Eastern Ghats Mobile Belt Research Articles

Delineating the Lithotectonic Domains in the Eastern Ghats Mobile Belt: Implication for the Regional Exploration of the Metasediment Hosted Graphite and Manganese Ore Horizons

ABSTRACT The present work documents and discusses the spatial disposition and lithotectonic control of graphite and manganese mineralization associated with metasediments of the Proterozoic Eastern Ghats Mobile Belt (EGMB) of eastern Indian shield and attempts to evolve a working model for furthering their exploration activities. Detailed satellite image based trendline mapping was done for the part of EGMB north of the Godavari Rift to map the marker horizons and demarcate structural discontinuities. Based on the contiguity of mineralised zones and their disruption due to structural discontinuities in EGMB, a lithotectonic map has been prepared. Five lithotectonic domains having distinct disposition patterns of mineralisation have been made which are (i) the southernmost, Vizianagaram - Rajahmahendravaram Domain bounded on its east by the N-S trending Nagavalli Shear Zone (NSZ), (ii) the Nagavalli - Vamsadhara Domain lying between NSZ and Vamsadhara Shear Zone (VSZ), (iii) the central Daspalla - Phulbani Domain bounded by VSZ in the south and the Mahanadi Shear Zone (MSZ) in the north, (iv) the northernmost Angul - Redhakhol Domain located north of the MSZ and (v) the western Balangir Domain between the eastern margin of the Bastar Craton and the Tel Shear Zone (TSZ). The disposition of the mineralised zones is unique in each domain, primarily controlled by the second and third generation folding often modified by high strain zones. Based on this, a working model for exploration in brownfield and greenfield areas has been proposed.

Vorticity Estimation of the Terrane Boundary Shear Zone of the Eastern Ghats Mobile Belt, and its Tectonic Significance

ABSTRACT The Terrane Boundary Shear Zone (TBSZ) of the Eastern Ghats Mobile Belt on the NW front against Bastar Craton shows northwesterly vergent thrust kinematics; and on the northern front with Singhbhum Craton shows dextral strike-slip tectonics. The kinematic vorticity numbers are as follows: the NW front, Wm(RGN) is 0.70–0.83 and Wm (Rs/ θ ) is 0.82–1.0; and the northern front, Wm(RGN) is 0.60–0.81 and Wm(Rs/θ) is 0.61–1.0. The estimates suggest that the Wm (Rs/ θ ) values are larger which indicates that the last incremental strain is dominated by simple shear. Further, both fronts are deformed by transpressional to simple shear deformation. However, the northern boundary shear zone has a transtensional component suggesting the TBSZ has undergone shear zone perpendicular extension. The development of the Mahanadi rift valley on the northern front may be related to such extension.

Uncovering the hidden architecture of the Rengali Province, eastern Indian shield using high-resolution aero-geophysics, ground-gravity, structure: Insights towards geology and tectonics

The Rengali Province is a shear zone bounded discrete domain of amalgamation among two Archean Cratons viz. the Singhbhum and Bastar cratons and a mobile belt namely Eastern Ghat Mobile belt. Based on geological evidences, it also displays an India-Antarctica connection in the past geological time-slice and supports supercontinental reconstruction. Although, the tectonothermal evolution of this province has been largely probed based on lithological, structural and metamorphic accounts, however, correlative geophysical-geology integration is absent. Hence, we analyze and interpret newly acquired high-resolution aero-geophysical data for the first time. The interpretations of high-resolution aero-geophysics, ground gravity and radiometric anomaly have been connected with geology to provide insights into tectonic evolution. Multi-scale geological-geophysical-structuralanalysis has been employed for understanding the subsurface architecture and contact relationship with the nearby cratons-mobile belt. Based on the aero-magnetic signature, three different zones have been delineated viz. northern, central and southern zones within the Rengali Province. The three zones are characterized by their distinct geophysical fabric and further are correlated with the geology. The gravity anomaly and modeling suggest the presence of a high-density body at mid-upper crustal depth (∼5–10 km). Three major shear zones, viz. the Barakot, Riamal and Kerajang delineate the bounding surfaces of the Rengali Province. However, the current geophysical signature indicate that the western part of the Kerajang Fault zone (KFZ) shares an inter-domain status between the Rengali Province and the Bastar Craton while the eastern part showcases an intra-domain character. Based on the complex series of magnetic fabric and anastomosing geophysical (particularly, magnetic) signature, the Rengali Province (RP) displays a classical signature of multiple accretionary histories supported by various episodic tectono-thermal activities at different time-slices.

Evidence of a Proterozoic suture along the southern part of Eastern Ghats Mobile Belt: Implications for the Nuna supercontinent

Evidence of a Proterozoic suture along the southern part of Eastern Ghats Mobile Belt: Implications for the Nuna supercontinent

Anisotropy of magnetic susceptibility and rock magnetism of high-grade rocks from Eastern Ghats Mobile Belt, India: Constraints to tectonics

Anisotropy of magnetic susceptibility and rock magnetism of high-grade rocks from Eastern Ghats Mobile Belt, India: Constraints to tectonics

Apatite-hosted REE mineralization in the Eastern Ghats Mobile Belt: A future prospect for REE

The growing need of rare earth elements in different sectors of the modern-day world has led to their increasing demand, which is in accordance with their limited supply. In such a scenario, investigations related to search for potential zones of rare earths have become the need of the hour. In one such investigation, undertaken by Geological Survey of India, the authors report profuse intrusion of the apatite veins into the syenite-pyroxenite suite in the eastern part of the Eastern Ghats Mobile Belt (EGMB) in Nayagarh area of eastern Odisha. These apatite veins are anomalously rich in REEs, particularly LREEs, which on average ranges between 37,000 to 53,000 ppm. Rare earths and apatite are generally directly proportional, where apatites tend to carry sufficient REE budget, depending on the phosphorous fugacity and other ambient conditions inducing their genesis. The major-oxide chemistry of apatite veins indicates that apatites in the study area can be divided into two types based on SiO2 wt.% and their inverse relationship with P2O5 and CaO wt.%. Mineral chemistry data shows overall SiO2 depletion, with dominance of CaO, followed by P2O5. Apatite veins, as per mineral chemistry, contain numerous veinlets (identified microscopically), where one type is REE-bearing and another type is REE-free. The REE-bearing phases are rich in Ce, Nd, La and Pr and are represented by allanite, monazite, and bastnaesite. Thorite and zircon are prevalent. Earlier instances of apatite intrusions into granulite have been reported from parts of south India. On the contrary, in this area, the intrusion is typically restricted to the younger intrusive units of the EGMB, represented by syenite-pyroxenite suite. The intrusives also show moderately high values of REEs. In this paper, an attempt has been made to characterize the apatite veins and the syenite-pyroxenite suite, they have intruded, in respect to their mineralogy and tectonics and to elucidate the potentiality of the area in terms of future REE exploration.

Paleozoic to Mesozoic paleotectonic reconstructions of Gondwana assembly: Insights from petrography, heavy mineral chemistry and detrital U–Th–total Pb monazite geochronology of sandstones in the Pranhita-Godavari Basin (SE India)

The provenance study of Paleo-Mesozoic sediments of the Pranhita-Godavari (P-G) Basin, located in the southeastern India is crucial for the reconstruction of the eastern Gondwanaland, including the India-Antarctica connection. This study examines petrography, heavy mineral chemistry and detrital monazite geochronology of the Permo-Carboniferous to Cretaceous, predominantly fluviatile sandstones in the P-G Basin to track the possible sediment sources in East Antarctica and Eastern India. The sandstones show a gradual shift in composition from feldspatho-quartzose to quartzose arenite from older to younger succession, accompanied by a change in source terranes in a changing setting from transitional continental to the cratonic interior. The heavy minerals of the sandstones are dominated by garnet, rutile, ilmenite, monazite and zircon in order of decreasing abundance. The mineral chemistry of garnet and rutile indicates the predominance of sources from amphibolite to granulite facies rocks with minor inputs from metapelitic sources. The increase in textural and mineralogical maturity of sandstones accompanied by a gradual increase in ilmenite alteration from the bottom to the top of the succession indicates the attainment of tectonic stability with time. U–Th–total Pb dating of detrital monazites yielded three distinct major clusters at (1) 2556–2125 Ma, (2) 969–715 Ma, and (3) 581–418 Ma. Based on the correlation of source composition and monazite geochronology and paleocurrent data, the source of sediments is traced to the orogens of the Eastern Ghats mobile belt, East Antarctica (including Rayner and Napier complex), Karimnagar granulite belt, Khammam schist belt, and Bhopalpatnam granulite belt, situated to the west, south, and southeast of the present outcrops of the P-G Gondwana succession. The younger age populations possibly represent the sediment input from Kuunga Orogen, which represents the youngest orogenic event (635–488 Ma) in the Gondwana assembly. The rocks of Kuunga orogeny, occurring to the south of the basin, was a minor contributor to the P-G Gondwana sediments of this basin. The new data supports that the Eastern Ghats Mobile Belt of India and East Antarctica were conjugate to each other till the Late Triassic Period, both of which contributed major sediments to the P-G Gondwana Basin.

Provenance of low-grossular–high-pyrope detrital garnets from beach sands of East Coast of India between Gosthani and Vamsadhara rivers

Major element compositional spectrum, formation in diverse magmatic and metamorphic rocks, and relative stability during sediment transport, burial, and diagenesis make garnet an important indicator of sedimentary provenances. However, a fundamental question yet to be answered is whether the low-grossular–high-pyrope detrital garnets reflect source characteristics or record sedimentary processes. To address this problem, we have analysed garnets from the beach sands of the East Coast of India and in the source lithologies of the catchment area within the Eastern Ghats Mobile Belt. Investigated garnets show a broad compositional spectrum; most garnets are dominated by almandine49–86% with variable contents of pyrope9–47%, minor grossular0.8–15%, and low spessartine0.5–4%. Using multiple proxies, including a state-of-the-art machine-learning-based garnet discrimination scheme, we found that 96 % of analysed beach sand garnets are of metamorphic origin and 4 % igneous. Amongst the metamorphic garnets, 85 % were derived from granulite facies, 5 % from eclogite/ultrahigh-pressure facies, 5 % from amphibolite facies, and 1 % from blueschist/greenschist facies rocks. Concerning host-rock bulk composition, 93 % of garnets belong to intermediate–felsic/meta-sedimentary class and 7 % belong to the mafic category. The chemistries of the beach sand detrital garnets of the East Coast of India are readily coupled with the compositions of the garnets from source rock lithologies of the Eastern Ghats Mobile Belt. Very low-grossular garnets are derived from meta-pelitic rocks (khondalites) and mafic granulites, whereas slightly grossular-rich garnets are derived from charnockites. The present study indicates that the low-grossular–high-pyrope detrital garnets are vital signposts of sedimentary provenances. We advocate that the high P-T granulite facies mobile belts are distinctive sources for the low-grossular–high-pyrope detrital garnets.

Magmatic and Geochemical Studies of Early Neoproterozoic Koraput Anorthosite Massif, Eastern Ghats Mobile Belt and their Implications for Rodinia Assembly

Abstract 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 ~1000°C and ~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.

Geochemical and geochronological evolution of the UHT granulites from the Eastern Ghats Mobile Belt, India: implications from F-OH substitution in biotite, thermal events and cooling age

ABSTRACT The thin lenses and bands of ultra-high temperature (UHT) granulites with diagnostic sapphirine and quartz in contact are occasionally found on the western flank of the Eastern Ghats Mobile Belt (EGMB), which inherits the suturing and over-thrusting signatures of the EGMB with the Greater Indian Landmass (GIL). The mineral biotite contains an abnormally high fluorine concentration, as revealed by the geochemical examination of these granulites from the research area (Kothuru), which was caused by the F-OH substitution to withstand extreme thermal metamorphic conditions. The geochemical results from the multi-element spider diagram and the Harker’s variation diagram with primitive-mantle normalization also show an enrichment of light rare earth elements and large-ion lithophile elements over depleted heavy rare earth elements and high-field strength elements. An evolutionary history has been established for the high-grade rocks that were subjected to ultra-high temperature metamorphism, based on the geochemical signatures of the examined granulites. The use of isotopic K-Ar cooling ages and electron microprobe monazite chemical ages of the thermal episodes, which act as useful tools to explain the time and span of the polycyclic metamorphic terrane, is another significant component of the current work. Numerous researchers have attempted to estimate the thermal episodes in various areas of the Eastern Ghats Mobile Belt, but their cooling ages are still poorly understood. Consequently, two thermal episodes that happened at 842 Ma and 637 Ma ago, as well as a cooling age of about 448 Ma that marked the quick exhumation of the high-grade rocks under study, have been recorded in the current investigation. The association between the Greater Indian Landmass and Eastern Antarctica during the existence of the Rodinian supercontinent has been established by recorded geochronological events.

Geochemistry of Stream Sediments from Eastern Ghats Mobile Belt, India: Implications on Sediment Type, Maturity, Source-area Weathering and Provenance

Abstract During their flow through an area, the streams are used to erode, transport and re-deposit sediments in the number of cycles following the climatic variation in an area. This cycle in turn affect the chemistry of these sediments and hence the geochemical study of these sediments helps to understand the palaeo-climate, source-area weathering and provenance of the study area. In order to understand the geochemical classification of sediments, palaeoclimate, source-area weathering and provenance for stream sediments of the Eastern Ghats Mobile Belt (EGMB), 364 stream sediment samples were collected from the area around Daringbadi, Kandhamal district, Odisha, India and analyzed for major oxides, trace elements and rare earth elements. These sediments are geochemically classified as shaly and wacke type, moderately mature and derived through the high intensity of weathering of source rock under warm and humid climatic condition. The positive correlation between Al2O3 and Fe2O3, MnO, and MgO, indicates multiple sources for sediment and these oxides are associated with clay minerals. The discrimination function diagram suggests a felsic igneous as well as quartzo-sedimentary provenance for these sediments whereas the ratio of Al2O3/TiO2 and concentration of V-Ni-Th suggest a felsic igneous source rock. The high concentration of LREE, slight enrichment of HREE and negative Eu anomaly indicate terrestrial or continental crust source rock. Hence the source rock for these sediments are granite gneiss, charnokite and khondalite present in and around Daringbadi area.

Mechanical strength and nature of lithospheric deformation beneath the rifted sedimentary basins of the east India passive margin

The study of gravity signatures corresponding to sediment load over the passive margins is helpful to constrain the mechanical properties of continental rift systems as well as the adjacent ocean basins. Seismic reflection, free-air gravity and well information from the East India Passive Margin (EIPM) are investigated through spectral approach and 2D process-oriented gravity modelling for quantifying effective elastic plate thickness (Te) to understand the rift mechanisms and the sedimentary basins evolution. The characteristics of lithosphere within the major structural domains along the margin are quite variable. A narrow necking zone (40 km) in the southern segment, and approximately a 70 km hyper-thinned and exhumed domains are inferred in the central segment, while a narrow hyper-thinned domain (30–35 km) is observed in the northern segment of the margin. The southern segment of EIPM, adjacent to Southern Granulite Terrain has low Te values ranging from 5 to 10 km. The segment in the central margin, offshore Dharwar Craton has moderate Te values of 15–20 km. And the northern segment adjacent to onshore Eastern Ghats Mobile Belt has relatively high mechanical strength with Te values ranging from 25 to 35 km. The pattern of Te values and extent of major structural domains along the margin indicates that the southern, central and northern segments evolved as three different modes of rifting such as transform, hyperextended and hypoextended, respectively. In the oceanic domain, the lithospheric strength broadly increases with age following the thermal induced cooling plate model (600 °C isotherm). The thick sedimentary basin of the Bay of Bengal had attained the high value of elastic thickness (Te > 45 km) in the last 23 Myrs. The significant rheological strengthening of the oceanic lithosphere may be attribute to the following reasons: 1) increase in shear-wave velocity anomaly at a depth of 150 km and upper mantle density, 2) change in plate curvature caused by excessive deposition of Bengal Fan sediments in the deep ocean basins and subduction of oceanic plate under the Eurasian plate near the Bengal Fan and 3) modification of stress state of the lithosphere as a convergent interaction of the Indian plate with SE Asia.

A detailed gravity picture of Nallamalai Fold Belt–Nellore Schist Belt (NSB) of Eastern Dharwar Craton with marginal Eastern Ghats Mobile Belt in Krishna Region, South India with special reference to Late Archaean NSB evolution

A detailed gravity picture of Nallamalai Fold Belt–Nellore Schist Belt (NSB) of Eastern Dharwar Craton with marginal Eastern Ghats Mobile Belt in Krishna Region, South India with special reference to Late Archaean NSB evolution

Metamorphic evolution of the UHT granulites from Mandikota, Eastern Ghats Mobile Belt, India: Constraints from phase equilibria modelling, fluid inclusions and monazite U-Th-total Pb geochronology

The Eastern Ghats Mobile Belt (EGMB) had been subjected to extreme thermal metamorphic history at various sections of its terrane. One such terrane (Mandikota) located near the western part of the EGMB has been speculated based on asserted reaction textures, conventional geothermobarometry, geochronology, fluid inclusions, and pseudosection modelling. The present integrated study aims to understand the intricacies of the diversified and controversial tectono-metamorphic evolution of these polycyclic granulite terranes. The stable occurrence of sapphirine + quartz in contact is rare in its own and is a diagnostic feature of Ultra-High Temperature (UHT) metamorphism. Conventional geo-thermobarometeric tools applied, suggests an ordered series of reactions for the different stages of metamorphism experienced by the investigated granulites. Also, the P-T estimated by conventional methods lies in sound correlation with the peak P-T condition (in excess of 950 °C at nearly 9 kbar) attained in the constrained pseudosection model. The exhumation trajectory of the examined UHT terrane reflects P-T path responsible for the thrusting mechanism with isothermal decompression of 3 kbar followed by late-stage isobaric cooling. This study also presents the primary report for the systematic fluid inclusion study of the UHT granulites and its correlation with the evolved P-T trajectory. In addition, monazite dating using Electron Micro Probe Analysis (EPMA) is procured to assess the time frame in understanding the P-T-t evolution of the high-grade terrane. The geochronological study further revealed a new age (∼600 Ma) associated with the Visakhapatnam Domain which adheres to the Pan-African orogeny and marks the reworking phase of the widely reported the Grenvillian event in the EGMB province. As such, the results from the studied fluid inclusions displaying monophase inclusions of CO2-rich carbonic fluid, and its corroboration with the P-T pseudosection model interpreting the phase equilibrium conditions prevailing during the Neoproterozoic time (∼900 Ma).

Fretful Longevity of Upper Kolab Reservoir, Odisha by GIS Study

Background: The nonrenewable energy source, hydropower reservoirs are the yardstick that scales up developing countries around the globe including India. The multipurpose Upper Kolab project is housed at the Kondhan Hills of the north Eastern Ghats mobile Belt range near Koraput Town. The dam is of length 630.5m with a height of 54.50m, and an average annual flow1803 M cum in operation since 1986. The project was built for 320MW generation, about 445000Ha CCA, and water supply to nearby towns.
 Objective: Climate Change and anthropogenic stresses have resulted in depleting the major reservoir’s capacity by sedimentation, hence irrigation and power generation. The southern part of the Northeastern Ghats belt is worst affected. The present study is about the rate of capacity loss of Upper Kolab Reservoir in south Odisha.
 Methodology: The present study involves the collection of data from the Landsat 4, Landsat 5, and Landsat 8 OLI Operational land user image of 30 m resolution was downloaded from either SRTM data or Earth Explorer data, and the digital elevation model (DEM) was prepared for the same period of the years 1996, 2002, 2013, 2017 and 2021. The TOPO geological map (1:500,000 scale) of 1983 was used to digitize geological formations. The ArcGIS 10.2 software is used for the topographic constraints of the water body and its watershed. The maps generated are slope maps, aspect maps, and various differentials sediment values in volume and water spread area.
 Results and Conclusion: The inference is the fast rate of annual sedimentation @3.542mm/yr which is much higher than its mother basin Godavari (@2.22mm/yr. The longevity of the Upper Kolab Reservoir and power generation shall be affected earlier before it is designed life. Sedimentation needs prioritization, as caused by the anthropogenic and climate-induced huge sediment entry to the upper Kolab reservoir warranting a secondary reservoir downstream.

Origin and evolution of vanadium‐rich oxide and titanite phases in lamprophyre and mafic dykes from the Nuapada diamondiferous Lamproite field, BastarCraton‐EasternGhats Mobile belt contact, India: Metallogenic and geodynamic implications

Transitional boundaries of the craton and mobile belt mark diverse and long‐term tectono‐thermal events like hot and cold lithospheric contact, back‐arc‐type subduction, and also constitute a favourable locale for metallogeny. The exact nature and origin of such metallogenic enrichment in the lithospheric mantle source beneath contact zones are still uncertain. The contact of Bastar Craton and the Eastern Ghat Mobile Belt (EGMB), India, provides an ideal geological setup to study the metallogenic enrichment processes. In this study, we present a detailed petrographic and mineralogical investigation of various iron oxide phases and titanites in spatially and temporally distinct lamprophyre and mafic dykes from the diamondiferous Nuapada Lamproite Field (NLF) at the contact between Bastar Craton and EGMB. Diverse textural assemblages of oxides, namely, trellis, sandwich‐type exsolutions and reaction–replacement, are widespread. Ilmenites, magnetites and titanites from the mafic dykes as well as lamprophyre exhibit an anomalous enrichment of vanadium (V2O3up to 3.7 wt%), whereas ilmenites are also characterized by their elevated manganese content (MnO up to 3.8 wt%). Mineral chemistry‐based plots and thermo‐oximetric studies suggest the magmatic origin of iron oxides belonging to the Fe–Ti–V‐type ore in which partitioning and sequestration of the elements were controlled by differential crystallization, exsolution and fractionation rather than any imprints of contamination. Multiphase sequestration of vanadium as well as manganese in lamprophyre and mafic dykes, separated in space as well in relative depths of origin, signifies the presence of a fertile mantle. The role of subduction‐derived metasomatized fluids as a causative factor of vanadium metallogeny in this domain is evaluated. Low‐Mg and high‐Mn ilmenites of this study are consistent with the reported occurrences of diamonds from the NLF and adjoining areas of the Bastar Craton.

Estimation of Moho Depth Beneath Southern Indian Shield by Inverting Gravity Anomalies Constrained by Seismic Data

AbstractThis study presents a high‐resolution 3D Moho structure beneath southern India and its surrounding regions from observed gravity anomalies. The global gravity disturbance model (XGM2019e) with a grid resolution of 0.1° is considered for this study. The extended Bott's inversion algorithm and Gauss‐Fast Fourier Transform based forward model are adopted to invert for the Moho undulations beneath the Indian peninsula. The inversion algorithm is tested for a synthetic model having a predefined density contrast and mean Moho depth. The robustness of this inversion algorithm is further tested for noise‐incorporated gravity data. The control points are required for estimating two hyper‐parameters, viz. density contrast, and reference depth, which play a crucial role in the precise estimation of Moho depth. In real case study, the inverted Moho depth of Southern India and its surrounding regions by seismic constraint receiver function‐driven control points show a very complex architecture of Moho topography. The observed average crustal thickness in the study region is 35.35 km, corroborating with the previously reported Moho depths. The maximum crustal thickness is 53.04 km beneath the southern part of Archean Western Dharwar Craton and west of Salem block, around 44–47 km Moho depth is observed at the south of Salem block into Madurai block till Achankovil Shear Zone, which suggests the possible continuation of the Achaean crust of Palghat‐Cauvery Shear Zone System. The lowest crustal thickness values are observed along the eastern margin of the Cuddapah basin, which overlaps with the Proterozoic Krishna basin of the Eastern Ghats Mobile belt.

New insight into the tectonic setting of fault-bounded Indian Gondwana coal basins from U–Pb detrital zircon provenance ages of the Bokaro and Jharia basins, central east India

AbstractA detrital zircon U–Pb laser ablation–inductively coupled plasma–quadrupole mass spectrometry (LA-ICP-QMS) provenance study was undertaken on samples selected from the Lower Gondwana successions preserved in the fault-bounded Bokaro and Jharia basins in India to investigate the provenance of the sediment and determine whether the strata were deposited in isolated syn-depositional graben basins or formed part of a wider regional depositional system. A total of 730 concordant U–Pb detrital zircon ages revealed six distinct age fractions: (i) a latest Neoproterozoic to earliest Cambrian age fraction (530 to 510 Ma), which tails down in some samples to older Neoproterozoic ages (650 to 630 Ma); (ii) a major age fraction with an age peak of earliest Neoproterozoic (950 Ma), accompanied in some samples by a twin Mesoproterozoic peak (1000 Ma); (iii) a middle Mesoproterozoic age fraction (1330 to 1300 Ma); (iv) a prominent earliest Mesoproterozoic zircon age fraction (1600 Ma); (v) a less well-defined late Palaeoproterozoic zircon age fraction (2100 to 1700 Ma, or 1600 Ma); and (vi) an Archaean zircon age fraction that typically comprises two zircon age fractions, namely zircons with early Neoarchaean ages (2800 to 2750 Ma) coupled with zircons with ages older than 3100 Ma. Comparison of these newly obtained age fractions with detrital zircon age data presented by Veevers & Saeed (2009) shows similarities with the Gondwana strata of the Mahanadi and Pranhita–Godavari basins, implying that strata preserved in the fault-bounded Gondwana basins in central east India formed part of a much wider regional depositional system and that they were not deposited in isolated half-graben or graben basins. Potential source regions to the Gondwana strata of the Bokaro and Jharia basins include the Eastern Ghats Mobile Belt and rock units in Antarctica.

Lithospheric architecture below the Eastern Ghats Mobile Belt and adjoining Archean cratons: Imprints of India-Antarctica collision tectonics

The investigation of the rigid lithospheric mantle architecture floating over the weaker hotter asthenosphere is key to understanding the plate tectonic evolution of the Eastern Ghats Mobile Belt and the adjoining Archean cratons. We present shear-wave velocity (VS) structure for the crust and upper-mantle below the Eastern Ghats Mobile Belt (EGMB) and adjacent Archean cratons. The lithospheric structure is constrained through 4–150 s fundamental-mode Rayleigh and Love-wave group velocity dispersion measurements, using regional (2°–30°) earthquakes recorded at 27 seismic stations installed along two distinct profiles. Velocity models are improved by joint inversion of resultant dispersion curves with receiver functions computed from the teleseismic P-waves. Observed variations in crustal and lithospheric architecture across the domains of the Eastern Ghats Province are implication of the deformations due to rifting and collision of India and East Antarctica in the context of assembly and breakup of Rodinia and Gondwana supercontinents. The cratons and the mobile belt are characterised by 34–38 km, ∼45 km thick heterogeneous crust and 120–160 km, 90–120 km thick lithospheres, respectively. The abrupt changes in the crustal thickness owes its origin to the collisional thrusting of the Eastern Ghats Province against the Archean cratons. Significant variations in the nature of Moho are also noted. The flat sharp cratonic Moho is distinct from the gradational Moho below the Eastern Ghats Province, possibly a signature of magmatic underplating below the mobile belt. The nature of the lithosphere-asthenosphere boundary (LAB) interpreted from the gradient change in velocity appears to be poorly-resolved. Therefore, we utilise radial anisotropy determined from the discrepancy between VSH and VSV based on Rayleigh and Love-wave velocities respectively, as a proxy. Our findings confirm the LAB through positive radial anisotropy (VSH > VSV) prevalent in the asthenospheric-mantle that is likely explained by flow-induced shear. Overall, the lithospheric architecture below the study area has been shaped through several deformational episodes that distinguish the multiple litho-tectonic units within the mobile belt. The loss of cratonic lithospheric keel can be attributed to the mantle plume given the Gondwanan trajectory of the Indian subcontinent over Kerguelen and Crozet hotspots.

Tracing thermal and non-thermal water circulations in shear zones of Eastern Ghats Mobile Belt zone, Eastern India- inferences on sustainability of geothermal resources

The development of the geothermal resources in India has not progressed mainly due to inadequate understanding of the deeper thermal regime and uncertainty over the sustainability of heat source. In this study, isotopes, hydrochemical techniques and integrated geothermometric models have been applied to a low-medium enthalpy geothermal system belonging to shear zones of Mahanadi graben, Eastern Ghats Mobile Belt (Eastern India) to gain better insights. Isotope results indicate that thermal waters are meteoric in nature and absence of δ18O-shift suggests that the subsurface temperatures are below 200 °C. Distinct isotopic and hydrochemical signatures of thermal waters clearly suggest their origin from different geothermal reservoirs. Thermal waters at Atri/Tarabalo sites are derived from the southern part of the graben while at Athmalik, from northern part. Away from graben in southern direction (Taptapani site), the thermal waters are derived from rain occurring at elevated regions. Seasonal variations in chemical and isotope data are minimum in thermal waters. The estimated reservoir temperatures range between 92 and 124 °C with reservoir depths 1.6 – 2.4 km. Tritium data suggests that thermal waters are old and have 12–63% mixing with non-thermal water. The modelled radiocarbon age of thermal waters (13.3 – 20.7 Ka) suggests paleo-recharge of the reservoirs during Last Glacial Maximum (LGM), characterized by arid climate and low rainfall. A conceptual isotope model illustrating the genesis and circulation patterns of thermal and non-thermal waters is presented. The study highlights the potential of isotope-based studies in expanding the geothermal energy utilization in India.