This contribution presents a synthesis of tectonic fabrics, metamorphic, geochronologic, elemental and Nd-Hf isotope data addressing evolution of Archean crust through accretionary to collisional orogenesis in the Dharwar craton. A large crustal corridor was chosen across the Chitradurga boundary shear zone covering western and central blocks forming a wide time window into the Archean Earth.The western block preserves 3430-3150 Ma TTG-type granitoids with 3380-3150 Ma komatiite volcanics, 3000-2850 Ma Kibbanahalli arm and 2740-2677 Ma Chitradurga belt. P-T data reveal two thermal events with a 2960 Ma event [6-8 kbar/500-690°C] and a 2620 Ma high-pressure event with 12-13 kbar/350-450°C. Elemental characteristics of TTGs with Nd-Hf isotope [ƐNd(T) = +2.9 to -0.9; in-situ Hf (ƐHf(T) =+5.9 to 0.0)] reveal their origin by melting of newly formed mafic arc crust. The low to moderate incompatible elements coupled with Nd isotopes [ƐNd(T) = +2.7 to -1.0] of komatiites suggest their origin from heterogeneous deeper mantle. Higher incompatible element contents (total REE=28.27-158.41 ppm) and Nd isotopes [ƐNd(T) =-0.2 to -1.5] of Kibbanahalli arm volcanics suggest their derivation from primitive mantle. Collision of oceanic plateaus, arcs, granitoid crust caused crustal thickening, lower crustal melting causing generation of ca. 3000-2960 Ma potassic granites. Elemental and Nd isotope data [ƐNd(T) = +3.9 to - 4.1] of Chitradurga volcanics point depleted to primitive mantle source with crustal contamination. Elemental and Nd isotope [ƐNd(T) = +1.1 to -7.2] data of ca. 2600 Ma potassic granites are attributed to melting of thickened crust in a collisional setting.The central block comprises 2740 Ma Javagondanahalli greenstone belt, minor 3400-3100 Ma TTGs with widespread 2680-2600 Ma transitional TTGs and 2560-2500 Ma sanukitoids, 2500 Ma anatectic granites. The crust was affected by three metamorphic events during 3140 Ma, 2630 Ma and 2500 Ma. Elemental and Nd isotopes [ƐNd(T) = +2.6 to -0.4] of TTGs reveal their origin by melting of thickened arc crust. Incompatible elements and Nd isotope [ƐNd(T) = +0.1 to -2.3] data of Javagondanahalli volcanics attributed to their origin from depleted mantle with crustal contamination. The elemental and Nd isotope [ƐNd(T) = +2.0 to -1.6] of transitional TTGs argue for melting arc crust and mantle. The high incompatible elements contents with Nd isotope [ƐNd(T) = +1.7 to -2.6] signatures of sanukitoids suggest melting of enriched sub-arc mantle. The high SiO2, Nd isotope [ƐNd(T) = 0.1 to -7.3] of anatectic granites suggest reworking of thickened crust through collision of crustal blocks ca. 2560-2500 Ma.The geodynamic evolution of the Archean crust across the boundary shear zone involves a shift from plume to shallow subduction ca. 3400-3200 Ma and accretionary to collisional orogenesis during ca. 3000-2500 Ma. The rise of continent above sea level by 3000 Ma subjected to oxidative weathering supplied nutrients to oceans. Isotope biomarker data reveal transient surface environments involving anoxic to fluctuating redox conditions and microbial activity by Neoarchean. The microbial activity further enhanced biomass production and organic carbon burial, ultimately driving the surface oxygenation led to the building of habitable continent at the dawn of Great Oxygenation Event.

The Wangtu Gneissic Complex (WGC) is a Paleoproterozoic granite-gneiss complex located in the Wangtu-Karcham-Akpa section of the Sutlej Valley in the Himachal Himalaya, India. The basement of the WGC remains mostly in its original state. This article presents the geochronology of the granite gneisses, as well as a study of the thermal effects these rocks had on the neighbouring Wangtu metasediments. Dating of zircons by the ID-TIMS method in two granite-gneisses yields ages of 1872.1 ± 2.5 Ma and 1861 ± 13 Ma. The granite-gneisses exhibit similarities to porphyry-type granite, characterised by the presence of feldspar and quartz clasts, which are wrapped around by biotite and muscovite minerals. Monazite in two metasedimentary rocks of the WGC define U-Th-Pbtotal chemical ages of 1800 Ma but with partly more reset values down to 1400 Ma. Partial discordance of both zircon and monazite reflects the Cenozoic tectonics affecting the region. The results obtained from this study reveal the north Indian continental margin was an active subduction zone during the Paleoproterozoic Columbia supercontinent assembly that extends across the Himalaya.

Understanding when and how mobile-lid plate tectonics initiated on Earth is a fundamental question for understanding the evolution of early Earth. Here we integrate whole-rock geochemistry, phase-equilibria modelling, zircon U–Pb geochronology, zircon trace-element systematics, and in situ Hf isotope data from anatectic gneisses, magmatic charnockites, and tonalite–trondhjemite–granodiorite (TTG) gneisses in SW Bastar Craton, India. Zircon U–Pb ages define three discrete episodes at ∼3.65 Ga, 3.64–3.60 Ga, and 3.44–3.40 Ga for the emplacements of anatectic gneisses, syn-collisional magmatic charnockites yet recorded in the Indian landmass, and TTGs, respectively. Phase-equilibria modelling suggests the emplacements occurred at mid- to lower-crustal (∼30–50 km) depths, at ∼775 °C for anatectic gneiss, ∼950–1050 °C for charnockites, and ∼850–900 °C for TTGs. Trace-element patterns and zircon geochemical signatures are consistent with melt generation from subduction-modified mafic crust. Slightly positive to negative zircon εHf(t) values in anatectic gneisses and charnockites indicate magma generation involved interaction between juvenile melts and older Hadean–Eoarchean crust; on the other hand, TTGs yield predominantly negative εHf(t) values and older model ages, consistent with Hadean–Eoarchean crustal reworking. We integrate the field relation, phase-petrological, geochemical and geochronological data from the SW Bastar Craton to infer the nascent convergent tectonics on the Earth initiated in a 30–50 km-thick crust in the Eoarchean.

We present mineralogic and elemental data on the Banded Iron Formations (BIFs) from the volcano-sedimentary greenstone belts of the Western Dharwar Craton to address redox conditions of Archean Oceans and origin of BIFs. The studied BIFs are restricted to the uppermost stratigraphic levels in the Sargur Group and Dharwar Supergroup greenstone belts. The BIFs of the older Sargur greenstone sequence are characterized by thick chert layers, which are interspersed with thin Fe-oxide and silicate layers. Iron-rich amphibole grunerite indicates that BIFs from the Sargur Group underwent lower-amphibolite facies metamorphism. In contrast, oxide-silicate-carbonate-sulphide facies BIFs characterize younger Dharwar Supergroup greenstone belts. Rare silicate assemblages (e.g., stilpnomelane orreibeckite) in BIFs of Dharwar Supergroup reveal greenschist facies metamorphism. Field, mineralogic and elemental characteristics of studied samples show affinity to Algoma-type BIFs. The studied BIFs show significant variation in SiO2 (49.00-53.00 wt%) and Fe2O3 (27.00-51.5 wt%) content. The concentration of all other elements is typically <1 wt% except two samples of BIFs from the Chitradurga basin exhibit higher Al2O3 (5.42 wt%) and CaO (9.56 wt%) reflecting traces of terrigenous input. The low Sigma REE content (<20 ppm) of studied BIFs from the Sargur Group Holenasirpur, Dharwar Supergroup Bababudan, and Chitradurga - Dharwar-Shimoga greenstone belts preclude continent derived terrigenous input whilst higher total REE (30-53 ppm) of two BIFs samples from the Chitradurga basin is in agreement with traces of terrigenous input. BIFs from the older Sargur Group and the younger Dharwar Supergroup exhibit positive Eu anomalies pointing to BIFs sourced from hydrothermal plumbing system. The trace element ratios (Y/Ho, Sm/Yb, and Eu/Sm) consistent with a dominant hydrothermal input in their origin. The mineralogical facies changes, combined with the redox-sensitive elemental signatures coupled with published redox sensitive isotope biomarkers suggest fluctuation in the redox conditions of ocean basins through Archean and oxygenation of ocean initiated at least two hundred million years before the Great Oxidation Event (GOE).

This article presents the findings of a petro-chronological investigation on two-pyroxene mafic rocks (orthopyroxene - clinopyroxene > plagioclase > quartz > biotite) found as enclaves within 2500 Ma aged magmatic charnockites in the East Dharwar Craton (EDC). The Mg number (100MgO/(MgO+FeO)) of the analysed samples range between 42 and 57. The orthopyroxene-clinopyroxene and orthopyroxene-biotite associations are stabilized at around 1000-1050 degrees C, 0.7-0.8 GPa and 650 degrees C, 0.6-0.7 GPa, respectively. Chemically zoned monazites within pyroxene and plagioclase exhibit U-Th-Pb total age clusters that span 2638 Ma in the core, 2539 Ma in the rim surrounding the core, and 2458 Ma in the outermost part of the monazite grains. The zircon grains yield an upper intercept age of 2506 +/- 13 Ma. The geochemical results, pressure- temperature and geochronological data suggest the existence of Nb-rich, Ti-depleted mafic rocks in the EDC proto crust at similar to 2600 Ma, causing Neoarchean UHT metamorphism. Monazite formation at 2536 Ma was associated with the intrusion of charnockites in the EDC, resulting from the amalgamation of several crustal blocks. The < 2500 Ma monazite forms during isothermal cooling. The oldest (2638 Ma) tectonic episodes overlap with the timing of crustal growth and stabilization of the Kenorland supercontinent. [GRAPHICS] .

The BIFs in Bundelkhand Craton occurred as a discontinuous unit within the east-west trending Bundelkhand Tectonic Zone (BTZ). The BIFs were associated with amphibolite, calcsilicate rocks, and quartzite. The BIFs were massif in appearance in the Mauranipur (east of Bundelkhand Tectonic Zone, BTZ) that graded to layered variety in the Babina area (west of the BTZ). The Bundelkhand BIFs were characterized by 45 to 55 wt.% SiO2 and 44 to 55 wt.% Fe2O3 content. The Al2O3 content was usually low and varied between > 1 to 3 wt%. Barring a few samples, the MnO and CaO contents are < 1 wt.%. The higher MnO (~ 3.70 wt.%) and CaO (~ 1 wt.%) implied a different redox condition and involvement of CaCO3 in the early stages of BIF formations. The ΣREE content of Bundelkhand BIFs varied between 10 – 38 ppm, with Eu/Eu*SN values between 1.1 to 1.5. Geochemically, the BIFs were classified as Algoma-type BIFs deposited by low-temperature hydrothermal fluids. Monoclinic amphiboles, quartz and garnet were the dominant silicate phase for Mauranipur BIFs. Hornblende was present with monoclinic amphibole in the garnet-absent BIFs. Isolated grains of magnetite were dispersed throughout the Mauranipur BIFs. In contrast, alternate hematite and SiO2-rich layers with locally developed low-T amphiboles characterized Babina BIFs. The Fe-rich oxides were mostly hematite. Mineral microstructure and P-T pseudo-section modeling implied Minnesotaite and Fe-Ca carbonate phases were the primary minerals in BIFs, deposited at temperature ~ 200°C at 0.05 to 0.1 GPa. The primary minerals experienced dehydration and decarbonization reactions, leading to the stabilization of amphibole and garnet at a temperature of ~450°C and pressure of 0.1—0.2 GPa. When plotted in a P-T diagram, the increase in temperature corresponds to tectonic activity and plutonism, leading to micro-bock accretion and growth of Bundelkhand Craton.

The interplay of geological, chemical and biological processes that drive the oxygenation of the oceans-atmosphere of the early earth are spatially linked to the emergence of biosphere. Banded Iron Formations (BIFs) from the Archean greenstone belts form important archives for understanding the redox conditions of Archean surface environments. The Archean Dharwar craton preserves BIFs in the volcano-sedimentary greenstone belts of two distinct stratigraphic units (older Sargur Group and younger Dharwar Supergroup) corresponding to a time span of 3300-2600 Ma. These BIFs are confined to the highest stratigraphic levels forming summits of greenstone belts. They show alternate layers of chert and iron oxides, and petrographic data reveal diverse mineralogy including oxides, carbonate, sulphide and silicate facies. The occurrence of riebeckite and stilpnomelane in BIFs of younger Dharwar Supergroup indicates recrystallization under low-grade metamorphism. Slightly higher abundances of CaO and Al2O3 reveal significant influence of crustal source and precipitation of CaCO3 during BIFs formation. Mesoscopic layers of chert and iron oxide with variable thickness suggest fluctuating redox state of surface environments. The higher enrichment of Ni (6-26 ppm) than the Cr content (3-19 ppm) with variable Sr concentrations may be attributed to feldspar breakdown during hydrothermal fluid acceleration. Trace element ratios (Y/Ho, Sm/Yb, Eu/Sm) coupled with positive Eu anomalies of the BIFs from both older Sargur Group and younger Dharwar Supergroup BIFs reveal dominant hydrothermal input in BIFs origin. The PAAS normalized REE data preclude major continental input in the origin of BIFs. The variable negative Ce anomalies imply periodic fluctuating surface environments (oxic to anoxic) at the dawn of the Great Oxidation Event close to 2340 Ma. This is consistent with the published Fe, N, and S isotope data on the BIFs of the Western Dharwar craton.

The Singhbhum, Bastar, and Dharwar cratons in the South India Block (SIB) form a continuous mass of >2.5 Ga crystalline rocks in South India. In this contribution, we investigate whether these cratons grew together with the suggested ‘Ur’ framework or if they evolved separately. The Karimnagar granulite belt on the NE edge of the Eastern Dharwar Craton (EDC) contain enclaves of mafic granulites and high-Al metapelites within variably deformed charnockites and blastoporphyritic granitoids. The foliated charnockites exhibit magmatic flow texture, euhedral-subhedral pyroxene phenocrysts, and chess-board twinning in the quartz grains. Feldspar and pyroxene phenocryst laths share high-energy boundaries with quartz and each other. The Al-in-Opx thermometry indicates charnockites emplaced at a temperature > 900 °C. Also, the charnockites' whole rock chemistry supports an arc origin. The charnockites' oscillatory-zoned magmatic cores survive the recrystallization of zircon grains. The U-Pb Concordia plot shows a concordant age of 2680±15 Ma and 2504±12 Ma, from magmatic zircon cores. Recrystallized zircon grains exhibit an upper intercept age between 2510±4 Ma and 2509±3 Ma, overlapping with the U-Th-Pb ages in monazites (2502 -2508 Ma). The 207Pb/206Pb age versus εHf(t) plot of zircons indicates that ~2.5 Ga magmatic charnockites originated from

This study reports phase relations and U – Th – Pbtotalin-situ monazite geochronology of two-pyroxene granulite and high iron oxide bearing garnet-orthopyroxene granulite from the Karimnagar Granulite Belt, Eastern Dharwar Craton, India. The two-pyroxene granulite samples with granoblastic texture are composed of quartz, plagioclase, orthopyroxene, and clinopyroxene as major mineral phases, and biotite, zircon, ilmenite, and monazite occur as accessory phases. Small anhedral coronal orthopyroxenes surround the clinopyroxene megacryst and inclusions of clinopyroxene occur in orthopyroxene. Locally, biotites overgrow orthopyroxene and clinopyroxene along their rims. Garnet-orthopyroxene granulites are composed of orthopyroxene, garnet, spinel, quartz, plagioclase feldspar, hematite-magnetite, and ilmenite. Small, rounded orthopyroxene inclusions in garnet and anhedral coronal garnets surrounding orthopyroxene were observed. Spinels are hercynitic in composition. Ilmenite and tiny grains of spinel (~30 μm) occur as exsolve phases in magnetite. Magnetite separates spinel from garnet and orthopyroxene. The following metamorphic reactions can be proposed from the mineral assemblage:Cpx megacryst + Pl = metamorphic Opx + Cpx (Two-pyroxene granulite) (a) Opx ± Ilm + Pl → Coronal Grt + Qtz, (b) Al-rich magnetite→ Magnetite + Spinel (Hercynite), Ti-rich magnetite → Magnetite+ Ilmenite (High iron oxide garnet-orthopyroxene granulite). The result from petrography, phase equilibria, and thermometry of the two-pyroxene granulite predicts that metamorphic orthopyroxene becomes stable at 0.65 Gpa - 950oC along a cooling path, and biotites overgrow orthopyroxene at 650 oC (0.65 GPa). Similarly, the result from grt-opx granulite implies a cooling path where coronal garnet becomes stable at 800 oC-0.65 Gpa.The U-Th-Pb analysis of monazite grains in pyroxene (38 analysis) and feldspar (25 analysis) from two-pyroxene granulite shows the oldest and youngest peak at 2635 ± 90 Ma and 2449 ± 44 Ma, respectively. The monazite in pyroxene (46 analysis) and quartz (14 analysis) from garnet-orthopyroxene granulite exhibits the oldest peak at 2449 ± 14 Ma and a tiny youngest peak at 1987 ± 29 Ma. Another sample of garnet-orthopyroxene (40 analyses) displays the oldest and youngest peaks at 2574 ± 32 Ma and 2448 ± 25 Ma, respectively.The late Neoarchean peak at ~2600 Ma retrieved from the pyroxene granulite and high iron oxide bearing garnet-orthopyroxene granulite is probably the protolith emplacement age of granulite, correlated with the accretion of Eastern Dharwar Craton and Bastar Craton as a part of extended Ur assembly. The early Paleoproterozoic peak at ~2450 Ma implies the formation of coronal garnet and metamorphic orthopyroxene during a cooling path.

In the Indian peninsula, the Singhbhum, Bastar, and Dharwar cratons in the South India Block (SIB) constitute a contiguous mass of >2.5 Ga crystalline rocks. Did the cratons develop as a coherently evolved mass since their origin, or do these cratons constitute an assembly of disparately evolved cratons? Variably-deformed charnockites in the Karimnagar granulite belt and associated blastoporphyritic granitoids at the NE fringe of the Eastern Dharwar Craton (EDC) contain enclaves of mafic granulites, high-Al metapelites and anatectic quartzofeldspathic gneisses. The charnockites are demonstrably intrusive into the enclave suite. The enclave suite exhibits steeply-plunging reclined folds; the axial planes of the folds coincide with the N-striking tectonic fabrics in the Karimnagar charnockite/granitoids. The foliated charnockites display magmatic flow texture defined by trains of euhedral alkali feldspar, contain euhedral-subhedral pyroxene phenocrysts, and the quartz grains exhibit abundant chessboard microstructure. The weakly-strained euhedral laths of feldspars and pyroxenes phenocrysts share high-energy boundaries between themselves, and with quartz. Emplacement temperatures of the magmatic charnockites at similar to 900 degrees C are obtained from Al-in-Opx thermometry. Whole rock chemistry is consistent with an arc-related origin for most charnockites. In zircons within charnockites, variably zoned cores yield ages of 2680 +/- 15 Ma and 2504 +/- 12 Ma in the UPb Concordia plot. Recrystallized domains in zircon grains yielded upper intercept ages constrained between 2510 +/- 4 Ma and 2509 +/- 3 Ma, identical with the U-Th-Pb chemical ages (2502-2508 Ma) retrieved from monazites. The zircon epsilon Hf(t) values (- 4.85 to 1.31) suggest the similar to 2.5 Ga magmatic charnockites were derived from <3.0 Ga crustal sources. The late Neoarchean magmatic charnockites in the EDC margin were emplaced in a 2.7-2.5 Ga convergent tectonic setting, and the high-T magmatic charnockites formed due to delamination of a subducting (E-W shortening) oceanic crust. The subduction possibly relates to the late Neoarchean growth of the Dharwar craton involving the assembly of disparately-evolved crustal blocks, now parts of the Dharwar craton. The findings suggest that the emplacement of Karimnagar magmatic charnockites in a contractional setting is unrelated to an accretion between the Eastern Dharwar and the Bastar cratons, as suggested by earlier workers.

This paper reports new mineralogical and geochemical information on the Neoproterozoic Koraput Anorthosite pluton in domain-2 of the Eastern Ghats Mobile Belt. The lenticular-shaped, NE-SW trending small Koraput Anorthosite Pluton is dominated by gabbro-anorthosite, anorthosite sensu-stricto, and norite-diorite. Isolated patches of ferrodiorite (residual melt following crystallization of anorthosite) occur at the pluton margin. The estimated magmatic P-T conditions for anorthosite emplacement are similar to 1000 degrees C and similar to 1.1GPa. In addition, the intermediate Anorthite (48-52 mole %) presence in plagioclase of gabbro-anorthosite and anorthosite indicates plagioclase crystallisation and accumulation at 30-40 km (circa 1 GPa) depth near the crust-mantle boundary. Furthermore, the geochemical traces suggest Koraput anorthosite pluton crystallized from a less fractionated basaltic magma. The REE and trace element systematics of anorthosite and norite-diorite exhibit enriched LILEs over depleted HFSE with negative Nb, Ta, Th, and Zr anomalies. Gabbro-anorthosite and ferrodiorite, on the other hand, exhibit positive Nb, Ti, and negative Zr and Th anomalies. Nb/Th versus Nb/La diagram implies lithodemic units in Koraput Anorthosite pluton are variably contaminated by crustal sources. Integration of geochemical data with available monazite age suggests that the Koraput anorthosite pluton in isotopic domain-2 of the Eastern Ghats Mobile Belt was emplaced during the collision between proto-India and Antarctica during the Rodinia assembly.

As a tectonic window into the Lesser Himachal Himalaya, India, a group of metasediments and gneissic rocks, known as the Jutogh Group and Wangtu Gneissic Complex (WGC), occurs near the Jhakri thrust to the west and Wangtu to the east. In the Jutogh Group, chlorite-mica schist, garnet-staurolite schist and sillimanite-schist develop successively. The formation of chemically zoned garnet, which destabilized low-temperature assemblages, is predicted to be at 550–650 °C and 0.8–0.9 GPa by phase equilibria modelling. The retrograde segment consists of exhumation and cooling, yielding a tight clockwise P–T path. Moreover, textural observations and in-situ U-Th-Pb chemical dating indicate that metasedimentary rocks contain Cambrian monazites. These monazites have ages that cluster around 500 Ma. The ƐNd[1.8Ga] of Jutogh rocks ranges from − 1.0 to -8.1, with depleted mantle-model ages between 3.07 and 2.25 Ga. The garnet core and its leachates yield an Sm-Nd isochron age of 472 Ma. Another Sm-Nd isochron age of 454 Ma is obtained from biotite, garnet rim, and garnet rim leachate. According to phase equilibrium modelling, Sm-Nd dating, and monazite geochronology, the Jutogh Group experienced metamorphism along the northeast margin of Gondwana during the Cambro-Ordovician accretion.

The paper presents novel geochemical and geochronological data from granites in Khammam, Eastern Dharwar Craton (EDC), India. The studied granites contain major mineral phases like quartz, alkali-feldspar, plagioclase, biotite, and muscovite in decreasing order of abundance. The accessory phases are epidote, titanite, and zircon. The samples comprise 70 --77 wt% SiO2 and 12-15 wt% Al2O3. The K2O and Na2O concentrations range from 2.57 to 5.65 wt% and 1.17 to 2.69 wt%, respectively. They are enriched in Rb, Th, and Pb and depleted in Nb, Ta, and Ti. On a chondrite-normalized plot, the samples exhibit a rightward trend with a negative Eu anomaly. Zircon saturation in silicate melts yields a temperature (TZr) of 859 - 978 degrees C. The microstructure and U - Pb isotopic analysis of zircon grains (n = 79) reveals the presence of magmatic and polymetamorphic grains with 207Pb/206Pb age clusters at 1844 Ma (number of analyses, n = 7) - 1858 Ma (n = 8), 1737 Ma (n = 5) -1768 Ma (n = 4), 1619 Ma (n = 7) - 1634 Ma (n = 6), and 1554 Ma (n = 5), respectively. The magmatic zircons exhibit epsilon(Hf) values between 3 and 18.9 with a two-stage model age of 2.03 Ga. In contrast, the metamorphic zircons exhibit epsilon(Hf) values between -5.6 and 18, yielding a two-stage model age of 1.97 Ga. The geochemical and geochronological studies indicate that the rocks are A2-type granite emplaced during the accretion of the eastern block of the North China Craton (NCC) and EDC between 1844 Ma and 1858 Ma. The zircons from 1737-1768 Ma and 1620 Ma show the time of metamorphic growth during Antarctica-Nellore Schist Belt (EDC) accretion. Finally, the U-Pb zircon ages from 1554 Ma represent Nuna's final amalgamation. The results of this study posit an association between EDC and NCC during Nuna assembly.

The North Indian Block comprises two important Archean nuclei, the Aravalli and Bundelkhand cratons. The existence of early Paleoarchean crust (3.59–3.54 Ga) in both nuclei is supported by zircon xenocrysts in 3.44–2.55 Ga tonalite-trondhjemite-granodiorite (TTG) gneisses, although the oldest rock records in the Aravalli and Bundelkhand cratons are represented by scarce exposures of ca. 3.31 and 3.55 Ga TTGs, respectively. The Archean crust in these cratons is largely composed of 2.58–2.50 Ga K-rich granitoids and sanukitoids. A synthesis of literature published during the last four years on these north Indian cratonic blocks revealed several new and important findings, which enabled us to improve our understanding of the evolution of the Archean crust. Integrated microstructure, petrological, geochemical, and latest phase equilibrium modelling and isotopic data have not only provided robust evidence for the Archean antiquity of the central Aravalli-Banded Gneissic Complex but also revealed many aspects of the metamorphic evolution of this terrane. For the Bundelkhand Craton, these data show craton-wide exhumation from 2.4 to 2.3 Ga, two discrete phases of Neoarchean TTG magmatism (ca. 2.71 and 2.68 Ga), deposition of the banded iron formations between 3.44 and 2.80 Ga and their peak metamorphism at ca. 2.5 Ga. The data also provide a better understanding of the anatomy of the intraterrane shear zones and the Paleo– to Mesoarchean supracrustal metavolcanics and metapelites.

This communication reports the results of geochemical investigations and detrital zircon geochronology of metasediments of the Khammam Schist Belt that occur at the trijunction of the Eastern Dharwar Craton–Bastar Craton–Eastern Ghats Belt. Biotite (XMg = 0.46–0.52) and muscovite (Si atom per formula unit (apfu) of 11 O = 3.08–3.17) with alkali-feldspar constitute the mineralogy of studied samples. The Ti content in biotite yields a mean temperature of 652 °C (1σ = 10 °C), and biotite–muscovite pairs yield an average pressure of 0.46 GPa (1σ = 0.06 GPa). Fe-Ti oxides and zircon occur as accessory phases. The Al2O3 exhibits a positive correlation with K2O and TiO2, which implies that mica and biotite control the major element abundances of studied samples. These samples indicate negative Sr and positive Th anomalies in a Post Archean Australian Shale (PASS) normalised spider diagram. Also, these samples show a nearly horizontal trend with (La/Yb) PASS varying between 0.56 and 1.92 with a negative to slightly positive Eu anomaly (Eu/Eu* = 1.20, 1σ = 0.38). LA-ICPMS analysis of detrital zircon grains (number of analyses = 100 from two samples) yields 207Pb/206Pb ages range from 1500 to 2600 Ma. The zircons grains with weighted average ages between 2500 Ma, 2400 Ma, 2200 Ma, 2000 Ma, 1900 and 1800 Ma exhibit magmatic and high-temperature deformation features. The 1604 Ma old zircons exhibit homogeneous domains and overgrowths over older zircons, implying metamorphic origin. The Chemical Index of Alteration (CIA = 66 to 77), Chemical Index of Weathering (CIW = 73 to 95), and Plagioclase Index of Alteration (PIA = 81 to 91) values indicate moderate to intense weathering of the source area. Source and tectonic discrimination plots imply a felsic source and active tectonic setting. Accordingly, 1900–1800 Ma old magmatic zircons in the current samples constrain the maximum depositional age for the Khammam Schist Belt. Compared with the detrital zircon geochronology of the North China Craton and East Antarctica, the current samples exhibit peaks at circa 2500 Ma, 2400 Ma, 2200 Ma, 2000 Ma, 1900–1800 Ma, and 1600 Ma, implying Khammam Schist Belt as part of the South India Cratonic Block shares similar geological history with North China Craton and East Antarctica. Our study suggests that North China Craton and East Antarctica were connected with the South Indian Cratonic Block during the Columbia assembly.

This paper reports the results of the geochemical study of the Jutogh metasedimentary rocks that occur as a tectonic window between the Lesser and the Higher Himalaya. The Jutogh Group of rocks are mostly mica-schists of different metamorphic grade. The weathering intensity parameters, such as chemical index of alteration (CIA), plagioclase index of alteration (PIA), and index of compositional variability (ICV), range from 81 to 65 (mean = 72), 97 to 68 (mean = 84), and 1.9 to 0.6 (mean = 1.2), respectively indicating low to moderate degrees of weathering. Transition element ratios [Ni/Co (6.98 to 2.88), and V/Ni (2.32 to 1.27)], and major and trace element geochemistry imply recycled, felsic to intermediate, Archean to post-Archean are the sources for Jutogh rocks. The tectonic discrimination diagram implies an active continental margin setting for the deposition of the Jutogh metasediments. The geochemical data from the Jutogh rocks, when combined with the S-type Paleoproterozoic granite magmatism, imply the existence of an active tectonic setting during the deposition of the Jutogh sediments at the northern margin of the Indian continent during Nuna assembly.

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

In this article, novel geochronological (U–Pb SHRIMP) and geochemical data are presented from the lowermost sandstone unit (Par formation), basement granites of Gwalior Basin and sandstones from the Bhopal Basin, located along margins of the Archaean Bundelkhand Craton. The geochemical variation diagrams imply that sandstone units in the Gwalior and Bhopal Basins were deposited in rift-induced passive margin tectonic settings. In contrast to the magmatic features that are preserved in the zircons of granite of the Gwalior Basins, detrital zircons from sandstones of both basins are fragmentary and polymodal in size. The magmatic zircon grains from the basement granites yield a 207Pb/206Pb concordant age of 2538 ± 2 Ma. A group of detrital zircons from the sandstone of the Gwalior Basin with concentric magmatic zonation yield a weighted mean average age of 2564 ± 24 Ma. The detrital zircons from Gwalior Basin exhibit a patchy U-Th distribution overgrowing the magmatic zonation yield average age of 2044 ± 2 Ma. The detrital zircons from the Bhopal basin yield three distinct concordant ages of 2511 ± 5, 1694 ± 6, and 1355±9 Ma. The presence of ~2540 Ma concordant zircon population with concentric zonation in the sandstone of Bhopal Basin suggests their derivation from the granite of similar age. Therefore, an extension of Bundelkhand Craton granite below the Bhopal Basin is suggested. The 2500 Ma ages from the Gwalior granites are linked to global magmatic activity leading to the stabilization of extended Ur at ~2500 Ma. The 2048 and 1355 Ma ages from the Gwalior and Bhopal Basins, respectively, are concluded as the maximum depositional age (MDA) of the lowermost stratigraphic units within the basins. The MDAs are concluded to be the timings of passive margin basin formations along margins of the Bundelkhand Craton during extended Ur and Nuna or Columbia disintegration, respectively, during plume-driven tectonics.