Singhbhum Craton Research Articles

Petrogenesis of Neoarchean (2.80–2.75 Ga) Jagannathpur volcanics and the Ghatgaon and Keshargaria dyke swarms, Singhbhum craton, eastern India: Geochemical, Sr[sbnd]Nd isotopic and Sm[sbnd]Nd geochronologic constraints for interaction of enriched-DMM derived magma with metasomatised subcontinental lithospheric mantle

Petrogenesis of Neoarchean dyke swarms and dispersed volcanic successions in the Singhbhum craton can potentially constrain mantle heterogeneity. Their arc-like trace element contents, that have a mismatch with their intracratonic extensional setting, were interpreted to propose widely varied genesis from either an enriched mantle (EM I) or wholly from a metasomatised subcontinental lithospheric mantle (SCLM). In order to test the type of enriched source(s) of magma to the dykes swarms and volcanics, geochemical modeling, Sr and Nd isotopic analyses and geochronology were conducted. The Jagannathpur amygdular volcanics, one such unmetamorphosed volcanic succession, yielded an SmNd isochron age of 2799 ± 67 Ma (2σ) with Ndi = 0.50895 ± 0.00006, MSWD = 0.36 (n = 16) and εNd(T) = −1.12 ± 0.50. As the eruptive age is indistinguishable within error to the Ghatgaon (2762.4 ± 2.0 Ma, 2752.0 ± 0.9 Ma) and the Keshargaria (2800.2 ± 0.7 Ma) dyke swarms, the dykes are interpreted as coeval feeder conduits to the volcanics. Enriched LILE and LREE, Nb/Th and Zr/Th ratios coupled with highly radiogenic present-day Sr isotopic ratios which have mantle-like 87Sr/86Sri ratios (0.7031–0.7055) and negative εNd(T) values (between −1.8 and − 5.6 for the dykes and − 1.3 and − 1.4 for the Jagannathpur volcanics) indicate that the source mantle components underwent enrichment processes likely by pre-2800 Ma subduction. The primitive mantle-normalized trace element patterns for these dykes and volcanics have pronounced negative Nb-Ta-Ti anomalies and their arc-like geochemistry suggest interaction with metasomatised SCLM. Generation of primitive magmas has been modeled by two end member components involving 18% partial melt from enriched-DMM (depleted MORB mantle) [100–70%] and interaction with low degree (5%) partial melt of metasomatised SCLM [0–30%]. These magmas ponded at Moho depths and underwent assimilation-fractional crystallization (AFC) forming the diverse dykes and basaltic andesitic-andesitic volcanics. We link the geophysically imaged Mid Lithospheric Discontinuity to depth of metasomatised SCLM beneath the Singhbhum craton that formed ≥2800 Ma ago.

A plume - mantle interaction model for the petrogenesis of komatiite - komatiitic basalt - basalt - basaltic andesite volcanism from the Paleoarchean (3.57–3.31 Ga) Iron Ore Group greenstone belts, Singhbhum craton, India: Constraints from trace element geochemistry and Sm[sbnd]Nd geochronology

The Paleoarchean Singhbhum craton greenstone belts comprise basalt, interbedded minor komatiite (both alumina depleted and undepleted, ADK and AUK, respectively), komatiitc basalt, dacite and chert grouped as (~3.57 Ga) southern Iron Ore Group (S-IOG, Daitari samples) and ~ 3.31 Ga eastern Iron Ore Group (E-IOG, Dabanki samples). Considering the importance of metabasalt in formation of TTG batholiths, modeling their petrogenesis from mantle sources and SmNd geochronology was conducted. The rocks resemble Archean non-arc greenstone basalt (Nb/Th = 3.61–10.3) with tholeiitic affinity. The ADK of S-IOG was modeled by 37% partial melting of garnet lherzolite, komatiitic basalt was derived from ADK magma by ~25% assimilation fractional crystallization (AFC) and ~ 16% AFC of this magma formed tholeiitic basalt. Derived from depleted parental magmas they yield an isochron age of 3573 ± 63 Ma (2SD), Ndi = 0.50810 ± 0.00008, MSWD = 0.59 (n = 10) and εNd (3573 Ma) = +2.03 ± 0.03. Dacite formation, modeled by mixing of melts between Eoarchean felsic crust and metabasalt, yielded an isochron age of 3507 ± 180 Ma (2SD), Ndi = 0.50800 ± 0.00015, MSWD = 0.15 (n = 11), εNd (3507 Ma) = −1.46 ± 1.71; ca. 3.8–3.9 Ga Nd TDM model ages indicate vestiges of Eoarchean crust. The AUK of E-IOG was modeled by ~45% partial melting and ADK by ~33% melting of garnet lherzolite mantle. About 32% AFC of primary ADK magma formed the komatiitic basalt that evolved to tholeiitc basalt magma (~24%) which on ~15% AFC evolved to basaltic andesite - andesite magma. Derived from depleted parental magmas, the E-IOG rocks yielded an isochron age of 3313 ± 110 Ma (2SD), Ndi = 0.50847 ± 0.00013, MSWD = 0.06 (n = 10), εNd (3313 Ma) = +2.62 ± 0.28. Petrogenesis of Paleoarchean greenstone non-arc basaltic volcanism and associated komatiite can be best explained by plume-mantle interaction and partial melting of ambient mantle followed by assimilation fractional crystallization of parental magmas, and does not preclude recycling of pre-existing crust.

A non-arc tectonic setting for the evolution of Archean gabbro anorthosite Complexes: Evidence from the Singhbhum Craton, eastern India

Understanding the petrogenetic evolution of Archean gabbroic cumulates provides a window to the mantle geodynamics operated in the early Earth. Gabbroic cumulates are associated with various tectonic settings including convergent plate boundaries, mantle plumes, mid-ocean ridges, anorogenic, post-orogenic, continental rift settings and oceanic plateaus. The exposures of preserved gabbroic suites in the Archean are limited. The Mesoarchean Mayurbhanj Gabbro Anorthosite Complex (GAC) is a well-preserved mafic body situated along the eastern margin of the craton along with concomitant anorogenic Mayurbhanj granite. These rocks are devoid of deformational structures and/or mineral recrystallization. Based on their mineralogical characteristics, GAC rocks are mainly grouped into gabbronorite, leucogabbronorite, leucogabbro and gabbro. The minimal abundance of magmatic amphibole and the variation in the anorthite content (An36-An84) rules out the role of a hydrous mantle source in the evolution of these rocks. The studied samples display tholeiitic trend transitioning to calc-alkaline field, major and trace element data indicates the fractional crystallization of olivine and pyroxene. The trace element systematics of the Mayurbhanj GAC show LILE enrichment over HFSE depletion, with negative Nb-Ta and mixed Zr-Hf and Ti anomalies. The geochemical signatures such as elevated Th/Yb, Nb/Yb, variable Dy/Yb and Dy/Dy* and varying Gd/YbCN ratios suggest that parental magmas of the Mayurbhanj GAC originated from a heterogeneous depleted mantle source. The studied rocks' Sr-Nd isotopic systematics reveal that their parental magma has undergone assimilation by a Paleoarchean felsic crust. We argue that the ‘arc-like’ geochemical signatures displayed by these rocks resulted from crustal contamination and may not be due to subduction origin. Consolidating the field, geochemical and isotopic evidence suggests that the Mesoarchean Mayurbhanj GAC possibly evolved from an anhydrous heterogeneous mantle source in a non-compressive tectonic regime.

Crust-mantle structure and lithospheric destruction of the oldest craton in the Indian shield

The Singhbhum craton is among the five Archean cratons of Peninsular India that preserves some of the oldest continental nuclei. In this work, we present a new and complete Bouguer gravity map of this craton with insights into its deep crust-mantle structure, lithospheric thickness and density variations beneath this craton. The conspicuous presence of high-order residual gravity low anomalies, together with low estimated densities, suggests voluminous presence of Singhbhum granitic batholiths that built the dominant crustal architecture. The isolated residual gravity highs correspond to the mafic and ultramafic volcanic suites like, Dhanjori, Simlipal and Dalma, while the relatively low gravity anomalies observed over the western volcanic suites like Malangtoli, Jagannathpur and Ongarbira, indicate their relatively felsic nature. The estimated lithospheric thickness of about ~ 130 km below the granitic batholithic region, and about 112 km beneath the Precambrian volcanic terranes, together with low effective elastic thickness (Te,) of only about 31 km, suggest a thin and weak lithosphere. The craton witnessed extensive lithospheric destruction with the removal of nearly 100–150 km of the cratonic root. The decratonization may be linked to subduction during the Paleo-Mesoproterozoic period, together with mantle plumes at different times, suggesting a combined mechanical, thermal and chemical erosion of the cratonic keel.

A Ca. 2.25 Ga mafic dyke swarm discovered in the Bastar craton, Central India: Implications for a widespread plume-generated large Igneous Province (LIP) in the Indian shield

A precise U–Pb baddeleyite age (2251 ± 4 Ma) has been obtained for an ENE-trending dyke exposed near the Chhura region of the Bastar craton, and additional dykes of similar trend are also reported from other parts of the northern Bastar craton such as in the Dongergarh and Pakhanjore areas. We propose a new widespread ENE-trending ca. 2.25 Ga Chhura mafic dyke swarm in the Bastar craton, which represents a continuation of the NE- to ENE-trending ca. 2.26 Ga Kaptipada swarm in the Singhbhum craton. The adjoining Dharwar craton also hosts ca. 2.26–2.25 Ga magmatism, the N- to NNE-trending Ippaguda-Dhiburahalli dyke swarm. A geochemical match between the ca. 2.25 Ga Chhura, the ca. 2.26–2.25 Ga Ippaguda-Dhiburahalli, and most samples of the ca. 2.26 Ga Kaptipada swarms corroborates a genetic link. Together these mafic dykes in Bastar, Singhbhum and Dharwar cratons, define the ca. 2.26–2.25 Ga Ippaguda (-Dhiburahalli-Chhura-Kaptipada) LIP. The relative post-2.25 Ga rotations between the three cratons would allow two alternative locations for the plume centre either at the eastern end of the Kaptipada swarm in the Singhbhum craton or at the south end of the Ippaguda-Dhiburahalli swarm in the Dharwar craton. Alternatively, convergence of the Churra, Kaptipada and Ippaguda-Dhiburahalli sub-swarms could suggest a plume centre location in the Godavari rift, between the Bastar and Dharwar cratons. Magmatic events of approximately this 2.26–2.25 Ga age are known from other parts of the globe including East Antarctica, and Kaapvaal and Zimbabwe cratons.

EPMA geochemistry and LA-ICPMS dating of allanite, epidote, monazite, florencite and titanite from the Jaduguda uranium deposit, Singhbhum Shear Zone, eastern India: Implications for REE mineralization vis-à-vis tectonothermal events in the Proterozoic Mobile Belt

The Singhbhum shear zone (SSZ), eastern India, located close to the boundary between the Proterozoic North Singhbhum Mobile Belt and the Archaean Singhbhum craton, is the best known uranium province and one of the most important copper districts in India. The uranium ores and associated rocks are enriched in rare earth elements (REEs). This study integrates texture, composition and in situ LA-ICPMS dating of allanite, epidote, monazite, florencite and titanite from the Jaduguda uranium deposit in the SSZ. The earliest LREE-rich allanite (Allanite-Ce) formed at 1883 ± 14 Ma and was subsequently replaced and overgrown respectively by LREE-depleted allanite and epidote at 1637 ± 11 Ma and 1107 ± 18 Ma. The earliest monazite (Monazite-Ce) formed at ca. 1809 ± 9 Ma, while a new generation of monazite and florencite are dated at 952.2 ± 7.9 Ma and 959 ± 83 Ma respectively. Titanite, discordant to the pervasive foliation, records ancient Pb-loss and probably new titanite growth at 978 ± 17 Ma.The SSZ witnessed protracted evolutionary history with accompanying multi-stages REE mineralization and mobilization, spanning over ca. 900 Ma. The Paleoproterozoic LREE-mineralization occurred in two different pulses at ca. 1.88 Ga and ca. 1.80 Ga predating the known ages of metamorphism. It is envisaged that extension-related faults developed at the present location of the SSZ acted as fluid conduits and localized the earliest ca. 1.88 Ga hydrothermal REE mineralization. It is unclear whether the ca 1.80 event is the continuation of the ca 1.88 Ga event or represents a separate and discrete pulse of mineralization in the same locale under different geotectonic environment. The ca. 1.64 Ga event associated with LREE-removal is related to either reactivation of the existing faults or partial closure of the mobile belt with concomitant shear deformation and metamorphism in the shear zone when the rocks in the northern mobile belt were thrust southwards along existing mineralized faults. The status of the ca. 1.11 Ga event is ambiguous. The 950 ± 50 Ma event, which primarily redistributed REEs from existing mineralization is related to the final closure of the mobile belt and reactivation of the SSZ associated with the formation of the greater Indian land mass in Peninsular India.

Geochemical Characteristics of Quartzite in Parts of Paleoproterozoic Dhanjori Group, Singhbhum Craton, Eastern India: Implications for Provenance and Paleoweathering

Abstract Singhbhum craton preserves the records of sedimentation, magmatism, and tectono-thermal events from Mesoarchaean to Neoproterozoic. The Dhanjori Group (DG), located on the northeast margin of the Singhbhum craton, comprises of a variety of rocks including quartz pebble conglomerate, quartzite, schist, interlayered with mafic to intermediate and rarely acidic lava flows, tuff and agglomerate. Petrography and geochemical characteristics of the Dhanjori quartzite have been undertaken to interpret paleoweathering and provenance characteristics. Studied quartzites are made up of abundant quartz, feldspar, mica, and lithic fragments. With the help of geochemical data, the studied quartzites are classified as quartz-arenites and sub-arkoses. In addition to the A-CN-K plot, various chemical indices such as the chemical index of weathering (CIW), chemical index of alteration (CIA), and plagioclase index of alteration (PIA) indicate moderate to intense chemical weathering of the provenance under semi-humid climatic conditions. Rare earth element (REE) chondrite normalized patterns of the studied samples illustrate enriched light rare earth elements (LREEs) (LaN/SmN = 3.11 – 6.19), depleted heavy rare earth elements (HREEs) (GdN/YbN = 0.35 – 3.12) and negative Eu anomaly (Eu/Eu* = 0.55 - 0.87, ~ 0.68). Such patterns are similar to that of the upper continental crust (UCC). In the discrimination function diagram, studied samples of the Dhanjori Group fall in quartzose sedimentary field. In addition, La/Sc vs. Th/Co and La-Th-Sc diagrams, various ratios like Th/Sc (~0.61), La/Sc (~4.42), Th/Co (~0.03), La/Co (~0.11), and Cr/Th (~141.62) imply a mixed provenance for the studied samples. Hence, it has been inferred that the meta-sediments and orthoamphibolites of the older metamorphic group, Singhbhum granitoid complex, as well as associated Archaean metavolcanic suites, would have acted as the probable source rocks for the studied Dhanjori quartzites.

3.51 Ga old felsic volcanic rocks and carbonaceous cherts from the Gorumahisani Greenstone Belt – Insights into the Palaeoarchaean record of the Singhbhum Craton, India

In the Singhbhum Craton of India, Palaeoarchaean greenstone sequences have so far been reported from the south of the craton. In this study, we report a precise 3510 ± 3 Ma U-Pb LA-ICP-MS zircon age from a well-preserved felsic volcaniclastic unit of the Gorumahisani Greenstone Belt (GGB) exposed in the north-eastern part of the craton. The volcano-sedimentary sequence of the GGB comprises a typical Palaeoarchaean greenstone succession of submarine ultramafic to felsic volcanic rocks intercalated with banded iron formation and abundant carbonaceous chert. Chert of the GGB comprises banded black-and-white chert, granular chert, laminated chert and massive black chert, in striking similarity to Palaeoarchaean greenstone successions in South Africa and Australia. Raman spectroscopy of carbonaceous matter yielded an average of ~460 °C as an estimate for the peak metamorphic temperature in the study area. The good preservation and only greenschist-facies metamorphic conditions make the GGB an interesting target for Early Earth studies.

Tectonic evolution of the Paleoarchean to Mesoarchean Badampahar-Gorumahisani belt, Singhbhum craton, India – Implications for coexisting arc and plume signatures in a granite-greenstone terrain

An association of tonalite-trondhjemite-granodiorite (TTG), other granitoids and greenstones constitute the Paleoarchean-Mesoarchean Singhbhum craton in India. The deformed and metamorphosed greenstone succession of Badampahar-Gorumahisani belt (BGB) in eastern Singhbhum consists of mafic–ultramafic volcanics, intercalated chemical sediments in the lower part and clastic sediments in the upper part. Geology, structure and geochemistry of BGB mafic volcanics, contemporaneous TTG and slightly younger intrusive granite have been integrated to constrain the tectonic setting of Paleoarchean felsic crust generation and coupled deformation of granite-greenstone. Subalkaline, low-K BGB metabasalts show distinct tholeiitic trend of differentiation from komatiitic basalt parent magma. BGB metabasalts with LILE enrichment, negative Nb anomaly, and Ti/V ratio in the range 10–20, are comparable to island arc tholeiites, though the associated komatiites and high-Mg basalts suggest plume related origin. Limited crustal contamination of a komatiitic basalt magma cannot be ruled out altogether. Singhbhum granite batholith with older tonalite-trondhjemite and younger granite-granodiorite plutons were derived from low- to high-K mafic source, together with some TTG reworking for younger granites. With low HREE, higher primordial mantle normalized La/Yb ratio, insignificant Eu anomaly, and coupled depletion of Y and enrichment of Sr, older strongly deformed plutons compare well with the Archean TTG suite. The younger intrusive granites show weak positive Eu anomaly (Eu/Eu* ~ 1.3–1.7) and strongly positive Y anomaly. Geochemical discrimination (e.g. Rb vs Y + Nb) suggests comparison with volcanic arc granites, which is also supported by enrichment of LILE (K, Rb and Ba) and LREE, and relative depletion of HREE and HFSE. However, structural geometry of BGB and adjoining granitoid plutons, association with komatiite, absence of typical signatures of derivation from subduction wedge, and heterogeneity of source for the BGB mafic volcanics, suggest Paleoarchean crustal accretion by mantle plume activity as well as local shallow subduction or subcretion under a transitional tectonic regime.

Internal Stratigraphy of the Mesoarchean Keonjhar Siliciclastics, Singhbhum Craton, Eastern India: Paleogeographic Implications.

Abstract In comparison to the greenstone belt volcano-sedimentary successions, mature arenite dominated sedimentary deposits are very rarely preserved in Paleo-Mesoarchean rock record. Such arenitic deposits may be important for the recognition of extensive development of continental freeboard and onset of Phanerozoic style plate tectonics. The Keonjhar siliciclastics are ~715-m thick mature arenite-dominated Mesoarchean succession that unconformably overlies Paleo-Mesoarchean granite-greenstone core of the Singhbhum craton. The succession is mapped on 1:50,000 scale, and is designated as the Keonjhar Quartzite. It is subdivided into conglomerate dominated lower unit as the Asurkhol Member and mature arenite dominated upper unit as the Kamalpur Member. A lensoid body of iron ore clast bearing conglomerate unconformably overlies the Keonjhar Quartzite, and is designated here as the Chamakpur Conglomerate. The succession is repeated by three westerly dipping reverse faults that have upthrown the deeper parts of the basinal transects against shallower parts. The Asurkhol Member represents subaerial part of a coastal alluvial fan. The Kamalpur Member represents shallow-shelf depositional setting. Detailed mapping and recognition of the fault slices led to the reconstruction of the paleogeographic setting. The present study also highlights the importance for the stratigraphic correlation of the Keonjhar Quartzite with underlying metabasics of Malangtaoli- Jagannathpur lava and the overlying western IOG succession. The internal stratigraphic classification proposed here is also significant from economic point of view with regard to the occurrences of uraniferous QPCs in the Asurkhol Member and detrital iron ore deposits in the Chamakpur Conglomerate.

Transition from alluvial to wave-tide-dominated Meso-Neoarchean shelf sedimentation in the Mankarchua Quartzite, Singhbhum craton, eastern India

The Mankarchua Quartzite is a 300 m thick arenite-dominated succession developed on the southwestern margin of the Singhbhum craton, eastern India. Detrital zircon dates available from the succession suggest the age of the youngest population at 2.9 Ga. The arenite dominant succession with very low degree of deformation or metamorphic overprint preserves the depositional primary sedimentary structures and petrography for reconstruction of depositional setting and tectonic setting with considerable clarity. We classified the Mankarchua Quartzite into three members, namely, in the ascending order, the Rajabasa Member, the Timi Member and the Gurusanga Member. Facies analysis on the succession identifies eleven sedimentary facies that can be related to basin margin alluvial fan, wave-/tide-dominated lower shoreface to shelf transitional environments. The entire succession represents a lower order transgressive sequence presumably controlled by tectono-eustatic base level rise and drowning of a continental shelf. Three members can be related to higher order cycles that are likely to have resulted from local scale basin margin tectonics. Paleocurrent patterns corroborate to the alluvial fan/braided stream and wave-/tide-dominated depositional settings. The succession records transition in a narrow interval from coarse-grained conglomerate-pebbly sandstone to sandstone-siltstone-mudstone dominated facies associations in a Meso-Neoarchean drowning shelf.

Shock Metamorphic Features in the Archean Simlipal Complex, Singhbhum Craton, Eastern India: Possible Remnant of a Large Impact Structure

ABSTRACT The Simlipal complex in eastern India is an elliptical structure with diameter of ca. 50 km coinciding with an elliptical region of high gravity. It overlies the Archaean basement of the Singhbhum craton and has a ring structure characterized by complex series of concentric ridges with inward dipping slopes. Quartz clasts in melt-breccias from the complex display diagnostic shock metamorphic features such as two to three sets of decorated and annealed planar deformation features (PDFs), spall and concussion micro-fractures, and the presence of coesite. They also preserve microstructures suggestive of crystallographically-controlled melting/amorphization along two or three planar directions, and within concussion micro-fractures. The inferred shock pressures in excess of 40–60 GPa are possible only during bolide impact. The Simlipal structure is possibly the remnant of a large complex impact crater having an original diameter of at least 50 km. Although zircons from an impact melt rock furnish a concordia age of 3107±14 Ma, in the absence of any unambiguous shock metamorphic effects in them, it is difficult to assign the age to the impact event. Therefore, the age of the impact is currently unconstrained.

Unravelling depositional setting, age and provenance of the Simlipal volcano-sedimentary complex, Singhbhum craton: Evidence for Hadean crust and Mesoarchean marginal marine sedimentation

The Singhbhum craton of eastern India preserves an extensive record of basin formation spanning the Paleoarchean to Neoarchean. Although spatially extensive and well exposed, the absolute age, depositional environment, and regional correlations of many of the purportedly Archean basins of this craton remain poorly resolved. We present a detailed lithostratigraphic analysis of siliciclastic strata in the (lower) Simlipal volcano-sedimentary succession and report the first detrital zircon U-Pb ages from this succession. The studied section is dominated by fine- to medium-grained, quartz-rich sandstones, which preserve herringbone stratification, tidal bundles, soft sediment deformation structures along with ubiquitous trough cross-stratification. Petrographic study confirms these sandstones as quartz arenites and reveal their high textural and mineralogical maturity. These features are consistent with deposition of the lower siliciclastic succession of the Simlipal volcano-sedimentary complex within a tidally-influenced marginal marine setting. The new detrital zircon data support a ~3.08 Ga maximum depositional age for the succession and reveal a provenance with age peaks at ca. 3.55–3.45 Ga, 3.38–3.24 Ga, and 3.10–3.08 Ga. These ages likely correspond to local basement sources including the Older Metamorphic Tonalite Gneisses, the Singhbhum Granitoid Complex, and the Mayurbhanj Granite Suite. Two detrital zircons from our dataset have concordant ages of ~4.02 Ga and ~4.03 Ga. They represent the first Hadean detrital zircons recovered from any Archean strata in the Singhbhum craton, documenting the involvement of Hadean crust in the early development of the craton. The detrital zircons show prominent Pb-loss at ~1.2–1.0 Ga that exemplifies the tectonothermal imprint of a late Mesoproterozoic to early Neoproterozoic orogeny (likely related to the assembly of Rodinia) on the Singhbhum craton. Our findings further support the interpretation that the lower siliciclastic strata in the Simlipal succession are the lateral facies equivalents of alluvial fan deposits at the base of the Dhanjori Formation, exposed to the north.

Magmatic and Tectonic Setting of Archean Granitoids in the Southeastern Singhbhum Craton, India: Developing constraints with major and trace element geochemistry and geochronology

The Singhbhum craton is one of five Archean nuclei comprising Peninsular India. It is a composite Archean block that includes the Older Metamorphic Group, the Older Metamorphic Tonalite Gneisses, the Singhbhum Granite, and the Iron Ore Group as its major units. The ages of these components range from ~3.5 to ~3.1 Ga, although overlapping ages and similar rock types confound their genetic relationships. Plutonic felsic rocks from the southeastern Singhbhum craton (BK1: a foliated tonalite, KP1: a non-foliated granite, and SG14: a non-foliated granite) yield U-Pb (zircon) ages of 3321 ± 2 Ma (BK1), 3301 ± 1 Ma (KP1), and 3261 ± 1 Ma (SG14) that coincide with a pulse of Singhbhum Granite emplacement at 3.27 to 3.33 Ga. REE patterns and tectonic discrimination diagrams based on major and trace element ratios suggest a subduction zone setting for these rocks. We report major and trace element data for and compare them to previous works in order to characterize the Archean felsic plutonic history of the craton.

Alluvial fan to shallow marine sedimentation record in the ~3.0 Ga Keonjhar Quartzite, Singhbhum Craton, India: An example of Phanerozoic style passive margin sedimentation from the Mesoarchean

The arenite-dominant Mesoarchean Keonjhar Quartzite (>700 m) succession unconformably overlies the granitoid-greenstone core of the Singhbhum craton in the north and west of the Keonjhar town in eastern India. The Keonjhar Quartzite is characterized by eleven lithofacies. The lower part of the succession represents proximal subaerial fan association dominated by cohesive and cohesionless mass-flow conglomerates deposited in a falling stage to lowstand systems tracts (FSST-LST). The channelized conglomerates are likely to be incised valley fills (IVF) from the FSST. The differentiated mass-flow deposits interbedded with tractional deposits such as trough cross-stratified sandstone with ubiquitous evidence of wave-reworking represent subaqueous delta front setting. The upper 3/4th of the succession is dominated by mature wavy bedded arenites and is arranged in aggradational stacking pattern representing TST to early stage of HST of a tectonically driven sea level rise cycle. The Keonjhar Quartzite is a rare example of well preserved record of stable siliclastic shelf development during the Mesoarchean time. The arenite-dominated Keonjhar Quartzite is comparable to only a few well studied examples of such Mesoarchean stable siliciclastic shelf sedimentation, for example, the arenite-dominated units of the Mozaan Group of the Pongola Supergroup and its correlatable Westrand and Centralrand Groups of the Witwatersrand Supergroup in the Kaapvaal craton. The presence of thick mature arenite and wave-tide reworking implies existence of Mesoarchean stable shelf depositional setting similar to the modern day passive continental margins at least in the Singhbhum and in the Kaapvaal cratons.

Detrital zircon evidence for change in geodynamic regime of continental crust formation 3.7–3.6 billion years ago

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.

Earthquake source dynamics and kinematics of the Eastern Indian Shield and adjoining regions

The Eastern Indian Shield (EIS) consists of two cratonic nuclei, namely Singhbhum craton and Chhotanagpur Granitic Gneissic terrain. This area contains several crisscross faults, lineaments, shear zones, numerous hot springs and three major rivers (e.g., Ganga, Brahmaputra and Damodar). The area is regionally covered by 7 seismic stations and jointly recorded 16 events from the study area, and less noisy waveforms of 4 events were used for focal mechanism analysis using the Cut and Paste method. The focal parameters of these 4 events were compiled with results of 8 events computed by different workers for the study area. To understand the detailed tectonics, focal mechanisms of 21 events for the Himalayan segment were taken from CMT Harvard catalog of duration 1976–2017. Spatial variations of operative stress fields for major tectonic domains were analyzed in the present study based on stress inversion of focal mechanism parameters. We observed strike-slip-dominated movements in the EIS, which changes partially into extension in the northeast part between the Ganga and Brahmaputra Rivers. Thrust-dominated movements evidenced by focal mechanisms and the pure compression in the western segment of the Himalaya in the north might be promoting shear movements in the EIS and adjoining regions. The pure strike-slip in the eastern segment of the Himalaya and its deeper level account for lateral shearing and eastward movements of different tectonic blocks. The normal faulting earthquakes in the northeast part might be indicating stretching in the basement because of convergence of Indian lithosphere beneath the Myanmar plate.

Combined self-potential, electrical resistivity tomography and induced polarisation for mapping of gold prospective zones over a part of Babaikundi-Birgaon Axis, North Singhbhum Mobile Belt, India

The Palaeo- to Meso-Proterozoic (1.0–2.4 Ga) North Singhbhum Mobile Belt (NSMB) is an assembly of multiphase folded, low- to medium-grade meta-sedimentary and meta-igneous rocks, lying within the north Singhbhum crustal province. The mobile belt is situated between the Archean Singhbhum craton in the south and the Meso/Neo-Proterozoic (0.9–1.7 Ga) Chotanagpur Gneissic Complex in the north. Gold mineralisation of moderate concentration is reported from different parts of NSMB along shear /fracture zones within the volcano-sedimentary and meta-sedimentary rocks sequence. The mineralisation is structurally controlled and is associated with higher order shear zones. Gold occurs in association with sulfides like pyrite, arsenopyrite, pyrrhotite, chalcopyrite, sphalerite, etc. This work attempts to map the auriferous shear/fracture zone along the Babaikundi-Birgaon axis (BBA), which lies within the NSMB. In the present study, combined geophysical approach comprising self-potential (SP), electrical resistivity tomography (ERT) and induced polarisation (IP) methods were used for mapping of subsurface gold prospects. SP data were collected along 7 profiles at 10 m station interval with approximate profile separation of 100 m. The anomalies of possible ore bodies were found at depth of about 18–25 m using Euler deconvolution of SP data. The ERT and IP data were collected along four profiles at 10 m electrode spacing with approximate profile separation of 100 m. The inverted resistivity sections indicate very low resistivity value in the depth range of ∼20 m inferring highly conducting, while relatively high chargeability are also observed at the depth range of ∼25 m. The possible existence of Babaikundi-Birgaon lineation and the occurrences of sulfide minerals in quartz reef associated with gold mineralisation were mapped based on the horizontal locations and extensions of negative anomaly in SP data, low resistivity in 2-dimensional (2D)-inverted resistivity section and high chargeability in 2D-inverted IP section. Previous studies based on electron probe micro-analyzer (EPMA) and scanning electron microscope (SEM) analysis over the study area substantiate our combined geophysical interpretations for the presence of gold prospective zones along the BBA. Highlights Integrated geophysical approach comprising SP, ERT and IP methods Delineation of BBA Mapping of subsurface gold prospects/ mineralisation Validation of results using borehole data, EPMA and SEM–SED analysis of rock samples (a) Map showing profiles AA/, BB/, CC/ and DD/across the Babaikundi-Birgaon Axis (BBA). (b) Upward continued (60 m) self-potential (SP) anomaly map showing possible extension of a part of BBA. Schematic resistivity (c) and chargeability (d) distribution models showing possible extension of a part of the BBA. (e) mineralised sample with sulfide hosted quartz reef in BBA. The possible existence of BBA and the occurrences of gold-bearing sulfide minerals in quartz reef are mapped based on the horizontal locations and extensions of negative SP, high conducting / low resistivity in electrical resistivity tomography (ERT) and high chargeability in Induced Polarization (IP). Note that profiles C-C/ and D-D/ are not parallel to each other; their field orientation is shown in Figure 1(c) and Figure 2.

Constraining paleoproterozoic (∼1.7 Ga) collisional orogenesis between the Eastern Dharwar and Bastar cratons: New Sm–Nd garnet isochron and Th–U-total Pb monazite chemical ages from the Bhopalpatnam orogen, central India

The timing of assembly into India by amalgamation of cratonic fragments, is controversial with estimates ranging from Tonian, earliest Mesoproterozoic to Neoarchean. All models have as the nucleus the South Indian Block of Dharwar, Bastar and Singhbhum cratons. Although the time of assembly of the Bastar and Singhbhum cratons is uncertain, the implication of a proposed 1891–1883 Ma-aged Large Igneous Province, straddling the Bastar and Eastern Dharwar cratons is that their amalgamation occurred by Paleoproterozic time (≥1.9 Ga ago) and is at variance with the ages reported from the Bhopalpatnam granulite belt between 1.7-1.6 Ga ago. To test whether this belt formed by convergent collisional tectonics along the margins of these two cratons, petrochronologic analysis was conducted on high-grade rocks of this belt using garnet Sm–Nd and texturally-controlled Th–U-total Pb monazite chronometry.The whole rock-garnet Sm–Nd isochron from garnet-clinopyroxene-amphibolite in migmatite (M1a-stage), yielded an isochron age of 1692±13Ma with Ndi of 0.51042±0.00006 (2σ, MSWD = 2.5 n = 4) whereas a whole rock-garnet Sm–Nd isochron from interlayered garnet-sillimanite-rutile metapelite (M1b-stage), yielded an isochron age of 1675±7 Ma with Ndi of 0.50997±0.00003 (2σ, MSWD = 1.9 n = 3) Monazite inclusions within garnet porphyroblasts in this metapelite have a weighted mean age of 1703±28 Ma (2σ, MSWD = 0.95, n = 8), within error of the age of monazite inclusions within matrix biotite at 1665±16 Ma (2σ, MSWD = 0.56, n = 17). Post M1b stage lower temperature hydration-retrogression events likely occurred by late Mesoproterozoic time. The metamorphism followed a clockwise P-T path (high-pressure amphibolite-facies stage M1a P ≥ 12 kbar at ∼750 °C, followed by M1b granulite-facies stage with T ≥ 850 °C at lower pressures), interpreted as a response to crustal thickening during Paleoproterozoic continental collision. We propose that the Bhopalpatnam orogen is the exhumed locus of the leading edge of the Archean Bastar craton that was thrust under the EDC craton.

Transition from shallow to steep foliation in the Early Neoproterozoic Gangpur accretionary orogen (Eastern India): Mechanics, significance of mid-crustal deformation, and case for subduction polarity reversal?

The ENE-trending Gangpur Schist Belt (GSB) comprising foreland sediments and distended screens of mafic/ultramafic rocks is sandwiched between the Meso/Neoarchean Singhbhum Craton (SC) in the south, and the Early Neoproterozoic granitoids of the Chottanagpur Gneiss Complex (CGC). These meta-sediments are thrust (D2 deformation) northward along a shallow-dipping decollement in the CGC granitoids. The shallow foliations with orogen-parallel stretching lineation in granitoids are coaxial with axes of D2 recumbent folds in the meta-sediments; locally-developed orogen-normal extensional shears and en echelon quartz vein are associated with this deformation phase. The shallow-D2 structures are dissected by two orogen-parallel south-dipping shear zones (D3) with steep stretching lineations. Sinistral-normal kinematics dominates the shear zones, but the northern margins of the shear zones exhibit dextral and north-down kinematics. Analyses of NCKFMASH P-T pseudosections constructed for the meta-sediments suggest the pre/post-D2 stage was characterized by mid-crustal amphibolite facies near-isothermal loading punctuated by prograde heating. Th-U-Pb (total) ages of metamorphic monazite grains in the schists (1080–940 Ma) and the magmato-metamorphic ages of CGC granitoids (1020–940 Ma from previous studies) overlap with each other, but monazite (>1050 Ma) inclusion trails in the core of pre-S2 garnets predate the magmato-metamorphic ages in the granitoids.The D2 Early Neoproterozoic deformation in the GSB involved top-to-the-north translation of the foreland sediments along a mid-crustal decollement in the CGC, followed by transpressional deformation that caused inclined extrusion and lateral escape along orogen-parallel hinterland vergent shear zones. However, the initiation of SC-CGC accretion (>1050 Ma) possibly involved northward subduction (pre-D2 near isothermal loading) of the GSB foreland sediments that ultimately was linked to the emplacement of granitoids in the over-riding CGC plate. Cessation of the subduction and continued N-S shortening caused CGC to evolve as the overridden basement.