source, possibly related to subduction events during the assembly of Pangea. Estimated thermal-chemical conditions indicate that the original melting occurred in a relatively dry (H2O = 1.4 ± 0.9 wt%) and reduced (logfO2 ΔFMQ = -0.97 ± 0.21, where FMQ is fayalite-magnetite-quartz) asthenosphere under a mantle potential temperature of ~1420 °C and a pressure of ~3.7 GPa (corresponding to a depth of ~120 km). Combining these data with regional tectonic history and geophysical data (high-resolution P-wave tomography), we propose that the longlasting India-Eurasia collision triggered asthenospheric upwelling, focusing melts along translithospheric zones of weakness; this model provides a robust explanation for the observed Cenozoic intracontinental volcanism in central Asia. The integrated geochemical and geophysical evidence reveals that plate subduction--induced mantle upwelling represents a likely mechanism for the generation of many regions of plume-absent intraplate magmatism within continents. [ABSTRACT FROM AUTHOR]

The continental crust in the overriding plate of the India-Asia collision zone in southern Tibet is characterized by an overthickened layer of felsic composition with an underlying granulite-eclogite layer. A large data set indicates that this crust experienced magmatism from 245 to 10 Ma, as recorded by the Gangdese Batholith. Magmatism was punctuated by flare-ups at 185−170, 90−75, and 55−45 Ma caused by a combination of external and internal factors. The growth of this crust starts with a period dominated by fractional crystallization and the formation of voluminous (ultra)mafic arc cumulates in the lower crust during subduction, followed by their melting during late-subduction and collision, due to changes in convergence rate. This combined accumulation-melting process resulted in the vertical stratification and density sorting of the Gangdese crust. Comparisons with other similarly thickened collision zones suggests that this is a general process that leads to the stabilization of continental crust. The Gangdese Batholith records the time-integrated development of the world's thickest crust, reaching greater than 50 km at 55–45 Ma and greater than 70 km after 32 Ma. The Gangdese Batholith records three magmatic flare-ups in response to distinct drivers; the last one at 55−45 Ma marks the arrival of India. Magmatism was first dominated by fractional crystallization (accumulation) followed by crustal melting: the accumulation-melting process. Accumulation-melting in other collision zones provides a general process for vertical stratification and stabilization of continental crust. [ABSTRACT FROM AUTHOR]

The Shyok Suture Zone is an oceanic remnant of the Neo-Tethyan ocean sandwiched between the Ladakh Batholiths to the south and Karakoram Batholith to the north. The Tirit granitoids in this suture are dark-coloured, relatively rich in ferromagnesian minerals and range from granodiorite–tonalite to gabbro–diorite in composition. Mafic igneous enclaves are quite common and they are intruded by NW–SE parallel doleritic and aplitic dykes. The Tirit granitoids have a wide range of major oxide compositions (SiO2 = 52.1–72.11 wt %, TiO2 = 0.21–1.23 wt %, Al2O3 = 11.42–13.52 wt %, MgO = 1.69–10.69 wt % and CaO = 3.24–9.31 wt %) and show calc-alkaline, metaluminous, I-type characteristics, transitional between primitive and mature arc continental plutons. Rare earth elements (REE) show considerable enrichment in light REE (LREE) as compared to the heavy REE (HREE). Late Cretaceous U/Pb dates (74–68 Ma) show that they formed during the pre-collision northward movement of India. The Tirit dykes are only slightly younger and probably part of the same episode. [ABSTRACT FROM AUTHOR]

How the Neotethyan Ocean evolved and extended southwards into Southeast Asia remains controversial. The paleographical correlation between India and the SE Asian blocks and/or terranes before the opening of the Neotethys and the initial opening time of the Neotethys is still unknown. The lack of this knowledge hampers our further understanding of the tectonic evolution of global Neotethys. Here we present a combined study on Triassic magmatism in the Tengchong Block and Triassic sedimentation in the Myitkyina area, located on the two sides of the Tagaung-Myitkyina Ophiolite Belt of northern Myanmar. Our results coupled with previous data demonstrate that a Triassic continental magmatic arc developed in the Tengchong Block and that the Triassic Myitkyina sedimentary sequence was part of the Tethyan Himalayan Langjiexue Group in northern India. Moreover, the Tengchong Triassic magmatic arc provided important detrital inputs to the whole Langjiexue Group of northern India. Such a provenance is the best explanation for the Permian--Triassic detrital zircons of the Langjuexue Group. Together, we propose that the Tagaung-Myitkyina Ophiolites in northern Myanmar are the relics of the Neotethyan Ocean rather than the Mesotethyan Ocean (Bangong-Nujiang Ocean) in SE Asia, and that the initial opening time of the Neotethys was the Early Jurassic of 200-190 Ma. Then, the earliest (185-165 Ma) intra-oceanic arc akin to the Izu-Bonin-Mariana arc in the West Pacific, developed soon after the Late Triassic opening of the Neotethys. [ABSTRACT FROM AUTHOR]

The type of lithosphere subducted between India and Tibet since the Paleocene remains controversial; it has been suggested to be either entirely continental, oceanic, or a mixture of the two. As the subduction history of this lost lithosphere strongly shaped Tibetan intraplate tectonism, we attempt to further constrain its nature and density structure with numerical models that aim to reproduce the observed history of magmatism and crustal thickening in addition to present-day plateau properties between 83°E and 88°E. By matching time-evolving geological patterns, here we show that Tibetan tectonism away from the Himalayan syntaxis is consistent with the initial indentation of a craton-like terrane at 55 ± 5 Ma, followed by a buoyant tectonic plate with a thin crust, e.g., a broad continental margin (Himalandia). This new geodynamic scenario can explain the seemingly contradictory observations that had led to competing hypotheses like the subduction of Greater India versus largely oceanic subduction prior to Indian indentation. By evaluating model predictions with multiple geological data, the study shows that Tibetan tectonism is most consistent with the initial indentation of a cratonic terrane, followed by subduction of a buoyant tectonic plate resembling a continental margin. [ABSTRACT FROM AUTHOR]

South China, India, and their derivative blocks preserve many similar magmatic and sedimentary records related to the tectonic transition from Rodinia to Gondwana. They provide crucial insights into not only the paleogeographic correlation between them but also the geodynamic mechanism for such a transition. Our new results, combined with published data from these blocks, reveal that South China remained linked with India at least from ca. 830 Ma to ca. 510 Ma and formed the South China-India Duo, which is located at the western margin of Rodinia. The identical magmatism and sedimentation reflect that double late Neoproterozoic rift systems in the South China-India Duo developed owing to the rollback of subducting oceanic slab beneath them. For example, an intracontinental rift developed along the Jiangnan-Aravalli-Delhi fold belt, which separated the Yangtze-Marwar block from the Cathaysia-Bundelkhand block. Another intra-arc rift developed contemporaneously along the northern and western margins of the Yangtze block, through the Marwar terrane of western India, and then into the Seychelles and Madagascar terranes. Such an intra-arc rift is the most feasible explanation for the common development of coeval arclike and extension-related magmatic rocks and extensional sedimentary sequences on the western margin of the South China-India Duo, in Seychelles and Madagascar, and even at other subduction zones. South China was finally separated from Indian Gondwana at ca. 510 Ma due to the opening of the Proto-Tethys Ocean. [ABSTRACT FROM AUTHOR]

The origin and formation of the continental collision-related magmas remain elusive. The volcanic rocks erupted during India-Asia continental collision offer an ideal opportunity to explore their genesis and geodynamic process. Here, we report new zircon U-Pb dating results and Hf isotope, whole-rock element and Sr-Nd isotope data of volcanic rocks in Linzhou Basin, central Lhasa Terrane, southern Tibet. These volcanic rocks are mainly comprised of andesites and belong to Dianzhong Formation. The timing of their formation is ca. 63–66 Ma, coeval with the India-Asia continental initial collision in the central part of southern Tibet. All these rocks show an arc-like geochemical affinity and they have more depleted Sr-Nd-Hf isotopic compositions (87Sr/86Sri = 0.705006–0.705963, εNd(t) = −1.78 to 3.52, zircon εHf(t) = 1.2–7.0) than the Cretaceous pre-collisional andesites and Eocene ancient lithospheric mantle-derived melts beneath the central Lhasa Terrane. The correlation between Mg# and CaO, TiO2, Al2O3, Sr/Y, 87Sr/86Sr, εNd(t) suggests that they were likely hybrid production between an isotopically depleted end-member and the enriched lithospheric mantle (ELM). The oceanic crust-derived melts would be the best candidate for the former end-member according to their depleted Sr-Nd isotopic compositions. The andesitic rocks of Dianzhong Formation in the central Lhasa Terrane were most likely stemmed from partial melts of altered Neo-Tethyan crust and then mixed with the ELM-derived melts. Given the Cretaceous-Tertiary upper crustal shortening, back-arc extension, and voluminous volcanism in the Lhasa Terrane, along with abrupt increasing in the magma temperature and the convergence rate between India and Asia during Palaeocene, the occurrence of the Dianzhong Formation volcanic rocks can be well explained by the Neo-Tethyan slab roll-back. The mixing between the oceanic crust- and the continental lithospheric mantle-derived melts induced by the oceanic slab roll-back would be a complimentary scenario for the formation of the syn-collisional magmatism in collisional orogeny belts. [ABSTRACT FROM AUTHOR]

The immense Tibetan Plateau is a masterpiece of the ongoing India–Asia collision. The timing of the collision is a critical parameter to reconstruct the plateau evolution, but has been not well understood yet. Here, we report a newly discovered Eocene (53.8 Ma) shoshonitic intrusion with the input of Indian continental material in the Yangbajing area of the Lhasa Terrane, south Tibet. The reverse 207Pb/206Pb zoning exhibited by feldspars, the linear isotopic arrays between whole‐rock 187Os/188Os and 1/188Os, the in‐situ feldspar 208Pb/204Pb and 206Pb/204Pb values, and the in‐situ zircon εHf(t) values and δ18O values strongly demonstrate a binary interaction process for the generation of the Yangbajing shoshonitic intrusion. Our Os isotopes further illustrate that the interaction process was dominated by recycled crustal melt assimilating minor mantle melt. In addition, different isotopic systems consistently point to an end‐member represented by the underthrust crust slice of Indian continent, which indicates that the Indian lithosphere must have already subducted beneath the Lhasa Terrane at 53.8 Ma. This is also supported by the abrupt isotopic shift toward the enriched values and the composition variation toward the high potassium contents in the subsequent Tibetan magmatism, corresponding to an increasing involvement of the Indian continental crust into the upper plate magmatism. Therefore, the Yangbajing shoshonitic intrusion is one of the earliest known magmatic evidence for the onset of the India–Asia collision. Plain Language Summary: The timing of the ongoing India–Asia collision is a critical parameter to reconstruct the plateau evolution. Here, we report a newly discovered Eocene shoshonitic intrusion with the input of Indian continental material in the Yangbajing area of the Lhasa Terrane, south Tibet. The reverse 207Pb/206Pb zoning exhibited by feldspars, the linear isotopic arrays between whole‐rock 187Os/188Os and 1/188Os, the in‐situ feldspar 208Pb/204Pb and 206Pb/204Pb values, and the in‐situ zircon εHf(t) values and δ18O values strongly demonstrate a binary interaction process for the generation of the Yangbajing shoshonitic intrusion. Our Os isotopes further illustrate that the interaction process was dominated by recycled crustal melt assimilating minor mantle melt. In addition, different isotopic systems consistently point to an end‐member represented by the underthrust crust slice of Indian continent, which indicates that the Indian lithosphere must have already subducted beneath the Lhasa Terrane at 53.8 Ma. Key Points: The early Eocene Yangbajing intrusion in the Lhasa Terrane was generated at 53.8 MaThe intrusion has recorded the subducted front of Indian Plate beneath Tibetan Plateau in the early EoceneThe onset of the India–Asia collision was prior to 53.8 Ma [ABSTRACT FROM AUTHOR]

Wehrlite xenoliths recovered from lamprophyre dykes from Sarnu–Dandali alkaline igneous complex record three distinct events of modification in the mantle below northwest India. The first event marks mantle metasomatism by carbonate-rich fluids from the upwelling mantle, which formed secondary olivine and clinopyroxene at the expense of orthopyroxene, in mantle peridotite with little or no orthopyroxene. The phlogopite veining characterizes the second event in the mantle during rifting. These veins are formed by the crystallization of upwelling silica undersaturated alkaline fluids along the fractures and grain boundaries in the carbonated metasomatized mantle. Petrographic observations reveal separate phlogopite veins and carbonate infiltrations where carbonate activity preceded the phlogopite veining. The final event is an eruption of lamprophyres and mela-nephelinites in the study area at the later phase of the Deccan eruption, transporting wehrlite xenoliths to the surface. Estimated temperatures range from 911° to 940°C and pressure from 15.6 to 19.3 kbar with an average of 18.5 kbar, showing their derivation from a shallower depth of subcontinental lithospheric mantle (56–67 km). Separation of Greater-Seychelles from India at c. 68.5 Ma under extensional tectonic settings led to the lithosphere thinning and formation of wehrlite xenoliths in the rift margins. [ABSTRACT FROM AUTHOR]

Present study of vanadium mineralization in the Sonia sandstone of Jodhpur Group shows first hydrothermal activity in the Sonia sandstone of Marwar Supergroup. The Sonia sandstone served as a host for the mineralizing solutions. The vanadium mineralization occurred in sandstone- gritty sandstone-conglomerate along faults. Field relationship and petrological study suggests that mineralization is filled by epithermal solutions and provide a better understanding of the timing and nature of the alteration processes. Though the source of the vanadium is not well constrained, but is possibly from the partial melting of banded gneissic complex-II (Sirohi Group), the source (crustal) melt had assimilated material from the rocks of Sirohi Group in significant amount. Deposition of tuffs at top of Sonia Formation (Chhoti Khatu) and emplacement of last stage Malani dykes suggest that the last phase of Malani magmatism generated heat for the partial melting of banded gneissic complex-II (Sirohi Group). The occurrence of vanadium in sandstone—gritty sandstone—conglomerate from Sonia Formation of Marwar Supergroup has opened a new chapter to explore uranium which generally occurs after vanadium mineralization in conglomeratic sedimentation. [ABSTRACT FROM AUTHOR]

The present study reports fayalite-bearing granite bodies from the Assam-Meghalaya Gneissic Complex of North East India. These are weakly peraluminous with high amounts of alkalis and meagre contents of magnesium, calcium, titanium and phosphorus. The chondrite normalized REE pattern is flat, having minor enrichment of HREE with negative europium anomaly suggesting their A-type character. The discrimination based on Rb, Y, Yb, Nb and Sc content indicates their generation due to melting of crustal components. Early crystallized fayalite and fluorite grains indicate that their emplacement in an extensional tectonic set-up most possibly represents the final stage of Rodinia Supercontinent amalgamation. [ABSTRACT FROM AUTHOR]

Mafic extrusive rocks (basalts) and intrusive rocks (gabbros) from the Nagaland–Manipur Ophiolite (NMO) of the Indo–Myanmar Orogenic Belt (IMOB), north‐east India, are investigated to understand their magmatic evolution in diverse tectonic environments. Basalts are distinguished into two types: basalt‐I and basalt‐II. Basalt‐I type shows the sub‐alkaline character with Nb/Y < 0.50, low Nb/Th (2.36–7.94), and low to moderate La/Sm (1.00–4.12) indicating derivation from a slightly enriched mantle source and also supported by their enriched LREE pattern with flat HREE. They are depleted in HFSEs (Nb and Ti) but enriched in U and Pb, which is indicative of a typical subduction origin derived from an MORB‐type mantle source. Investigated samples of basalt‐II and gabbros have an equal composition with alkaline characteristics. They have Nb/Y > 0.50, high Nb/Th (8.38–13.37), and highly enriched LREE (La/Sm = 4.41–6.35) pattern. They show typical Ocean Island Basalt (OIB) characters of a plume source. The two sets of basalts and gabbros found in this study have no sign of genetic relationship, and therefore, it strongly suggests that they were derived from two different mantle sources of a plume and a subduction zone mantle wedge. Our study supports the theory that the NMO has records of different magmatic episodes produced ranging from plume‐related magmatism, to divergent and convergent plate magmatism that were generated at diverse tectonic settings. [ABSTRACT FROM AUTHOR]

The Lohit Plutonic Complex (LPC) represents Trans‐Himalayan magmatic rocks in the easternmost sector of the Himalayan Orogen. It is divided into leucogranite‐granodiorite‐diorite dominant suite in the NE and the gabbro‐diorite‐granodiorite‐granite–trondhjemite suite in the SE by the Walong Thrust. U–Pb geochronological analyses of euhedral zircon grains from different magmatic phases of LPC reveal episodic magmatism. Zircon U–Pb age of 153.4 ± 1.4 Ma of a garnetiferous granite gneiss suggest that the crustal sourced magmatism was active in Arunachal Trans‐Himalaya during the late Jurassic. U–Pb ages of subduction induced magmatic rocks of LPC range between 117 ± 0.6 Ma and 49.5 ± 0.3 Ma. A significant contribution in crustal recycling during the Oligocene–Miocene is evident from crustally derived leucogranites having U–Pb ages ranging from 35.6 ± 0.3 Ma to 30 ± 0.3 Ma. A comparison of the crystallization ages of the Western Trans‐Himalayan units with those of eastern Trans‐Himalayan units reveals an earlier onset of Tethyan arc magmatism in the eastern sector. The most prominent phase in the eastern sector is during the Late Cretaceous while western and central sector show major activity during the Palaeocene–Eocene. [ABSTRACT FROM AUTHOR]

Northwestern India was affected by the Neoproterozoic Malani and Erinpura magmatism, Cretaceous rifting, and magmatism associated with the Deccan precursors. Receiver function analysis was done using 1704 RFs from 18 stations to image and decipher the imprints of the magmatic events and comprehend the crustal modifications in terms of variations in structure and composition. The H-κ grid search and neighbourhood inversion techniques are used to retrieve the crustal structure and Vp/Vs ratios (κ). The study reveals significant variations in the crustal thickness (H = 34 km to 43 km), composition (κ =1.74 to 1.92) and shear wave velocity structure across northwestern India. The terrains encompassing the Erinpura granite and the Malani igneous suite in the vicinity of the Barmer rift are characterized by a thick (H ≥ 41 km) crust with felsic to intermediate composition (κ ≤ 1.81). The crust beneath the southern part of the Marwar basin is ≈ 38–40 km thick with mafic composition (κ > 1.81). The region around the Barmer rift has a thin crust (H = 34–36 km) with intermediate to mafic composition. The region hosting the Early Cretaceous to Paleogene alkaline complexes exhibits a high Vp/Vs ratio (κ = 1.91) that may be associated with mafic cumulates emplaced by magmatic events that overprint the signatures of the Malani event. The crust is heterogeneous with low/high velocity intracrustal layers that reflect the fractionation of magma at different depths. The mafic residue, together with magmatic intrusions, results in a mafic lowermost crust with high shear velocities of 3.9–4.0 km/s beneath most stations. Overall, northwestern India is characterized by a thick crust with intermediate crustal composition and intracrustal layering resulting from large scale magmatic events linked to the Neoproterozoic reorganization of plates and younger magmatic events. [Display omitted] • Large variations in crustal thickness and Poisson's ratio across northwestern India. • Neoproterozoic magmatism results in a thick crust with intermediate composition. • Evidence of low and high velocity intracrustal layers • Evidence of crustal thinning and emplacement of mafic cumulates by Deccan precursors. [ABSTRACT FROM AUTHOR]

Gold exploration in the Mahakoshal belt has been carried out for the past thirty years and mostly quartz veins were identified as the host targets. The recent study based on the concept of mineral system has indicated that gold occurs in mafic and ultramafic rocks also, besides the quartz veins. The mineralisation in Agori Formation is generally confined to Algoma type BIF, metavolcanics and phyllites, while in Parsoi Formation it occurs predominantly in quartz veins. The metavolcanics have acted as source rocks and the crustal deep faults have acted as conduits for mineralizing fluids, in the continental back arc type tectonic setting with two mineral systems viz. (i) basin related fluid flow with active magmatism, and (ii) magmatic related hydrothermal system. [ABSTRACT FROM AUTHOR]

The Lhasa Terrane in southern Tibet is the leading edge of the Tibet-Himalaya Orogen and represents a fragmentary record of terminal oceanic subduction. Thus, it is an ideal region for studying magmatism and geodynamic processes that occurred during the transition from oceanic subduction to continental collision and/or oceanic slab breakoff. Here we examine a suite of early Cenozoic mafic rocks (ca. 57 Ma) within the central part of Lhasa Terrane, southern Tibet, which erupted during a transitional phase between the onset of India-Asia continental collision and Neo-Tethyan slab breakoff. These rocks display a geochemical affinity with magmas produced by fluid-fluxed melting of the mantle wedge within a subduction zone environment. The whole-rock element and Sr-Nd isotope compositions of these mafic rocks are similar to those of Cretaceous subduction-related magmatism in southern Tibet, demonstrating the sustained influence of the Neo-Tethys Ocean slab on the mantle wedge during the onset of the collision of India and Asia. The results of our geochemical forward modeling constrain the conditions of melt generation at depths of 1.3-1.5 GPa with significant fluid additions from the Neo-Tethyan slab. These results provide the first petrological and geochemical evidence that slab flux-related magmatism continued despite the commencement of continental collision. While existing studies have suggested that magmas were derived from melting of the Neo-Tethyan slab during this period, our new results suggest that additional magma generation mechanisms were active during this transitional phase. [ABSTRACT FROM AUTHOR]

Deep Earth degassing is a critical forcing factor for atmospheric CO2 variations and palaeoclimate changes in Earth's history. For the Cenozoic, the key driving mechanism of atmospheric CO2 variations remains controversial. Here we analyse three stages of collision-related magmatism in Tibet, which correspond temporally with the three major stages of atmospheric CO2 variations in the Cenozoic and explore the possibility of a causal link between these phenomena. To this end we present geochemical data for the three stages of magmatic rocks in Tibet, which we use to inform a model calculating the continental collision-induced CO2 emission flux associated with the evolving Neo-Tethyan to continental subduction over the Cenozoic. The correlation between our modelled CO2 emission rates and the global atmospheric CO2 curve is consistent with the hypothesis that the India-Asia collision was the primary driver of changes in atmospheric CO2 over the Cenozoic. "Earth degassing is a critical carbon source, but its contribution to Cenozoic atmospheric CO2 variations is not well known. Here, the authors analyse CO2 fluxes on the Tibetan Plateau and suggest that the India-Asia collision was the primary driver of changes in atmospheric CO2 over the past 65 Ma." [ABSTRACT FROM AUTHOR]

U-Pb SHRIMP and LA-MC-ICP-MS zircon dates from Dalhousie and Dhauladhar granite yield weighted mean ages of 900 to 700 Ma for magmatic cores. The rim has an age of 460 Ma age, representing the time of reworking of early Neoproterozoic bodies during Cambro-Ordovician time. The plutons are composed of granite, monzogranite, and granodioritic having a peraluminous character with pronounced Eu anomaly. Higher Rb content and Rb/Sr ratio along with REE enrichment in Dalhousie granite show that the body is more evolved than Dhauladhar granite. New U-Pb data from Dalhousie and Dhauladhar areas suggest that Cambro-Ordovician continental magmatism took place within the Greater India by reworking of already existing Neoproterozoic granite. These two magmatic episodes can be correlated with the amalgamation of Gondwanaland over granite that formed during the Rodinia break-up. [ABSTRACT FROM AUTHOR]

The Banded Gneissic Complex of the Aravalli Craton of northwestern India comprises Palaeo‐ to Neoarchaean (3.3–2.7 Ga) gneisses, including tonalite–trondhjemite–granodiorite (TTG) gneisses, intruded by Neoarchaean (2.6–2.5 Ga) TTGs, sanukitoids, and potassic granites. The latter include the Malola granite that crops out near Bhilwara and forms the basement for the Mesoproterozoic Pur‐Banera mineralized belt. The granite has experienced three deformation events, represented by an S1 foliation and superimposed open folds and dextral shears. Textural evidence and thermobarometry indicate that prograde metamorphism initially forming actinolite and subsequently diopside, and culminating in the upper amphibolite facies, was followed by retrograde metamorphism in the greenschist facies with fluid influx, forming zoisite. Zircon geochronology yields a crystallization age of 2,538 ± 11 Ma and indicates a prominent metamorphic overprint in the region at 1,307 ± 9 Ma. The Malola granite has low Sr–Nd isotopic ratios, enrichments in fluid‐mobile elements (Cs, Rb, Ba, Th, and Pb), and depletions in alteration‐resistant elements (Nb, Ta, and Ti). These characteristics combined with mineralogical evidence suggest that the granite was derived by anatexis of older crystalline crust (possibly granulitic lower crust) in the same subduction zone setting inferred previously for other Neoarchean granitoids in this region. Geochemical and Sr–Nd–Hf isotopic similarities between the Malola granite and Neoarchaean granitoids of the Aravalli, Bundelkhand, Bastar, Dharwar, and Congo cratons indicate a major role for anatectic crustal reworking in their genesis. [ABSTRACT FROM AUTHOR]

The granites and granite gneisses from a tectono-metamorphic complex exposed along the Shyok Valley in the Karakoram region, India, forms the southern margin of Asian plate in the India-Asia collision zone. These rocks have been subjected to mineralogical, geochemical, and U-Pb zircon geochronological investigations to constrain the petrogenetic and geodynamic evolution of the Karakoram terrane. Outcrop-scale observations reveal the presence of pre- and syn-kinematic leucogranite bodies intruded within the granites and granite gneisses. The foliation-parallel deformed leucogranite sill shows the dextral shear sense in an extensive metamorphic complex that is in concordance with the Karakoram Fault (KF) in the Ladakh region, NW India. Whole-rock elemental and biotite chemistry equivocally suggest subduction-related metaluminous (I-type) calc-alkaline nature for most of the host granites and gneisses, and generation of syn-collisional peraluminous (S-type) leucogranites through crustal anatexis of pre-existing rocks. The obtained U-Pb zircon ages for the granites, granite gneisses, deformed and undeformed leucogranites vary widely from ca. 160 Ma to 15 Ma and reveal: (a) the initiation of subduction of the Neo-Tethyan oceanic crust beneath the southern Asian Plate at least ~160 Ma ago, and (b) existence of continuous or intermittent deformation along ~1000 km long lithospheric scale dextral KF during ~27−15 Ma. [ABSTRACT FROM AUTHOR]

The assembly of Gondwana supercontinent involved multiple stages of continent convergence during the Neoproterozoic including arc magmatism and final collisional metamorphism. Peninsular India occupies a key position in the Gondwana supercontinent assembly where widespread Neoproterozoic magmatic records are preserved. Here, we investigate representative felsic magmatic intrusions from the Achankovil Suture Zone that marks the boundary between the Madurai and Trivandrum crustal blocks. We present petrological, geochemical, and zircon U‐Pb and Lu‐Hf data from the Chengannur (CH) and Pathanapuram (PT) plutons. Petrographic studies on syenogranites from the CH pluton indicate I‐type features, and feldspar thermometry shows ultrahigh temperatures (~1,000°C) corresponding to similar temperatures reported for the surrounding metamorphic rocks. Geochemically, the PT suite displays island arc affinity, whereas the CH suite shows adakitic, oxidized A‐2 type features. In tectonic discrimination plots, the CH samples correspond to volcanic arc granite, whereas the PT samples traverse syn‐collisional granite and volcanic arc granite zones, indicating a transitional feature. Trace element relationships suggest magma fractionation dominantly controlled by plagioclase, K‐feldspar, amphibole, and biotite. Magmatic zircon grains from the CH rocks show upper intercept ages in the range of 783 to 819 Ma and lower intercept ages in the range of 519 to 545 Ma, with cumulative age peaks at 766 and 529 Ma. The combined age population of monzogabbro, granodiorite, and granite from the PT pluton shows distinct peaks at 1,021, 950, and 537 Ma. Zircon grains from the CH pluton show dominantly negative εHf (t) values in the range of −5.8 to −13.4 and yield Hf depleted model age (TDM) ranging from 1,541 to 1857 Ma and Hf crustal model ages (TDMC) of 2,029 to 2510 Ma. In contrast, zircon grains from the PT pluton show dominantly positive εHf (t) values (2.9 to 9.8) with depleted model ages (TDM) in the range of 1,145 to 1434 Ma and Hf crustal model ages (TDMC) in 1,164 to1,686 Ma. The zircon U‐Pb and Lu‐Hf data clearly indicate that the timing of magmatism and magma sources is different for the two plutons, although both witnessed a common metamorphic event during late Neoproterozoic–Cambrian. The PT pluton was emplaced during the early Neoproterozoic with magma source involving mostly juvenile or depleted mantle components, as also attested to by the geochemical signature of arc affinity. In contrast, the CH pluton formed later during mid‐Neoproterozoic with magma from deeper source and dominated by recycled Paleoproterozoic material, which possibly involved depleted mantle components, both associated with an earlier subduction regime. The results reported in our study correlate with those from the arc magmatic rocks in the southern part of the Madurai Block as well as from the crustal blocks in the adjacent terrane of Sri Lanka. The extensive Neoproterozoic arc magmatism in a subduction‐related setting involving both juvenile additions and recycled older components represents the building blocks of Gondwana. [ABSTRACT FROM AUTHOR]

During 2014–16, a semi-permanent network of four 3-component broadband seismographs was operational in the Rajasthan craton and Aravalli mobile belt in the NW Indian shield. The reliable and accurate broadband data from 16 selected regional Indian earthquakes of Mw 5.5–7.8 from this seismic network enabled to estimate the group velocity dispersion characteristics and one-dimensional regional shear velocity structure of northern India, covering the region below north India between the entire Himalaya (from the Pakistan Himalaya in west to the Burmese arc in the east) and Rajasthan (including Aravalli mobile belt). First, Rayleigh- (at 7–87s) and Love- (at 7–82s) wave group velocity dispersion curves were measured and then these curves were inverted to estimate the crustal and upper mantle structure below north India. It is observed that group velocities are of variable nature within the region. This could be attributed to the complex crust-mantle structure in the study region resulted from the magmatism episodes associated with the Proterozoic collision, 65 Ma Deccan volcanism and the Himalayan collision. The best model in the study region reveals a two-layered crust, with a 15-km thick upper-crust (UC) of average shear velocity (Vs) of 3.12 km/s and a 25-km thick lower-crust(LC) of average Vs of 3.44 km/sec. The modeling detects a drop in Vs (∼1-2%) at 79–120 km depths, underlying north India, representing the probable seismic lithosphere-asthenosphere boundary (LAB) at 79 km depth. A geothermal gradient extrapolated from the surface heat flow (∼74 mW/m2) shows that such a gradient would intercept CO2-bearing mantle peridotite solidus at 100 km depth, and thus could signal the presence of small amounts of partially melted magma below 100 km depth. Therefore, this 1–2% drop in Vs could be attributed to the presence of carbonatite melts in the upper mantle related to magmatic episode of 65 Ma Deccan plume activity as also suggested by existing geological and seismological evidence. [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]

• Mid-Neoproterozoic magmatic and sedimentary rocks exposed in the Zhangbaling Uplift. • All the magmatic rocks were characterized by the A-type granites. • The variable geochemical signatures reveal the breakup of Rodinia supercontinent. • The Yangtze Craton should be located in the edge of Rodinia supercontinent. Rocks recording Neoproterozoic geological events related to the Precambrian supercontinent cycle are widely distributed in the Yangtze Craton, and can be used to investigate the evolution of the craton in the context of supercontinent assembly-breakup. However, the paucity of systematic research into Neoproterozoic magmatism and sedimentation in the northeastern Yangtze Craton has hindered our understanding of the evolution of Yangtze Craton. In this study, middle Neoproterozoic magmatic and sedimentary rocks from the Zhangbaling Uplift were analysed to investigate the tectonic development of the northeastern Yangtze Craton and its relationship to the evolution of the Rodinia supercontinent. The results of petrographic and geochronological analyses indicate that the samples record two main stages of silicic magmatism (807–787 Ma granitic gneisses and 757–740 Ma quartz-keratophyres), and that proximal sedimentary rocks deposited at 662 Ma. The granitic gneisses and quartz-keratophyres exhibit the geochemical characteristics of typical A-type granites, with high contents of total-alkalis and HFSEs, suggesting an extensional tectonic setting during their formation. The main residual minerals in the rocks are garnet (gneisses) and plagioclase (keratophyres), reflecting the different depths of partial melting of the source rocks. The gneisses and keratophyres have contrasting zircon Lu-Hf isotopic components (ε Hf (t) = −29.9 to −11.8; −5.8 to 2.5). These lines of evidence imply a crustal structure comprising ancient lower crust and juvenile middle-upper crust. The particular crustal structure is obviously different from adjacent Dabie-Sulu orogenic belt, hinting Zhangbaling Uplift is an in-situ uplift zone. The magmatic evolution recorded by the granitic gneisses and quartz-keratophyres reflects a progression through different stages of continental rifting, from initial extension to mature rifting during the breakup of Rodinia supercontinent. In addition, the prominent affinity between low δ18O magmatism and sedimentation in the Yangtze and India Craton implies that the Yangtze Craton was located on the margin of Rodinia supercontinent prior to breakup. [ABSTRACT FROM AUTHOR]

The fold belts, which border the cratons, are the building blocks for understanding the origin and modification of older continents. The Aravalli-Delhi Fold Belt (ADFB) in northwestern India provides evidence of crustal block accretion due to continental collision, whereas Malani Igneous Suite (MIS) modified with widespread magmatism. Imaging of upper mantle structure and lithospheric modifications, if any, of such regions has been intricate owing to reworking by subsequent superimposed tectono-magmatic processes. We applied a 2D modelling approach to model the lithospheric architecture along a 1000-km long WNW-SSE geotransect across northwestern India, which has been deformed in the past. Our modelling technique combines terrestrial gravity anomaly, heat flow data, satellite-based geoid, and topographic datasets using the basic premise of thermal steady-state and local isostasy. The overall 38 to 40 km thick crustal geometry underneath the Marwar Block had the maximum lithological heterogeneity. The region surrounding the MIS is characterised by 8–10 km thick high-density (2.78 g/cm3) sills deposited in the upper crust down to 9 km depth and another 10–15 km thick high-density (3.05 g/cm3) mafic mantle material near the Moho. About 42 km thick crust, including an 8 to 10-km thick high-density (3.05 g/cm3) underplated layer at its bottom, characterises the high-relief ADFB. The Vindhyan region of Bundelkhand craton is defined by a ∼ 1 km thick trap, having Moho extending at a depth of ∼40 km. The lithospheric thickness varies substantially from ∼143–168 km underneath the Marwar block, which thins to ∼135 km under the ADFB and thickens gradually to ∼150–165 km beneath the Vindhyan region. Substantial crustal density differences in distinct crustal domains, when integrated with the thin lithosphere, reinforce the concept that tectono-magmatic processes might have modified the lithosphere in NW India. [Display omitted] • A typical layered structure indicates no evidence of crustal modification underneath the Bundelkhand craton • Density inhomogeneity in Marwar Block and ADFB corresponds to crustal modification through collision and mafic intrusion. • Thermal perturbations and collisional tectonics are the twin causes of lithospheric modification in northwest India. [ABSTRACT FROM AUTHOR]

This study provides the first record for the emplacement of post-collisional A-type granites in extensional regime during the late Grenvillian period in northwest India. The ca. 970 Ma granites of the Sendra Granitoid Suite (Chang pluton) intrude calc-silicate rocks of the South Delhi Supergroup in the central Aravalli orogen. The Chang pluton is composed of granite sensu stricto; the granites are metaluminous, ferroan, calc-alkalic, and are characterized by high Ga/Al (>2.5), Nb + Y (>60 ppm), Ta + Yb (>6 ppm), REE, HFSE and zircon saturation temperatures, typical of A-type granites. The Y/Nb >1.2 further classified the rocks as A2-subtype, signifying their derivation from crustal sources in a post-collisional setting. The crustal source is also supported by their high LILE (Rb, K and Ba), and Pb, Th and REE. The geochronological data and tectonics of the region indicate that the granites were emplaced about 30 Myr after the Grenvillian collisional orogeny. This scenario likely resulted due to delamination of the lower part of the thickened orogenic lithosphere. These results are expected to have significant implications for the assembly tectonics of the Rodinia supercontinent. [ABSTRACT FROM AUTHOR]

The nature and stratigraphic position of the Beawar gneiss unit (BGU) within the central Aravalli orogen (NW India) remain unresolved. These rocks are currently assigned to the South Delhi Supergroup, assumed to be deposited at 1200–1000 Ma. This interpretation is challenged by new results of petrography, combined with U-Pb dating, Hf isotope analyses of zircon, and whole-rock geochemistry. These data reveal that the BGU consists of both ortho- and paragneisses and that the protoliths were formed and/or deposited at the boundary between the late Paleoproterozoic and early Mesoproterozoic at ca. 1600 Ma. U-Pb ages of detrital zircon grains from a paragneiss sample indicate a maximum deposition age of 1614 ± 14 Ma and major age peaks at 2528, 1916, 1840, 1725, and 1617 Ma. These ages, in combination with Hf isotope data, suggest that the source area consisted mainly of felsic magmatic rocks similar to those exposed within the Aravalli orogen and in the Bundelkhand Craton and/or in terranes within the Central Indian Tectonic Zone. A single detrital zircon with an Eoarchean crystallization age of ca. 3630 Ma and Hf model age of 4.05 Ga point to the existence of the Hadean crust. Magmatic zircon in an orthogneiss sample yields an upper-intercept age of 1581 ± 24 Ma, indicating granite emplacement during the early Mesoproterozoic. Combined geochemical and Hf isotope data suggest that the orthogneiss protolith was a strongly peraluminous S-type granite, formed by melting of surrounding country rocks perhaps within a convergent setting. U-Pb ages (980–960 Ma) of zircon overgrowths and monazite grains suggest that all the rocks were affected by a Grenvillian metamorphic overprint during the assembly of Rodinia. [ABSTRACT FROM AUTHOR]

The Neoarchean Sonakhan greenstone belt (SGB) in the north‐eastern Bastar Craton is mainly composed of an association of pillowed and massive tholeiitic basalts emplaced within an intraoceanic environment. Two types of ultrabasic rocks were identified and are designated as TH‐1 and TH‐2 on the basis of geochemical parameters. Both sample suites exhibit depletion of HFSE with reference to LILE and LREE, LREE/HFSE ratios, and negative Nb–Ta–Ti anomalies in the primitive mantle‐normalized multi‐element diagrams. The geochemical characters of TH‐1 and TH‐2 are consistent with Island arc tholeiites (IAT) and boninite‐like rocks of both Archean and Phanerozoic terranes. Mineral chemistry of clinopyroxenes from both volcanic suites indicate an oceanic arc affinity. The chromite chemistry indicate its derivation from a boninite‐like magma in a suprasubduction zone (SSZ) environment. Trace element modelling depicts that source depletion with significant influence of fluids derived from the subducting oceanic slab collectively controlled the trace element inventory of the mantle wedge, which result to the higher abundance of LREE and LILE compared to HREE and HFSE. The occurrence of lower basalt sequence followed by IAT and boninite‐like rocks in the SGB define a magmatic evolution which is comparable to the Phanerozoic ophiolite suites that exhibit subduction initiation prior to forearc rifting and suprasubduction zone magmatism. The subduction initiation in the intraoceanic lithosphere and the initial decompression melting followed by the upwelling of the MORB‐related magmas were attributed to the formation of the lower pillow basalts. Dehydration of the subducting plate and the melt extraction processes in the hydrous lherzolite mantle wedge account for the formation of TH‐1. Subsequent depletion and significant modification of a more refractory harzburgite source by the slab‐derived fluids generated the TH‐2 rocks. The compositionally diverse magmatic imprints with IAT and boninite affinity in the SGB indicate the significance of episodic melt extraction processes, dehydration of the subducting plate, and hydrous fluxing in SSZ tectonic setting. [ABSTRACT FROM AUTHOR]

The Amba Dongar carbonatite‐alkaline complex is regarded as a late phase intrusion (ca. 65 Ma) associated with Deccan volcanism. Existing age constraints on the Amba Dongar carbonatite are based on phlogopite 40Ar–39Ar plateau ages derived from carbonatite and associated alkaline rocks within the complex. We explore the utility of apatite, a common accessory mineral in Amba Dongar carbonatites, as a petrogenetic and geochronological tool to constrain further the evolution of the carbonatites. Apatite exhibits different crystal forms—from hexagonal stubby prisms to ovoid and elongate grains. Apatite occurs as cumulate and disseminated grains that are either primary, fractured, or recrystallized. SrO content is high in primary apatite (3.17 wt%) but less in recrystallized (1.90 wt%) and disseminated grains (0.47 wt%). MnO and Cl are negligible while FeO is typically low in all samples. SiO2 content is low except for a few primary grains which measure up to 1.35 wt%, correlating with high REE content. LREEs dominate the total REE budget of Amba Dongar apatite, with HREEs below EPMA detection limit in most samples. Total REE content is generally low, though some primary apatite contains up to 3.19 wt% REEs. We also report UPb apatite ages from the carbonatites analysed in situ by LA‐ICP‐MS. The data from all samples combined on a UPb Tera–Wasserburg concordia yield a lower intercept age of 65.4 ± 2.5 Ma (MSWD = 2.8, 207Pb/206Pbi = 0.8272 ± 0.0028), and the Amba Dongar carbonatites are thus interpreted to represent a phase of coeval magmatic activity with Deccan volcanism. [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]

Kimberlite field is an example of widespread Mesoproterozoic intracontinental magmatism. Recent studies have identified deep subcontinental lithospheric mantle as a source region of the kimberlite magmatism while timing, origin, and processes responsible for the generation of coeval lamprophyres remain poorly constrained. Here, we present and discuss new petrological and geochemical data for two lamprophyre dykes from the Wajrakarur kimberlite field and assess their petrogenetic relation to the kimberlite occurrences. Based on mineral compositional and whole‐rock geochemical characters, it is suggested that lamprophyres are formed through low degrees of partial melting of "enriched" lithospheric mantle that was modified and metasomatized by melts derived from recycled crust. This differs from geochemical imprints found in coeval kimberlites, where a crustal source component appears to be absent and is more consistent with rock derivation from "depleted" lithosphere which has experienced interaction with asthenosphere‐derived melts. An apparent lack of garnet in the mantle sources of lamprophyres is suggestive of melting at comparatively shallow depth (~100 km) relative to the kimberlites. Hence, these geochemically contrasting rocks, although have formed at the same time, are derived from vertically heterogeneous lithospheric mantle sources and can be explained through and linked with a thermal anomaly in the underlying convective asthenosphere. We suggest that the deeper mantle source region of the kimberlites was more pristine and devoid of subduction‐related signatures, whereas the shallower mantle source region of the lamprophyres seems to have preserved imprints of plate convergence and subduction associated with the evolution of the Dharwar Craton. [ABSTRACT FROM AUTHOR]

• New 1888 Ma mafic dyke swarm in southwest Yilgarn Craton, Western Australia has been discovered. • The new dyke suite suggests connection with India at ca. 1890 Ma and may be part of the Bastar-Cuddapah Large Igneous Province. • The dyke swarm is coeval with global mafic magmatism found on most other Precambrian cratons. The Archean Yilgarn Craton in Western Australia is intruded by numerous mafic dykes of varying orientations, which are poorly exposed but discernible in aeromagnetic maps. Previous studies have identified two craton-wide dyke swarms, the 2408 Ma Widgiemooltha and the 1210 Ma Marnda Moorn Large Igneous Provinces (LIP), as well as limited occurrences of the 1075 Ma Warakurna LIP in the northern part of the craton. We report here a newly identified NW-trending mafic dyke swarm in southwestern Yilgarn Craton dated at 1888 ± 9 Ma with ID-TIMS U-Pb method on baddeleyite from a single dyke and at 1858 ± 54 Ma, 1881 ± 37 and 1911 ± 42 Ma with in situ SHRIMP U-Pb on baddeleyite from three dykes. Preliminary interpretation of aeromagnetic data indicates that the dykes form a linear swarm several hundred kilometers long, truncated by the Darling Fault in the west. This newly named Boonadgin dyke swarm is synchronous with post-orogenic extension and deposition of granular iron formations in the Earaheedy basin in the Capricorn Orogen and its emplacement may be associated with far field stresses. Emplacement of the dykes may also be related to initial stages of rifting and formation of the intracratonic Barren Basin in the Albany-Fraser Orogen, where the regional extensional setting prevailed for the following 300 million years. Recent studies and new paleomagnetic evidence raise the possibility that the dykes could be part of the coeval 1890 Ma Bastar-Cuddapah LIP in India. Globally, the Boonadgin dyke swarm is synchronous with a major orogenic episode and records of intracratonic mafic magmatism on many other Precambrian cratons. [ABSTRACT FROM AUTHOR]

Uplift of the Tibetan Plateau is thought to be one of the most important orogenic and climate forcing events of the Cenozoic Era, associated with geodynamic changes related to India-Asia collision and subsequent continental lithosphere subduction. However, the fate and scale of the subducted continental lithosphere segments remain highly controversial. Using a comprehensive compilation of the spatiotemporal distribution of postcollisional magmatic rocks across Tibet, together with new geochemical and Sr-Nd-Pb isotopic data and modeling simulations, we propose a holistic, two-stage evolutionary model to explain the link between genesis of the magmas and continental subduction. The magmatism prior to 25 Ma resulted from continuous upwelling of a carbonate-rich upper-mantle plume induced by northward underthrusting of Indian oceanic and continental lithosphere with its cover of Tethyan platform carbonate sediments, whereas magmatism after 25 Ma was related to opposing northdirected and south-directed continental subduction. Our model indicates a transformation in the distribution and nature of the magmatism in Tibet at ca. 25 Ma, which reflects a significant change in the Himalayan-Tibetan orogen and associated mantle dynamic processes in the early Miocene. Understanding this transformation could have important implications for the utility of the Himalayan-Tibetan system as a modern analogue for ancient orogens. [ABSTRACT FROM AUTHOR]

The northward subduction of the Neo-Tethys oceanic lithosphere and subsequent collision between India and Asia continents gave rise to the Tibetan Plateau. However, how and when oceanic subduction started to transform to an intraplate environment are still open questions. The granitoids distributed in Lhasa Terrane of south Tibet offer a unique chance for us to investigate the deep geodynamic processes. Here, we present zircon U–Pb–Hf isotope, whole-rock major and trace element and Sr–Nd isotope data of granitoid intrusions in the Sangsang area of the southern Lhasa Terrane. The Sangsang granodiorites and granites were crystallized at ca. 54 Ma, while the emplacement age of the quartz monzonites is ca. 47 Ma. The granodiorites are characterized by relatively high Mg# values (35.3–41.1) and Fe2O3t (5.16–6.26 wt%) contents, and low Na2O + K2O contents (6.4–6.9 wt%) and A/CNK values (0.91–0.99), which are similar to the geochemical characteristics of I-type, high-K calc-alkaline rocks. They have high 87Sr/86Sri ratios (0.706455–0.706490), and low εNd(t) (− 3.58 to − 2.96) and zircon εHf(t) (− 3.4 to 0.3) values, indicating they were derived from a hybrid source of ancient mafic crust and juvenile lower crust. The coeval granites have lower Mg# values (22.5–27.25) and similar zircon εHf(t) values (− 2.6 to 1.1), suggesting they were probably differentiation productions of the granodiorites. The quartz monzonites have higher Na2O + K2O contents (9.18–9.59 wt%) and A/CNK values (0.98–1.03), higher zircon εHf(t) values (− 2.2 to 2.6) and more depleted Sr and Nd isotopes than the granodiorites and granites. The quartz monzonites were probably produced by melting of mixed juvenile crustal materials and metagreywacke. The new geochronological and geochemical data help constrain the geodynamic processes in the Lhasa Terrane during the Early Cenozoic, as the Sangsang granitoids represent the change from subduction termination to intraplate extension at the southern margin of the Lhasa Terrane. [ABSTRACT FROM AUTHOR]

Abstract Voluminous magmatism at active continental margins and collision zones is marked by I-type intrusions. Paleocene-Eocene intrusions, exposed in the Lhasa terrane of the Tibetan Plateau, are part of the Gangdese arc that operated during Neo-Tethyan ocean subduction and subsequent India-Asia collision. Arc-like geochemical trace element signatures and radiogenic isotope systematics are indicative of juvenile I-type magmatism with variable silica contents consequent to igneous differentiation. Here, we present the first Fe isotope data for this fossil arc terrane, which have highly variable δ57Fe values (relative to IRMM-014) of −0.05 to +0.57‰. The data show no obvious correlations with major and trace element systematics, except for highly evolved rocks with >70 wt% SiO 2. Based on trace element systematics, deuteric fluid exsolution is excluded as a cause for the isotope variations in less evolved rocks. Furthermore, there is no apparent relation between Fe isotope values and the established tectonic evolution from syn - to post-collisional magmatism. Comparison with I-type granites of the Australian Lachlan Fold Belt and Cordilleran Snake River Plain reveals an, on average, lighter δ57Fe in the Gangdese suite in primitive lavas, yet distinctively heavier than intra-oceanic arcs. The heavier δ57Fe values for primitive Lachlan Fold Belt and Snake River Plain rocks are interpreted here as crustal contribution in the form of S-type magmas derived from crustal anatexis, which are absent in the Gangdese arc. Gangdese Belt data yield an average δ57Fe of +0.13 ± 0.02‰ (2σ), which is proposed as the best estimate for juvenile crust at active continental margins. Rhyolite-MELTS modelling suggests that the Gangdese Belt data can be reproduced through fractional crystallization along a liquid line of descent at oxygen fugacity between FMQ = 0 to +2, typical for arc-related melts. Crucially, the majority of data is coherent with partial melts of existing mafic crust as the major contributor to the juvenile component in the intrusions, with minor mantle-derived melts, evidenced through heavier primitive Fe isotopes. This indicates that for the Gangdese Belt samples, the primitive, parental melts are derived from lower crustal successions through predominantly crustal reworking with only subordinate crustal growth. Hence, the Fe isotope data indicates a two-step evolution with melting of underplated mafic material sometime in the geologic past. Although juvenile in nature, these successions are part of the existing crust, supporting scenarios in which crustal reworking in convergent margin intrusions is an important process in evolved magma generation. Highlights • The Paleocene-Eocene Gangdese I-type intrusions have variable δ57Fe values of −0.05 to +0.57‰. • An average δ57Fe value of +0.13 ± 0.02‰ (2σ) is the best estimate for juvenile crust at active continental margins. • Crustal reworking at convergent margins is an important process. [ABSTRACT FROM AUTHOR]

Abstract New geochemical and geochronological data are presented for a suite of metavolcanic rocks from Shimoga greenstone belt to understand their petrogenesis and to constrain the timing of final mafic magmatic activity in western Dharwar craton. We report an Sm-Nd isochron age of 2638 ± 66 Ma for metabasaltic and metaandesitic rocks of the stratigraphically uppermost Medur Formation of Dharwar Supergroup exposed in the belt, which is the youngest age obtained yet for Neoarchean mafic magmatism in western Dharwar craton. The emplacement of the basalt-andesite-dacite-rhyolite suite of rocks took place in a magmatic arc culminating in the deposition of vast greywacke-argillites in a continental margin-type setting. The magmatic precursors of the metavolcanic rocks were generated by partial melting of depleted mantle by slab-derived fluids with variable input from the subducting slab. Assimilation-fractional crystallization processes may also have contributed to the magmas to a significant extent. The younger mafic lithologies of the Dharwar stratigraphy represent accretionary orogens and the date obtained in this study points towards the final stages for the assembly of western Dharwar craton by subduction processes during Neoarchean. The thickness and extent of the greywacke-argillite suite in SGB could be attributed to the protracted deposition during amalgamation of western Dharwar craton with a northern Archean continental crust that might underlie Deccan volcanic rocks. Highlights • 2638 ± 66 Ma Sm-Nd age is the youngest obtained for Dharwar Supergroup mafic rocks. • Medur and Daginakatte formations mark the cessation of greenstone magmatism in WDC. • Younger mafic rocks of Shimoga belt represent Neoarchean accretionary orogens. [ABSTRACT FROM AUTHOR]

Through extensive field studies substantiated by detailed petrographic, geochemical and mineral chemistry studies, a significant event of "Proterozoic magnesian feldspathic magmatism" is reported from the SE part of the Indian subcontinent. Three major granitoids i.e. Vellaturu, Ipuru and Nakerikallu (VIN) are emplaced along an NNE-SSW axis in the Proterozoic Nallamalai fold belt (NFB) in the Eastern Dharwar craton (EDC). The axis of emplacement of VIN granites represents a tectonic contact that is juxtaposed along the NE fringes of NFB and adjoining Precambrian accretionary terrain comprising of gneisses and amphibolites with intrusive granites in the northern part of the Nellore schist belt (NSB). Petrographically the VIN granitoids are biotite ± hornblende bearing with apatite and zircon as accessory phases. Exsolution texture is observed in the form of microcline microperthite intergrowth. In IUGS, QAP diagram the VIN granitoids essentially fall in granite — granodiorite field. Presence of mafic rich microgranitoid enclaves (MMEs) are prominently noticed in the VIN granitoids indicating magma mingling. These granitoids are deformed along their margins. Enclaves of quartzite of NFB and older amphibolites indicate the intrusive nature of VIN granitoids. Major oxide analyses indicate that the Mg# ranges from 43 to 56. Rare earth element studies reveal a general enrichment of LREE relative to HREE. Incompatible HFSE element studies indicate a significant Nb and Ti negative anomaly; characteristic of subduction zone magmatism. In Y + Nb vs Rb trace element tectonic discrimination diagram the granitic rocks of Nakerikallu, Ipuru and Vellaturu essentially fall in post-collisional granites (post-COLG) field. Based on the remarkable magnesian feldspathic character coupled with their emplacement in an arc magmatic tectonic setting, it is concluded that the VIN granitoids in the Proterozoic NFB, SE India; mark a significant event of "Proterozoic magnesian feldspathic magmatism" in the EDC. [ABSTRACT FROM AUTHOR]

Abstract India has perhaps the richest Paleoarchean to Paleoproterozoic crustal components on Earth (Miller et al., 2018). Notwithstanding this, much of the Indian subcontinent remains unexplored compared to other ancient cratons in North America, Australia, Brazil and Africa. There are five Archean cratonic nuclei in India (the Aravalli, Bundelkhand, Singhbhum, Bastar and the Dharwar) with well-preserved Proterozoic supracrustal sequences. This paper critically reviews the Paleoarchean to Paleoproterozoic supracrustal record of the Indian subcontinent with special emphasis on the Archean-Paleoproterozoic transition, which is generally placed at ~2.5 Ga based on the emplacement age of the Great dyke of Zimbabwe. In general, the Archean-Paleoproterozoic transition in Indian cratonic blocks is associated with high continental freeboard condition. Unlike North America, South Africa and Western Australia, the Indian cratonic blocks (except Bastar) are devoid of Paleoproterozoic glacial diamictite (Mazumder et al., 2015). However, similar to the Pongola Supergroup of South Africa, there are evidences of Neoarchean glaciation in Dharwar (Ojakangas et al., 2014). In contrast to the global scenario of extensive development of BIF across the Archean-Paleoproterozoic transition, the Indian Paleoproterozoic successions are devoid of Banded Iron Formation (BIF) (except the 1.85 Ga old BIF in Bundelkhand). In contrast, the majority of the Indian BIFs are of Paleoarchean or Neoarchean age. Thus, the geodynamic and supracrustal data collected from five Indian Archean cratonic blocks do not correspond uniquely and precisely to a global change in tectonic style, onset of Neoarchean global magmatism and rifting, or lithostratigraphic and environmental changes suggested across the Archean-Paleoproterozoic transition (Van Kranendonk et al., 2012). Therefore, a revision and redefinition of the Archean-Proterozoic boundary is outstanding. This article is part of a special issue entitled: Archean Earth Processes; Edited by: Rajat Mazumder and Patrick Eriksson. [ABSTRACT FROM AUTHOR]

Over the past ten years we have numerically modelled the properties of the magmatism generated at four of the key areas where the 'mantle plume-volcanic margin hypothesis' is expected to be valid: the North Atlantic, South Atlantic, India- Seychelles and Afar. Our model incorporates many of the original assumptions in the classic White and McKenzie model, with pure shear of the lithospheric mantle, passive upwelling and decompressional melting. Our model is however two- rather than one-dimensional, can capture the rift history (extension rate changes and axis jumps) and tracks mantle depletion during melting. In all four of our study areas we require the sub-lithospheric mantle to be 100 - 200°C hotter than 'normal', nonvolcanic margins to explain the characteristics of the magmatism. In the three passive margin cases we find this excess temperature is limited to a 50 - 100 km thick layer. We require this layer temperature to drop along-strike away from the proposed sites of plume impact at the base of the lithosphere. However, we also find that lithospheric thickness and rift history are as important as temperature for controlling the magmatism. Our work therefore lends support to the hypothesis that the excess magmatism at volcanic margins is due to a thermal anomaly in the asthenosphere, albeit with consideration of extra parameters. [ABSTRACT FROM AUTHOR]

Frequency distribution (histogram) calculated on the basis of igneous and detrital zircon U-Pb ages has been commonly utilized to interpret the age (range) of magmatic events. The temporal properties revealed by these types of data have also been integrated with other types of isotope data (e.g., neodymium, hafnium, and oxygen) to describe the high magmatic addition rate (MAR) and its association with the growth or reworking of the continental crust. Major peaks are picked to associate with pulses of high-volume magmatic flare-ups related to episodic evolution of continental crust. With the development of modern isotope identification technology which results both in reduction of analytical error of isotope data and rapid accumulation of massive high-quality data, the temporal and frequency variances of these types of data ought to be quantitatively analyzed to study magmatic evolution with respect to tectonic background. A new fractal density concept and a local singularity analysis (LSA) method have been recently and successfully applied to analyze the geometric property of the age peaks in global zircon U-Pb age database by power law models. The anomalies of age peaks identified are linked to deeply rooted avalanches associated with short spurts of convection during formation of supercontinents and continent crust growth. In this paper, the method is further used to analyze a small dataset of U-Pb ages from Gangdese arc to characterize the causational relationship of age peak and India-Asia collision. The results show that the age density around peak at 51 Ma can be fitted by power law functions. Both the scaling range of the age distribution and the exponents of the power law functions observed from the data suggest that the age peak may reflect magmatic flare-ups which would have been caused by superimposing of subduction, exhumation and slab breakoffs. It has been demonstrated that the LSA can be used as a new way to quantitatively characterize magmatic flare-ups based on U-Pb age data from a fractal density point of view. [ABSTRACT FROM AUTHOR]

• Granites in northern margin of Singhbhum Craton belong to Singhbhum Granite Complex. • Zircon and apatite indicate 3257 ± 19 Ma crystallization age for Singhbhum granite. • Detrital zircon and apatite in Bisrampur Formation sourced from Singhbhum Craton. • Bisrampur Formation was deposited on a continental margin during the Mesoarchean. • Terrigenous sedimentation in Singhbhum support Mesoarchean continental emersion. Archean cratons are windows into Earth's early history. The Singhbhum Craton of India preserves an extensive record of Archean magmatism and basin formation events. This study explores magmatism and source-to-sink relationships of the basin in the northern margin of the craton. Magmatic zircon and apatite U-Pb ages from basement granite indicate a mean crystallization age of 3257 ± 19 Ma, with zircon ɛHf (t) values ranging from –2.1 to +1.7 demonstrating the role of crustal melting in magma genesis. Petrographic observations confirm a K-rich composition for this granite. The new data supports correlation of pluton formation to the later phases of the Singhbhum Granite Complex that dominates the craton's exposure. The unconformably overlying Bisrampur Formation accumulated in a terrestrial environment. Detrital zircon U-Pb ages from the formation include unimodal age distributions between 3412 and 3300 Ma, and their ɛHf (t) values range from –1 to +3.4, with the majority (93 %) of grains having positive ɛHf (t) values. The maximum depositional age of the Bisrampur Formation is indicated by the concordia age of 3073 ± 12 Ma calculated from the three youngest zircon ages with similar ɛHf (t) values (+2.6 to +3.3). Detrital apatite ages overlap detrital zircon ages from each sample and include unimodal age fractions between 3450 and 3300 Ma. Detrital apatite trace elements suggest high- and low-grade metamorphic rocks and minor I-type granitoids and mafic igneous rocks in the source region. The new provenance data from the Bisrampur Formation, combined with previous lithofacies and paleocurrent analyses, demonstrate that these terrigenous strata were sourced from the Singhbhum hinterland and deposited during the Mesoarchean. Correlating the Bisrampur formation to other terrigenous successions in the Singhbhum Craton with well-constrained depositional ages, supports previous hypotheses of craton-wide emersion during the Mesoarchean. [ABSTRACT FROM AUTHOR]

Tectonic setting and crustal evolutionary processes recorded in the Meso–and Neoarchaean crust in the northwestern margin of the Dharwar Craton are discussed in this paper based on the geochemistry of 2.97 Ga granite from Kumta-Manjuguni-Kakkalli (KMK) and ≤ 2.65 Ga trondhjemite to granite near Ramnagar-Khanapur (RK). Both the plutonic suites are potassic (total alkalies∼8.9%), high in silica (SiO 2 ∼ 71.9 wt%), and metaluminous to weakly peraluminous. The granite from KMK is characterized by moderately fractionated rare earth elements (REE) pattern (La n /Yb n < 14), unfractionated heavy rare earth elements (HREE) and significant negative Eu/Eu* anomalies (0.2–0.7). The RK granite has fractionated LREE/HREE (20–41) with Eu/Eu* of 0.6–1.07 while the trondhjemite and granodiorite have LREE/HREE of 25–33 and Eu/Eu* between 0.67 and 0.74. The geochemical characteristics of KMK granite suggest derivation from intracrustal melting of TTG type crust and metasedimentary rocks whereas RK granite was derived predominantly from intracrustal melting of felsic crust and high -K basaltic rocks. While the RK trondhjemite was generated from the partial melting of metabasalt. Integration of the present data with those of other granitoids of the WDC indicates a five stage crustal growth, whereby K-rich KMK granite magmatism represented an early crust building cycle with crustal consolidation at ∼3.0 Ga, while the RK granitoids represent the younger and main orogenic cycle at 2.65–2.50 Ga. A similar style of episodic multi-stage crustal growth during the Archaean was common in major cratons globally involving plate convergence and accretion events and supercontinent amalgamation. [Display omitted] • The present data on granitoids of the Western Dharwar Craton (WDC) indicates a 5 stage crustal growth. • 2.973 Ga K-rich magmatism in WDC concluded an early orogenic cycle with crustal consolidation. • 2.65Ga magmatism represents the younger and main orogenic cycle at 2600-• 2500 Ma. • A thickened crust in WDC is indicated by the petrogenesis of 2.65Ga granitoids. [ABSTRACT FROM AUTHOR]

The initial collision between Indian and Asian continents marked the starting point for transformation of land-sea thermal contrast, uplift of the Tibet-Himalaya orogen, and climate change in Asia. In this paper, we review the published literatures from the past 30 years in order to draw consensus on the processes of initial collision and suturing that took place between the Indian and Asian plates. Following a comparison of the different methods that have been used to constrain the initial timing of collision, we propose that the tectono-sedimentary response in the peripheral foreland basin provides the most sensitive index of this event, and that paleomagnetism presents independent evidence as an alternative, reliable, and quantitative research method. In contrast to previous studies that have suggested collision between India and Asia started in Pakistan between ca. 55 Ma and 50 Ma and progressively closed eastwards, more recent researches have indicated that this major event first occurred in the center of the Yarlung Tsangpo suture zone (YTSZ) between ca. 65 Ma and 63 Ma and then spreading both eastwards and westwards. While continental collision is a complicated process, including the processes of deformation, sedimentation, metamorphism, and magmatism, different researchers have tended to define the nature of this event based on their own understanding, an intuitive bias that has meant that its initial timing has remained controversial for decades. Here, we recommend the use of reconstructions of each geological event within the orogenic evolution sequence as this will allow interpretation of collision timing on the basis of multidisciplinary methods. [ABSTRACT FROM AUTHOR]

There exist three mainstream opinions regarding the timing of the initial collision between the Indian and Eurasian continents, namely, 65±5, 45±5, and 30±5 Ma. Five criteria are proposed for determining which tectonic event was related to the initial collision between India and Asia: the rapid decrease in the rate of plate motion, the cessation of magmatic activity originating from the subduction of oceanic crust, the end of sedimentation of oceanic facies, the occurrence of intracontinental deformation, and the exchange of sediments sourced from two continents. These criteria are used to constrain the nature of these tectonic events. It is proposed that the 65±5 Ma tectonic event is consistent with some of the criteria, but the upshot of this model is that the magmatic activity originating from the Tethyan subduction since the Mesozoic restarted along the southern margin of the Asian continent in this time after a brief calm, implying that the subduction of the Neotethys slab was still taking place. The magmatic activity that occurred along the southern margin of the Asian continent had a 7-Myr break during 72-65 Ma, which in this study is interpreted as having resulted from tectonic transformation from subduction to transform faulting, indicating that the convergence between the Indian and Asian continents was once dominated by strike-slip motion. The 30±5 Ma tectonic event resulted in the uplift of the Tibetan Plateau, which was related to the late stage of the convergence between these two continents, namely, a hard collision. The 45±5 Ma tectonic event is in accordance with most of the criteria, corresponding to the initial collision between these two continents. [ABSTRACT FROM AUTHOR]

[Display omitted] • Juvenile crust in Singhbhum Craton formed at ∼3.51, ∼3.45, 3.38–3.25, 3.15–3.05 and ∼2.80–2.75 Ga. • Reworking of older crust in the craton occurred at ∼3.46, ∼3.3, ∼3.1 and ∼2.8 Ga. • Maximum crustal thickness was attained at ∼3.3 Ga followed by a possible reduction over ∼3.1–2.8 Ga. • Paleo-Meso–Archean continental growth occurred through episodic intraplate juvenile magmatism and resultant crustal reworking. The composition of continental crust and its temporal variation, the mechanism of crust-mantle interaction, and the degree of mantle depletion during the early Archean have been widely debated. To address these issues related to the Singhbhum Craton, we present whole-rock sediment geochemistry, detrital zircon U-Pb date, trace element and Hf isotope data from four Archean clastic sedimentary successions. The rocks have high whole-rock K 2 O/Na 2 O, relatively high La and Th compared to Ni and Sc, distinct negative Eu anomaly and flat HREE patterns, and high detrital zircon U/Yb ratios. These features suggest attainment of early crustal stability with the sediments derived from a strongly weathered basement dominated by granitoids formed through shallow intracrustal melting. Detrital zircon U-Pb and Hf isotope data indicate episodic crust formation at ∼3.51, ∼3.46, 3.38–3.25, 3.15–3.05 and ∼2.80–2.75 Ga. Each major crust formation event is marked by addition of depleted mantle-derived juvenile crust and its quick reworking. Besides, episodic tapping of older crust, as indicated by a wide range (both positive and negative) of zircon εHf t values, are evident at ∼ 3.46, ∼3.3, ∼3.1 and ∼2.8 Ga. Pressure-sensitive zircon trace element ratios suggest that the crust attained the maximum thickness at ∼3.3 Ga followed by a possible reduction in thickness over ∼3.1–2.8 Ga. In the absence of strong evidence of subduction, the rock association and their temporal distribution (coeval granitoid and mafic-ultramafic magmatism) suggest that the Paleoarchean-Mesoarchean crustal growth in the Singhbhum Craton was a result of episodic, depleted mantle-derived, intraplate magmatic injection and attendant crustal reworking. [ABSTRACT FROM AUTHOR]

Kaolinite associated with Mesozoic sediments of Kachchh and alkaline igneous rocks are not well studied in view of its genesis. The petrography, EPMA and DTA studies support that the studied kaolinite samples formed by mature transformation from rhyolitic tuff by hydrothermal alteration in epithermal condition. Such postulation indicates that there was intermittent acid volcanic episode along with alkaline basic igneous magmatism in the Cretaceous of Kachchh basin, western part of India. [ABSTRACT FROM AUTHOR]