The eastern margin of the Paleo-Mesoarchean Singhbhum Craton records multifaceted magmatism, including the spatially linked Mayurbhanj granophyre-granite suite and gabbro-anorthosite complexes. The petrogenetic evolution of the granophyre-granite suite remains poorly understood due to the limited availability of geochronological and geochemical data. These rocks are characterized as high-K, calc-alkaline, metaluminous to weakly peraluminous compositions with K2O/Na2O between 1.03 and 1.91. They exhibit moderately fractionated rare earth elements (REEs) patterns with light-REEs (LREEs) enrichment, negative Eu-anomalies, and flat heavy-REEs (HREEs) patterns. Distinct negative Sr, Nb, Ta, and Ti anomalies are evident in the normalized multi-element diagram. Trace element modelling suggests that fractional crystallization of a granodioritic melt controlled dominantly by plagioclase crystallization can reproduce the granophyre-granite melt. Based on their highly ferroan composition, Ga/Al ratios, and other trace element characteristics, the granitoids are classified as crust-derived A-type. The granophyric texture indicates undercooling achieved through the rapid emplacement of granitic melts at a shallow depth. This is corroborated by Zr-saturation geothermometry and Al-in-hornblende geobarometry, which suggest that granitoids crystallized between c. 756 and 940 °C under low pressures (3–6 kbar) corresponding to depths of c. 12–21 km. Zircon U-Pb ages date the emplacement of the granophyre between c. 3096 and 3128 Ma, synchronous with the emplacement of coarse-grained granites at c. 3084–3109 Ma. The Mayurbhanj granophyre-granites are possibly derived from a magma with significant contribution from a crustal source, most likely the Paleoarchean Singhbhum crystalline basement crust. Intracrustal reworking of pre-existing TTG crust in a post-collisional setting offers a viable formation mechanism for the granophyre-granites. Alternatively, their overlapping emplacement ages, similar trace element ratios (e.g., Th/Nb, Gd/Yb, Gd/La), and Nd isotopic compositions with the gabbro-anorthosite suite suggest a cogenetic origin. Combined with shock metamorphic features reported in the nearby Simlipal Complex and shallow-level melting of a crystalline basement (granite + greenstone) source inferred for the granophyres, these suites may have formed from the differentiation of a bolide impact melt, with the gabbro-anorthosite representing the more primitive endmember.

The Palaeoproterozoic Betul belt of central India records bimodal volcanism, with rhyolites hosting Zn-Cu and Zn-Pb-Cu volcanogenic massive sulfide (VMS) deposits. Two rhyolite variants are recognized: foliated biotite/ hornblende-rich rhyolite and massive quartz-porphyritic rhyolite. Field relationships, petrography, and drilling data reveal that the foliated rhyolite is pervasively hydrothermally altered and mineralized, whereas the massive rhyolite remains comparatively fresh and barren. Geochemically, foliated rhyolite exhibits peraluminous and magnesian character, while massive rhyolite is calc-alkaline, metaluminous, and ferroan. Both types of rhyolites display weakly fractionated REE patterns with pronounced negative Nb-Ta anomalies. Their contrasting geological and petrochemical signatures highlight differences in magmatic conditions and metallogenic potential. Tectonic discrimination indicates a post-orogenic (A(2)-type) affinity, with emplacement linked to an arc-back-arc extensional regime. LA-ICP-MS U-Pb zircon dating identifies two distinct magmatic pulses: foliated rhyolites emplaced between similar to 1.72-1.66 Ga, and massive rhyolites between similar to 1.66-1.57 Ga. The earlier, hydrous rhyolitic pulse is spatially and temporally associated with VMS mineralization, coinciding with the global similar to 1.70 Ga magmatic-metallogenic peak during Columbia supercontinent assembly. In contrast, the later, more anhydrous rhyolitic pulse produced largely barren massive rhyolites. The Betul belt thus represents an important Indian analogue to globally significant Paleoproterozoic VMS provinces associated with the evolution of the Columbia supercontinent.

Crustal melting is a fundamental process governing the long-term evolution of continental crust and the formation of tonalite-trondhjemite-granodiorite (TTG) suites and granitic rocks. In the eastern Vinjamuru Domain of the Nellore Schist Belt (SE India), centimetre-scale, garnet-bearing tonalite leucosomes occur within amphibolite (matrix: amphibole + plagioclase + biotite, rare ilmenite; garnet absent) that possesses a steeply-dipping (N-striking) tectonic foliation. These foliation-parallel, podiform leucosomes (<5 vol% of rock) contain garnet porphyroblasts with chemically homogeneous cores with inclusion trails oblique to the foliation, overgrown by chemically-zoned and inclusion-poor rims. Mineral textures indicate low-degree, incongruent hydrous melting of amphibole + biotite + plagioclase + quartz + fluid, producing garnet (Grt-I-core) and melt represented by plagioclase + quartz. Melt-reintegrated phase equilibria modelling reveals that partial melting began at similar to 8.2 kbar and similar to 675 degrees C, with peak metamorphic conditions of similar to 8-9 kbar and similar to 780-810 degrees C. Later inclusion-poor garnets (Grt-I-rim and Grt-II) record late-stage growth during cooling (similar to 9.5-10.2 kbar and similar to 670-680 degrees C) from residual melts, followed by subsolidus re-equilibration. The melts escaped from the system in two stages, evolving from early hydrous tonalitic-granodioritic (similar to 65 wt% SiO2, similar to 11 wt% H2O) to more differentiated granitic (similar to 67 wt% SiO2, similar to 7.5 wt% H2O) compositions, consistent with TTG-like compositions. Electron Backscatter Diffraction (EBSD) data reveal a strong crystallographic preferred orientation (CPO) in amphibole but weak CPOs in plagioclase and quartz, indicating strain partitioning and the fabric development under melt-present conditions rather than by solid-state dislocation creep. U-Pb zircon geochronology constrains an earlier pre-migmatisation tectonothermal event at similar to 1673 +/- 10 Ma. In contrast, titanite grains hosted within leucosomes determine the timing of partial melting and peak metamorphism at similar to 1448 +/- 31 Ma. These results highlight the role of amphibolite-facies partial melting and deformation in the generation of TTG-like melts and reworking of Paleoproterozoic continental crust.

The 87Sr/86Sr composition of apatite from carbonatites and associated silicate rocks can provide important petrogenetic constraints. This study reports for the first time, in situ 87Sr/86Sr composition of fluorapatite from calcite carbonatite, nephelinite, and phonolite from the Kamthai and Amba Dongar complexes, along with their major and trace element compositions. It also reports for the first time, U–Pb ages of apatite in phonolite from the Kamthai complex. Most fluorapatite are oscillatory-zoned, occurring as cumulates or disseminated crystals in the groundmass. Apatite grains from Kamthai carbonatites are distinctly enriched in Sr (2.26–4.08 wt %) and $\Sigma $REE+Y (0.87–1.82 wt %), and depleted in CaO than those in phonolites (0.25–2.28 wt %; 0.17–0.86 wt %), which suggests that Sr and REE substituted for Ca. The similar 87Sr/86Sr of fluorapatite from carbonatite (0.70425–0.70442) and phonolite (0.70381–0.70537) indicates that both were derived from a common parental magma and shared a common source. These results and the association with phonolites strongly suggest that the carbonatites may have formed by liquid immiscibly from a parental phonolitic melt. The limited Sr isotopic variability in fluorapatite of phonolite can be explained by the assimilation of felsic rocks of the Proterozoic Malani Igneous Suite (MIS; 8–15%) or by Archean banded gneisses (BGC; <3%) of the Aravalli Delhi Belt. However, crustal assimilation even up to ~30% of MIS-like or ~ 20% of BGC-like crust, does not affect the 87Sr/86Sr of carbonatites, which reflects the characteristics of its enriched mantle source. Fluorapatite from Amba Dongar rocks has lower concentrations of Sr (0.35–2.06 wt %), $\Sigma $REE+Y (0.37–1.12 wt %), and other incompatible elements compared to those from Kamthai. A positive correlation of $\Sigma $REE with SiO2 in fluorapatite from nephelinite is suggestive of substitution of Si4+ + REE3+ for P5+ + Ca2+, possibly because of elevated silica activity due to crustal assimilation. The 87Sr/86Sr of fluorapatite (0.70532–0.70578) and calcite (0.70558–0.70589) from carbonatite and nephelinite (0.70590–0.70669) are distinct from each other and more radiogenic than those of Kamthai. Approximately 20% assimilation of basement gneisses by a parental magma having 87Sr/86Sr similar to apatite of carbonatites can explain the more radiogenic 87Sr/86Sr ratios of fluorapatite from the nephelinite. The trace element and Sr isotope variations suggest that the mantle source for the Kamthai rocks was more enriched than that for the Amba Dongar rocks. Trace element modeling using apatite–melt partition coefficients suggests that carbonatite and alkaline silicate melts in both complexes are compositionally different and derived from different parental melts. The silicate rocks formed from parental melt, similar to basanite of the Deccan LIP. Uranium–Pb ages of fluorapatite from Kamthai phonolite (64 ± 12 Ma) indicate that it is contemporaneous with the Deccan flood basalts and can, therefore, be linked to the Deccan–Réunion mantle plume.

The Chhotanagpur Granite Gneiss Complex (CGGC) is an integral part of the Central Indian Tectonic Zone (CITZ), which records the Proterozoic tectono-thermal evolution of the Indian Shield. In this study, we carried out detailed petrography, bulk rock geochemistry, Nd isotopic studies and U-Pb zircon geochronology for granitoids from the southwestern CGGC. Four episodes of granitic magmatism from this area are documented, which are (i) c. 1660 Ma granite gneiss, (ii) c. 1565 Ma foliated granite, (iii) c. 1462 Ma porphyritic granite, and (iv) c. 1140 Ma equigranular granite. The c. 1660 Ma granite gneisses are migmatitic, I-type, and their Nd isotopic compositions are mildly sub-chondritic (epsilon Nd(t) = -0.90 to-2.55). The geochemical characteristics suggest them sourced from mafic to intermediate sources with inputs from pre-existing crustal rocks. The c. 1565 Ma foliated granites are peraluminous, S-type, and have evolved Nd isotopic composition (epsilon Nd(t) = -2.40 to-4.69) with Mesoarchean model ages, which suggests their derivation from a metasedimentary source. The c. 1462 Ma porphyritic granite and c. 1140 Ma equigranular granites have geochemical attributes similar to the A2-type granites. The strongly evolved Nd isotopic signatures (epsilon Nd(t) = -4.39 to-5.38 and-6.81 to-8.38) for porphyritic granite and equigranular granite, respectively, suggest inputs from both enriched mantle and pre-existing crustal sources. Based on these findings, the Proterozoic evolution of the CGGC can be broadly divided into four stages, with stages 1 and 2 corresponding to c. 1660-1565 Ma arc magmatism, where the granite gneisses were emplaced, followed by the emplacement of foliated granites in the waning stage. Stage 3 corresponds to the emplacement of c. 1462 Ma A-type granites associated with the extensional environment. Stage 4 is associated with post-collisional setting where the c. 1140 Ma equigranular granites were formed. The presence of recrystallized zircon domains with c. 900-1000 Ma in all granitoid variants supports widespread Grenvillian highgrade metamorphism in the CITZ. These results suggest that granitoids from the southwestern CGGC exhibit a transitional tectonic regime with an initial arc followed by extensional tectonics, culminating in a post-collisional environment, possibly linked with the breakup of Columbia and the amalgamation of Rodinia supercontinents.

The Proterozoic Betul Belt is an important supracrustal unit that records the protracted history of crustal accretion and growth in the Central Indian Tectonic Zone (CITZ). Here, we present results from systematic geological mapping, petrological, geochemical (including Sm-Nd isotope) studies, and U-Th-Pb geochronology on rocks from the Betul belt, with the objective of reconstructing its Proterozoic evolution and its link with past supercontinents. The Betul belt comprises ca. 2167 +/- 11 Ma granite gneisses, ca. 2051 +/- 80 Ma mafic volcanics (pillowed lava), 1715 +/- 10 Ma rhyolite, and older granitoids (1671 +/- 29 Ma) that have undergone multi-stage deformation and amphibolite-facies regional metamor-phism. The bulk rock geochemistry of gneisses, pillow lava, and mafic intrusions are characterized by arc -like signatures, whereas the rhyolite and granites are anorogenic and back-arc related. The whole-rock geochemical and Sr-Nd isotopic compositions of pillow lavas and mafic intrusions suggest the involve-ment of recycled crustal material in their source, possibly in the form of associated sediments. The Betul granite gneisses were emplaced at 2167 Ma in a collisional setting by melting crustal protoliths having an affinity with the Bundelkhand craton and may constitute the basement for the supracrustal sequence. The supracrustal units, i.e., mafic volcanics and rhyolites, occur as a bimodal suite formed in the arc and back-arc environment with penecontemporaneous sedimentation. Bulk rock geochemistry and age data indicate two phases of A-type granite magmatism at 1674 Ma and 1079 Ma, with post-collisional geochemical traits forming within an anorogenic and back-arc setting, respectively. Younger post-orogenic granites (Navegaon) were emplaced in a back-arc setting at ca 1079-954 Ma, synchronous with a collisional event in the Sausar belt. Spot ages from monazite in Hbl gabbro yield a weighted mean of 1026 +/- 97 Ma (MSWD = 0.15), reflecting Grenville-age regional metamorphism in the CITZ. The geo-logical events recorded in the rocks of the Betul belt between ca 2167 Ga and 954 Ma correlate well with events that affected Laurentia, Baltica, Australia, and East Antarctica within the frameworks of the Columbia (ca. 2.1-1.7 Ga) and Rodinia (ca.1.2-0.9 Ga) supercontinents.(c) 2023 International Association for Gondwana Research. Published by Elsevier B.V. All rights reserved.

The combination of U-Pb zircon ages with Hf-Sr-Pb isotopes of different intrusive and extrusive felsic and sedimentary rocks provides constraints on the petrogenetic evolution of the continental crust in the western Dharwar Craton, India. The oldest detrital zircon preserved formed at-3.6 Ga and represents a relic of the oldest felsic crustal material in the region. The dominant granitoid units of the western Dharwar Craton contain zircon grains with magmatic ages between 3.4 Ga and 3.0 Ga that indicate the formation of major felsic continental crust during this interval.Trace element abundances of the granitoids indicate that the oldest members of the intermediate to felsic suite derived by partial melting of mafic material at-3.6-3.4 Ga. The initial bulk rock Hf isotope compositions of these granitoids are consistent with their formation by melting of even older mafic material that was slightly enriched relative to the depleted mantle composition. This mafic and slightly enriched material formed by mantle melting at -< 3.8 Ga. The Hf isotope compositions of individual zircon grains, obtained by two different analytical techniques (in-situ and complete dissolution followed by chromatographic separation) give evidence for the presence of such older mafic material (<3.8 Ga) that formed the immediate precursor of their granitoid host rocks. Such a mafic source for the granitoids is consistent with Pb-Sr isotope systematics of these that shows no indication of Eoarchean enriched/evolved material in the western Dharwar Craton. The mafic source material of the granitoids thus represents an intermediate stage of crust formation that started after 3.8 Ga with the formation of mafic crust by mantle melting. The combined geochronological and isotopic constraints suggest that the Mesoarchean felsic crust of the Dharwar Craton formed by differentiation of melts derived from an amphibolite/eclogite source rock and included increasing contributions of reprocessed crustal material with time from-3.6 to 3.0 Ga. The major interval of growth of felsic continental crust was from 3.4 to 3.0 Ga. The younger generation of granitoids formed mostly by reworking of older intermediate to felsic crust. These different felsic magmatic bodies with distinct petrogeneses and sources, that include the depleted mantle, older mafic crust and the evolved continental crust, became essential elements of the stable continental crust of the western Dharwar Craton, the majority of which was generated from 3.4 to 3.0 Ga.

In this study, textural relations coupled with mineral chemistry of hydrothermal magnetite, fluorapatite, monazite and allanite from the Mohuldih uranium deposit in the Singhbhum Shear Zone (SSZ) is used to characterize the nature of the fluid during various events of alteration and uranium precipitation. These minerals have two distinct textural types, the earlier of which are coeval with the uraninite mineralization. The later type formed during subsequent hydrothermal overprint as a result of coupled dissolution‐reprecipitation of earlier fluorapatite and mobilization of light rare earth elements. Uranium‐lead dating of texturally‐constrained hydrothermal monazite grains yields two major concordant age clusters at 1855 ± 7 Ma and 963 ± 10 Ma and several discordant analyses. Two spot analyses furnish concordant ages of 1656 ± 33 Ma and 1438 ± 35 Ma that are identical within error of the 207Pb/206Pb ages (1628–1643 Ma and ca. 1392 Ma) of several discordant data points. Similar ages have been reported by other studies from the rocks of the SSZ and are therefore considered to be geologically meaningful. The oldest age of ca. 1855 Ma obtained from the texturally early core regions of monazite corresponds to the earliest stage of uraninite mineralization. The two main alteration types can be interpreted based on the known metamorphic events in the SSZ. A combination of high‐temperature calcic iron ± sodic and high‐temperature potassic iron alteration accompanied the M1 metamorphic event and the low‐temperature silicification/K‐Al alteration during the M2 metamorphic event. A comparative study between our data on magnetite and fluorapatite compositions with those from global iron oxide‐Cu‐gold (IOCG) and iron oxide‐apatite deposits classifies Mohuldih as an IOCG‐type deposit.

dewashish@gg.iitkgp.ac.in The Western Dharwar Craton (WDC) hosts a typical Archean association of grey gneisses, potassic granites, and greenstone belts. A number of studies [1] have argued for N-S metamorphic gradient across the craton with the metamorphic grade increasing from greenschist facies conditions (4–5 kbar and 400–500°C) in the north, through amphibolite facies condition (5–8 kbar, 600– 640°C) in the central part (Holenarsipur), to granulite facies conditions (8–10 kbar, 700–750°C) near the southern margin (Sargur belt). This led to suggestions that the craton exposes a tilted crustal section with lower crustal levels exposed towards the south. However, the major structural fabric of the craton including the orientation of the greenstone belts and major shear zones is broadly N-S [2, 3]. Uranium-Pb ages from detrital zircon in quartzite/metapelite from the Sargur belt furnish ages between 3.64 Ga and 2.69 Ga [4], while in-situ formed metamorphic zones cluster at c. 2.57 Ga and 2.48 Ga, which suggests that the southern part of the craton underwent high-grade metamorphism in the late Neoarchen and early Paleoproterozoic. In contrast, the regional high-grade tectonothermal overprint in the central part of the craton has been dated at 3.14–3.11 Ga [5], with little evidence for the 2.57–2.48 Ga overprints in the zircon age record [4]. Given the temporal differences in the timing of major high-grade metamorphism in the northern and southern parts

Considerable debate exists on when a persistent depleted mantle reservoir came into existence and whether the Hadean and Eoarchean mantle were depleted.The U-Pb-Hf isotope composition of zircon can be used to track the record of continental crust extraction and resulting mantle depletion.Detrital zircon grains from the Western Dharwar Craton define notable clusters at 3685-3638 Ma, 3573-3524 Ma, 3471-3411 Ma, 3373-3341 Ma, 3277-3249 Ma, 3172-3148 Ma, 3084-2996 Ma, and 2659-2647 Ma which correspond to major episodes of granitoid crust formation in the craton.These zircon grains therefore preserve a continuous record of crust building from Eoarchean to the Neoarchean.The zircon suites furnish both radiogenic (positive) and crust-like (negative) Hf isotopic compositions.Noteworthy is the fact that the εHf (t) of zircon older than 3.6 Ga, i.e., those derived from Eoarchean granitoids generally scatter around chondritic composition (-2.8 to +2.2).At the Eoarchean-Paleoarchean boundary, there is a shift in the εHf (t) of the detrital zircon to strongly positive as well as negative values.This transition can be explained by a distinct change in the source of the granitoids at ca. 3.6 Ga.The Eoarchean granitoids were either derived from juvenile sources extracted from a primitive mantle, or their protoliths had long crustal residence times.In contrast, the Paleoarchean and younger granitoids appear to have been sourced both from strongly depleted mantle-derived sources as well as crustal components that incubated for a long period prior to granitoid extraction.The mantle depletion event must have happened in the Hadean/Eoarchean to allow sufficient time for the depleted mantle reservoir to acquire the strongly radiogenic isotopic compositions by the beginning of the Paleoarchean.

In this study, we use the U-Pb-Hf isotope composition of detrital zircon in metasedimentary rocks from the Western Dharwar Craton to identify older crusts, their nature, source, timing of extraction, and reworking. The samples come from the Holenarsipur region in the central and Sargur region in the southern part of the craton and belong to both the Sargur and the Bababudan Groups. Both detrital and metamorphic domains were identified in the zircon. The metamorphic overgrowths correspond to two age populations at 2536-2516 Ma, and 2478-2460 Ma. Rutile grains provide either concordant 2453 Ma, or discordant younger ages suggestive of thorough re-equilibration during metamorphism. Detrital zircon grains define notable clusters at 3685-3638 Ma, 3573-3524 Ma, 3471-3411 Ma, 3373-3341 Ma, 3277-3249 Ma, 3172-3148 Ma, 3084-2996 Ma, and 2659-2647 Ma which correspond to major episodes of granitoid crust formation in the craton. Based on detrital and metamorphic zircon populations, deposition of both the older Sargur Group and the basal unit of the younger Bababudan Group in the Holenarsipur region were broadly contemporaneous after c. 3160 Ma, while the sediments of the purported Sargur Group in the Sargur region were deposited after c. 2650 Ma. The new age data requires revision of the stratigraphic positions of the Sargur-type and Dharwar-type greenstone belt successions. The detrital zircon suites have both radiogenic and crust-like Hf isotopic compositions. However, the majority have radiogenic compositions that were acquired during major events of juvenile crust extraction between c. 3850 Ma and 3250 Ma. Strongly unradiogenic epsilon Hf(t) of some Paleoarchean detrital zircon require protoliths extracted from the mantle in the Hadean, but which persisted for a long period and contributed to granitoid formation in the Paleoarchean and the Mesoarchean. Mixing of juvenile magmas with preexisting crustal components also played a significant role in the petrogenesis of the granitoids. A distinct shift in the epsilon Hf-(t) of the detrital zircon from chondritic to positive value at c. 3600 Ma is noted, reflecting a marked increase in the contribution of strongly depleted mantle reservoir to the source of the post-c. 3600 Ma granitoids.

The Bastar Craton is one of the oldest cratonic nuclei of the Indian shield, comprising Paleoarchean to Mesoproterozoic crust that preserves the record of protracted crustal evolution and metallogeny. This study describes whole-rock geochemistry, U-Th-Pb ages of zircon and monazite from Neoarchean TTGs, sanukitoids, and Paleoto Mesoproterozoic granites, and Sm-Nd isotope data from mafic enclave within TTGs of the Western Bastar Craton (WBC). The TTGs and sanukitoids represent Neoarchean crust formed by collision-accretion processes. The TTGs are of two types: low-HREE and high-HREE with both groups derived from low-K mafic sources. The sanukitoids have moderate SiO2 (55.1-65.1 wt%, average = 61.7 wt%), Mg# (20-36, average = 24.7), Ni (10-40 ppm; average = 14 ppm), Sr (339-528; average = 418 ppm) and moderate to high concentrations of incompatible elements like Rb (26-112 ppm, average = 48), Ba (482-2300 ppm, average = 1542), Zr (69-593 ppm, average = 334 ppm), Nb (3.8-14.8 ppm, average = 8.7 ppm), Y (13.2-24.5 ppm, average = 19.5 ppm), and REE (91-301 ppm, average = 212)]. They post-date TTG emplacement and formed by mixing between metabasalt-derived and mantle wedge-derived melts in an arc environment. The Mul granite represents a younger Paleo- to Mesoproterozoic suite of granites that was derived by reworking of pre-existing crust. U-Pb ages of zircon constraints the TTG magmatism to 2544-2496 Ma, while Nd-model ages (3259-3142 Ma) of mafic enclaves within the TTG suggest the presence of Paleoarchean crust in the WBC. Zircon and monazite ages indicate that the emplacement of the Mul granite was synchronous with 1666-1547 Ma regional tectonothermal event. These granites were produced by reworking of older granitoid crust. The Neoarchean TTGs/sanukitoids were affected by 1666-1547 Ma tectonothermal event which constitutes a widely documented Paleo- to Mesoproterozoic orogeny in the Central Indian Tectonic Zone and Bhopalpatnam granulite belt to the south of the WBC. Copper and gold mineralization in the Thanewasna belt along the craton's western margin is linked to this tectono-magmatic event. In the global supercontinent outlook, the WBC preserves the imprints of Neoarchean events related to the Ur supercontinent as well as Paleo-Mesoproterozoic and Neoproterozoic (Grenville-age) events associated with the Columbia and Rodinia supercontinent

Charnockites constitute an integral component of granulite belts exposed on the northern and southern flanks of the Godavari rift, which marks the contact between the Bastar and Eastern Dharwar aatons in peninsular India. In this study, we attempt to constrain the petrogenesis of granulites from Gondpipri. Bhopalpatnam on the northern flank and Karimnagar on the southern flank of the Pranhita-Godavari valley using petrography, mineral and whole-rock geochemistry, fluid inclusion studies, and U-Pb zircon geochronology. The presence of relict magmatic textures and orthopyroxene chemistry is suggestive of an igneous protolith while CO2-rich fluid inclusions in quartz correspond to subsequent granulite-facies overprint. Geochemically, chamockites from both granulite belts are metaluminous, magnesian, and talc-alkaline, having similar Sr and Y concentrations, Rb/Sr, Sr/Y, La-N/Sm-N, Gd-N/Yb-N, and Eu/Eu* ratios, and positive Bo-Ph and negative Nb-Ta-Ti anomalies. Zircons in charnockites from both granulite belts furnish magmatic crystallization ages of similar to 2.5 Ga (U-Pb isotope) and also record a metamorphic overprint at ca. 2473 Ma. The similarity in protolith composition and U-Pb ages of zircons in charnockites on the northern and southern flanks of the Godavari rift suggest that they constitute a cogenetic and coeval suite emplaced at -2.5 Ga in an undivided and continuous Palaeo-Mesoarchean land-mass that included the Bastar and Eastern Dharwar cratons, possibly as a part of the Ur-supercontinent. This undivided landmass subsequently got split along the Pranhita-Godavari rift zone into the Bastar and Dharwar cratons. The rift valley eventually developed into a sedimentary basin hosting the Proterozoic and Gondwana Group of sediments sequentially, apparently separating the two cratons on the map. (C) 2021 International Association for Gondwana Research. Published by Elsevier B.V. All rights reserved.

Formation of Archaean felsic continental crust in the western Dharwar Craton, India: Isotopic and trace element constraints from detrital zircons

The nature of the early terrestrial crust and how it evolved through time remains highly controversial. Whether conventional plate tectonics operated in the Hadean and early Archean and when it came into existence remains unclear. Here, we describe U-Pb ages, Hf isotope composition and trace element chemistry of 3.95–3.10 Ga old detrital zircons from the Singhbhum Craton in eastern India. The >3.7 Ga old zircons of this suite have crust-like Hf isotope compositions with strongly negative εHfi and their granitoid sources formed by intra-crustal reworking of a Hadean protolith that was extracted from primitive mantle at 4.4–4.5 Ga. The trace element and Hf isotope compositions of the zircons record a transition from higher Nb/Th (0.070 ± 0.010), Nb/U (0.045 ± 0.005), crust-like Hf isotope compositions, and longer crustal residence times of the protoliths prior to 3.7–3.6 Ga, to lower Nb/Th (0.032 ± 0.012), Nb/U (0.024 ± 0.009; 1σ), mantle-like Hf isotope compositions, and shorter protolith residence times post 3.7–3.6 Ga. The Nb/Th and Nb/U fractionation at 3.7 Ga seen in the detrital zircon record can be explained by transition to granitoid production at greater depths in an oceanic plateau-like regime. However, had that been the case, the crustal residence times of the protoliths of the granitoids from which the detrital zircons were sourced should have progressively increased with time, given the >1.1 billion years protracted history of granitoid magmatism in the craton, which is contrary to what is observed. We suggest that the changes in the granitoid chemistry recorded by the detrital zircons document a significant change in the depth of melting of the protoliths as well as in the tectonic setting of continental crust formation, and argue that it marks the transition to granitoid production from oceanic plateaus to arc-like tectonic environments. Broadly similar transitions at ca. 3.6 Ga have been documented in gneisses from the Acasta Gneiss Complex, the Jack Hills zircons and in detrital zircons from the Wyoming Province, which suggest that the end of the Eoarchean may have been marked by widespread transition in planetary tectonic regime.

The Thanewasna copper belt in Bastar Craton of central India is well-known for Cu +/- Au mineralization. In this study, we use major and trace element chemistry of magnetite, hematite, and pyrite, as well as the sulfur isotope composition of chalcopyrite, pyrite and barite from the deposit to characterize the mineralization and to constrain its petrogenesis. The mineralization is hosted in quartz-chlorite veins associated with 2.5 Ga and 1.6 Ga granitoids. The mineralization is focused along the NW-SE trending Thanewasna brittle-ductile shear zone and comprises disseminated and vein-hosted Cu-sulfides, mainly chalcopyrite and pyrite intergrown with minor magnetite, hematite, and sulfide-free barite. The associated hydrothermal alteration is characterized by pervasive potassic-sodic alteration and chloritization. Calcite and sulfide-bearing barite veins postdate the Fe-oxide and Cu-sulfide ores. At least two generations of magnetite, hematite, and pyrite were identified based on their textural and trace element characteristics. Texturally early magnetite (Mag-I) displays oxy-exsolution of ilmenite and is of magmatic origin, representing the pre-mineralization igneous assemblage of the host rocks. Texturally later magnetite (Mag-II) is of hydrothermal origin and replaces Mag-I. It has high Co and Mg concentrations and shows dissolution and re-precipitation texture as well as evidence for high-temperature annealing. Martitisation of Mag-I and II associated with chloritization and Cu-Au mineralization produced hematite. The delta S-34(VCDT) of syn-mineralization pyrite and chalcopyrite (-0.77 parts per thousand to -4.28 parts per thousand) is suggestive of magmatic sources for the sulfur. Post-mineralization barite veins have delta S-34(VCDT) between +10.31 parts per thousand and +17.55 parts per thousand which indicate that the sulfur was derived from seawater sulfate without going through an intermediate stage of reduction. Variation in the sulfur isotopic compositions of sulfide and sulfate was the result of dilution and cooling of the metalliferous fluid after interaction with meteoric fluids, which triggered the deposition of Cu +/- Au along structural weak planes. The widespread presence of iron-rich breccias, association with crustal-scale shear zone, pervasive K-Na alteration, chloritic and advanced argillic alteration, the involvement of magmatic and non-magmatic fluid and Cu-Fe-Au-Ag-Ba-REE metal association are all suggestive of IOCG-style mineralization at Thanewasna. This supported by the Ti, Al + Mn, Ti + V concentrations and Ti/V, Ni/Cr, Ni/(Cr + Mn) ratios of Mag-II and hematite. The Co/Ni ratios of pyrite further supports a hydrothermal origin of the deposit, unrelated to skarns or copper porphyry, having similarity with known IOCG deposits. The identification of IOCG-type deposits in the Thanewasna region gives a boost to deeper sub-surface exploration in this belt as well as in similar geological setting elsewhere.

The Western Dharwar Craton in southern India is underlain by Paleoarchean to Neoarchean granitoids. Here, we use major-trace element chemistry and zircon U-Pb-Hf isotopic composition to identify major components of the crust, constrain the timing of juvenile crust extr action, and discuss the implications for Archean tectonic processes. The granitoids are metaluminous to weakly peraluminous, magnesian, and calcic. They were derived from basaltic protoliths with minor components sourced from pre-existing felsic crust. Low La/Yb and Sr/Y indicate shallow garnet-free plagioclase-bearing amphibolitic sources. The granitoids display large variations in concentration of trace elements, attributed to plagioclase accumulation or fluid-assisted mobilization of REEs during metamorphism. Zircon ages help to constrain four major episodes of granitoid crust formation at 3.43-3.41 Ga, 3.36-3.34 Ga, 3.29-3.25 Ga, and 2.66-2.65 Ga. The 3.43-3.41 Ga, 3.36-3.34 Ga, and 3.29-3.25 Ga granitoid suites have positive epsilon(Hfi) (2.7-4.5) and plot on a common cm; vs. time trend consistent with repeated granitoid extraction at 3.43-3.41 Ga, 3.36-3.34 Ga, and 3.29-3.25 Ga from mafic sources that separated from model depleted mantle between 3.55 Ga and 3.35 Ga. The epsilon(Hfi) (0.4-0.69) of the 2.66-2.65 Ga Neoarchean granitoids can be explained by melting of similar 3.35 Ga mafic crust or by mixing between juvenile magmas and preexisting granitoids. Uranium-Pb ages from metamorphic zircons indicate polyphase metamorphism of the granitoids at 3353-3329 Ma, 3264-3256 Ma, 3187-3141 Ma, 3083-3062 Ma, and 2574-2526 Ma. Hf-isotopic data from zircons in granitoids from several cratons indicate that prior to c. 3.5 Ga most granitoids have chondritic or crust-like epsilon(Hfi) explained by repeated granitoid extraction from long-lived mafic crusts with limited interaction with juvenile magmas. Juvenile eta and short protolith residence times of the Western Dharwar Craton Paleoarchean granitoids is suggestive of a tectonic setting with rapid recycling of basalts as in subduction zones. In contrast, greater protolith residence times and crust-like signature of granitoids older than 3.5 Ga in the crustal record indicate a tectonic setting where basalts persisted for prolonged periods of times such as in an oceanic plateau.