Saibal Gupta

Abstract: The Koraput Alkaline Complex (KAC) lies on the NE-SW trending Sileru Shear Zone (SSZ) separating the Proterozoic Eastern Ghats Province from the Archaean Indian craton. The core of the KAC is made of hornblende gabbro, which is rimmed by a band of nepheline syenite in the east and syenodiorite in the west. The timing of magmatism with respect to the SSZ is disputed. The KAC was deformed during emplacement, and a magmatic foliation related to the syn-emplacement deformation, D1, is present in the gabbroic core. The dominant D2-related field fabric strikes NE-SW and is penetrative in parts of the gabbro and marginal lithologies. E-W trending D3 shear zones cut across the complex. Distinct textural domains resulted from strain partitioning during deformation. Parts of the complex with magmatic textures constitute Domain-1, while D2 and D3 fabric zones comprise Domains-2 and 3 respectively. Temperatures in the KAC initially decreased following D1, but increased through D2 and ...

Abstract The discovery of iron-bearing concretions is one of the most exciting discoveries in the recent past on Mars. We report here an analog terrestrial site hosting hematite-bearing concretions belonging to Jhuran sandstone, Kutch, India. Based on petrography, mineralogy, geochemistry and spectral studies (Visible Near Infrared: VNIR and Mossbauer), we show very good similarity between the Jhuran concretions and the “Martian blueberries”. The Jhuran and Martian concretions share similar textural attributes and are of comparable size, but are geochemically different. Based on VNIR study, the mineralogy of the concretions is constrained to comprise hematite, goethite and kaolinite; however, Mossbauer spectra could not detect the pure hematite phase, and instead, suggest the presence of a poorly crystalline mixture of goetheite and hematite. Thus, the Jhuran concretions are most commonly mixtures of goethite and hematite, and not pure hematite. The enrichment of Ni within concretions as compared to the host sandstones is also comparable with the reported Ni-enrichment of Martian concretions. We propose sedimentary diagenesis as the most feasible process that can explain incorporation of Ni into the concretions by coupled substitution in the iron oxide structure. This is inconsistent with the cosmic spherule hypothesis to explain Martian concretion formation, and instead, sedimentary diagenetic processes appear more likely. Finally, the morphology, texture, geochemistry and spectroscopic investigations suggest that the Jhuran iron concretions most likely formed due to sedimentary diagenetic processes, similar to inferences from other Martian analogue localities. Therefore, this study has relevance for understanding the formation processes of Martian blueberries and diagenetic processes on Mars. The Kutch area also has geological similarity with other aspects of ancient Mars and could be a potential testing site for carrying out future Mars exploration studies on Earth.

<p>Hot springs in the stable Indian shield are non-volcanic in origin. Atri and Tarbalo are two such hot springs in the Eastern Ghats Province (EGP), Eastern India and these are characterized as part of a low enthalpy geothermal system. Stable isotopic, geochemical and geothermometric studies were carried out on these two hot springs as well as on the groundwater of this region to understand the origin and evolution of these non-volcanic hot springs as well as subsurface water system in terms of the source of the dissolved solute in the water, mixing processes and the residence time of the thermal and non-thermal waters. Surface temperature of the slightly alkaline hot spring waters ranges from 45 to 58 °C. Temperature of the cold groundwater, collected from tube and dug well varies between 28 and 32 °C. A distinct hydro-chemical difference can be interpreted from the major ion concentrations of hot waters and non-thermal waters. Hot spring waters have higher concentrations of sodium, potassium and lower calcium, magnesium than cold water. While the hot springs waters are enriched in Cl<sup>-</sup> and F<sup>-</sup> and cold waters are rich in bicarbonate. The low bicarbonate concentration of thermal waters may indicate that the hot spring reservoirs have no atmospheric effect. Definite geochemical differences between these two types of water suggested that there is no mixing between hot spring water and cold groundwater. Thermodynamic calculations suggest that mineral dissolution is the predominant evolutionary mechanism for the thermal and non-thermal waters and these waters hold a partially equilibrated state with the surrounding rocks. Bivariate plots of the major ions also indicate that silicate weathering is the dominant mechanism controlling solutes concentrations in the cold water whereas evaporite dissolution more likely involves in the evolution of hot spring water. The measured stable isotope ratios (δ<sup>2</sup>H and δ<sup>18</sup>O) of all the hot and most of the cold-water samples plot along the Global Meteoric Water Line (GMWL), indicating their meteoric origin where as some cold waters show evaporation effect which suggests atmospheric influence. Tritium and <sup>14</sup>C ages indicate that the cold waters are relatively modern, while the hot waters have a longer residence time of about 5000 years. Based on the chemical characteristics of the hot waters Na-K thermometer, Na-K-Ca thermometer and silica (quartz) thermometer were used to estimate the reservoir temperatures. Cation and silica geothermometers yield similar estimation of the reservoir temperature between 125 -150 °C for hot spring waters. Results of geochemical (numerical) modelling of water-rock interaction in this region, using PHREEQC, are consistent with hydrochemical analysis. Inverse modelling and saturation indices of minerals indicate that water chemistry in this region is controlled by the dissolution of feldspar and saturated with kaolinite, gibbsite and fluorite. This equilibrium is attained in the thermal waters, which therefore show a more restricted range of composition than the non-thermal, colder waters. The higher fluoride concentration in the thermal water may also be attributed of chemical equilibrium with the enclosing host rock.</p>

AT KACHCHH: IMPLICATIONS FOR MARS. S. Mitra, S. Gupta, K. Mitra, S. Bhattacharya, R. Chakrabarti, D. Ray, S. Banerjee, P. Chauhan, and G. Parthasarathy, Department of Geology & Geophysics, Indian Institute of Technology, Kharagpur – 721 302, India, Space Applications Centre, Indian Space Research Organization, Ahmedabad – 380 015, India, Centre for Earth Sciences, Indian Institute of Science, Bangalore 560012, India, Physical Research Laboratory, Ahmedabad380 009, India, Department of Earth Sciences, Indian Institute of Technology Bombay, Mumbai-400076, India, National Geophysical Research Institute (CSIR), Hyderabad – 500 007, India.

Abstract The Eastern Ghats Province (EGP) of India is considered to have been a part of the supercontinents Rodinia and Gondwana at c. 1.0 Ga and 500 Ma, respectively. A range of ages spanning much of the Neoproterozoic have been periodically reported from parts of the EGP, indicating that the terrane remained tectonically active in the interval between Rodinia and Gondwana amalgamation, although the nature of the associated events remains uncertain. In this study conducted on the northern EGP, we constrain these enigmatic events from structural (field, microstructural and Electron Backscatter Diffraction studies), metamorphic (pseudosection modelling and geothermobarometry) and geochronological (monazite chemical dating) evidence. The area is multiply deformed, with the D1 and D2 shortening deformation accompanying granulite facies metamorphism that peaked at temperatures in excess of 900 °C, at ~955 ± 28 Ma. Following hydrous fluid infiltration at ~808 ± 10 Ma, the entire northern EGP was affected by an extensional deformation event D3 that reoriented all earlier fabrics into an E-W trending, northerly dipping orientation. Deformation microstructures and results of geothermobarometry indicate that D3 operated at around 600 °C at ~711 ± 18 Ma. Dextral strike-slip deformation (D4) along the Mahanadi Shear Zone operated under greenschist facies conditions and did not reset monazite isotope systematics in the region. The signature of mid-crustal extension during D3 is likely to be associated with the break-up of Rodinia. The lack of corresponding evidence for mid-Neoproterozoic extension in the adjacent Indian cratons suggests relative uplift of the EGP following Gondwana amalgamation.

On the island of Sikinos in the Cyclades a schistose carapace separates a marble-blueschist cover sequence from underlying basement rocks. The basement ‘core’, comprising metapelitic gneisses, biotite-bearing granodiorites and aplites, becomes increasingly strained towards the carapace with progressive obliteration of earlier structures and intensification of a mylonitic foliation that becomes pervasive within the carapace. Granodiorites in the ‘core’ can be traced into microcline schists within the carapace, whereas metapelitic gneisses are converted to garnet-mica schists. The carapace is therefore a simple shear zone comprising basement rocks mylonitized during overthrusting of the cover.Biotite clusters in granodiorites of the basement ‘core’ are partially altered to phengite, whereas plagioclase shows incipient sericitization. In more strained rocks these hydration reactions show enhanced progress, until biotite and plagioclase are finally eliminated in the carapace. Rare glauc...

The Kachchh Basin is a peri-cratonic rift basin in western India, exposing a vast range of diverse geologic features representing the past 200 million years spanning from the Jurassic Period to the recent. The Basin represents highly rugged terrain in the form of the hilly ranges and pediment surfaces, while the flat terrain in the north is expressed by the low-lying Rann and Banni plains (mudflats, marshes, and grassland). This basin has preserved several classical terrestrial analog sites to study planetary science. Several potential localities in the basin provide opportunities to explore as Martian analogs. In the present study, we have proposed five analog sites from the Kachchh basin that has preserved classical geomorphic feature (volcanic and impact craters) as well as minerals (primary phyllosilicates, secondary hydrous sulfates, precipitated iron minerals, evaporite, and liquid brines like perchlorates) that tell the tale of the geological activity taken place on the Mars. The cultural and ecological aspects of the proposed sites and their hinterland are also discussed for the tourist attractions. All the proposed sites have ample geoheritage potential and need strong attention for conservation. Further, the establishment of geoparks and development of geotourism in the proposed area will enhance the Earth and Planetary Sciences scenario apart from boosting of local economy, including helping activities, research funding, and employment opportunities for locals that will play a significant role in the economic development of the region. To achieve such an ambitious program and accomplish the Sustainable Development Goals, these locations should be conserved and extended for geotourism.

Abstract Shear zone kinematics are interpreted from sections (X-Z) parallel to the stretching lineation (X-direction) and perpendicular to the mylonitic foliation (X–Y). The stretching lineation is a product of finite strain, defined by minerals or mineral aggregates that deform plastically. In quartzofeldspathic rocks deformed below 600 °C, rheological contrasts between quartz and feldspar are amplified, and the mesoscopic stretching lineation in the shears may be indistinct in outcrop as quartz ribbons anastomose around relatively competent feldspar clasts. In high strain-rate zones, rheological contrasts between these minerals are reduced and a stretching lineation suitable for kinematic interpretation develops. In late amphibolite and greenschist facies shear zones transecting pre-lineated quartzofeldspathic granulites of the Eastern Ghats Province, India, the stretching lineation represents the resultant of pre-existing stretch and superposed increments of later shearing. Until the stretch accumulated in the X-direction of the later deformation exceeds the earlier finite stretch, the pre-existing stretching lineation progressively rotates towards the later X-direction with decreasing aspect ratio. These intermediate lineation orientations, have no kinematic relevance to either earlier or later deformations. This example highlights the importance of temperature, strain rate and orientation of pre-existing stretching lineations in the appearance and kinematic interpretation of,stretching lineations in ductile shear zones.

... of Geology & Geophysics, IIT, Kharagpur 721 302 (India ... Unplanned urbanization also does not appear to be a major cause of land slips within the study area as most of the slide zones are sparsely populated ... The rockslides at the top of Pagla Jhora (Gita Pahar) in Darjeeling (Fig ...

The dataset consists of Electron Backscatter Diffraction (EBSD) data in .crc format, generated from quartzite samples at 0.5 micron and 1 micron step sizes. The quartzites are from the Rengali Province and Eastern Ghats Province; these are important geological terranes that comprise part of the Indian shield. Fine grained quartzites have been scanned at 0.5 micron step size and coarse grained quartzites have been scanned at 1 micron step size to ensure that orientation contrasts due to subtle lattice modifications in grain boundary domains have been adequately documented.

The Eastern Ghats Mobile Belt (EGMB) lies to the east of the Archaean Bastar and Dharwar Cratons, and to the southeast of the Singbhum Craton in the Indian shield. Along its western boundary, the EGMB granulites have been thrust westward as a nappe over the Bastar Craton along a mylonitic contact zone. Earlier studies considered the northern boundary of the EGMB with the Singhbhum Craton to be a thrust, although this interface is geometrically parallel to the west-directed transport direction of the granulitic nappe. Detailed geological studies along this northern margin reveal that the c. 1.0 Ga granulites of the EGMB do not share a direct contact with the Archaean granite-greenstone terrane of Singhbhum, but are actually juxtaposed against a Late Archaean (2.8–2.5 Ga) high grade terrane referred to as the Rengali Province. Structural studies reveal that the EGMB-Rengali Province contact has a WNW-ESE strike with sub-vertical dip, with prominent asymmetric markers indicating dextral strike-slip shearing along a horizontal transport vector. Microstructural studies indicate that fabric formation during strike-slip deformation is controlled by plastic deformation of quartz, while other minerals remained passive or deformed in a brittle manner. Electron Back-Scatter Diffraction (EBSD) studies on selected samples from the contact zone indicate that quartz deformed mostly by prism , rhomb and basal slip, with asymmetry indicating dextral simple shearing. The Rengali Province samples show that earlier shortening (pure shear) microstructures and quartz CPO patterns were also sheared dextrally by this later deformation. These results confirm that the northern boundary of the EGMB is not a thrust, but a strike-slip shear zone that operated well after granulite metamorphism, and at lower temperatures characteristic of the greenschist facies. Shortening structures in the Rengali Province and the Singhbhum Craton are related to an older deformation event unrelated to emplacement of the EGMB. Gravity studies across the contact confirm that the shear zone continues vertically to a depth of at least 25 km. Thus, integrated geological and geophysical studies confirm the strike-slip nature of the craton-mobile belt boundary.

This study focuses on finding the causes for the collapse of Sun temple, Konark, Odisha, India and the disappearance of the ancient Chandrabhaga river using satellite imagery and geophysical data. Gravity and magnetic anomalies near the Sun temple reveal the presence of two sets of faults trending NW–SE and NE–SW. The 3D gravity inversion depth model reveals an uplift-depression structure associated with these faults, which are steeply dipping in the proximity of the Sun temple. Reactivation of these faults is supported by evidences such as shifting of river channels, asymmetric arrangement of ox-bow lakes and combing features along the river bank, changes in the sinuosity index (SI) of the Kushabhadra, Kadua and Patharbuha rivers, all distributaries of the Mahanadi, against these faults. The most notable feature is the truncation of older channels by the present Patharbuha river, which instead of flowing towards the sea, meets the Kadua river to the east; this is interpreted to be linked to the reactivation of the NW–SE fault which results in the extinction of River Chandrabhaga. Remnants of River Chandrabhaga are present near the Sun temple. The timing of sediment deposition due to channel shifting, as well as fluvial morphological changes along the coast are found to be contemporaneous with the building and collapse of the Konark temple.

Fluoride contamination in groundwater is a major problem throughout the world as well as in India. High-fluoride content was reported in the hot springs of Atri and Tarbalo sites in Odisha, India, and residents of nearby villages showed the manifestations of fluorosis. Around 39% of the groundwater samples showed fluoride concentration > 1 mg/l, higher than the desirable limit specified by the WHO. The dominant chemical facies of groundwaters were ions of Ca-Mg-HCO3 and Ca-Na-Cl, which infers the lithological control over the hydrochemistry of this area. A strong correlation between fluoride and other major ions could not be found, suggesting that multiple processes are responsible for the enriched fluoride concentration observed in the study area. The major geochemical processes include dissolution of fluoride-bearing minerals from the rocks, evapotranspiration, agricultural input and mixing of cold groundwater with hot spring water containing high fluoride. The maximum fluoride exposure doses through drinking water from fluoride-contaminated tube wells were estimated to be 0.07 mg/kg/d for infants, 0.125 mg/kg/d for children and 0.06 mg/kg/d for adults, which are higher than the minimum risk level (0.05 mg/kg/d). Exposure doses of fluoride indicate that exposure risk is doubled for children in comparison to infants and adults, which might cause severe dental fluorosis and other ailments. Considering the environmental and hydrological set up of the study area, membrane defluoridation process can be suggested as the best remediation method. Nalgonda technique, dilution of fluoride-rich groundwater and better nutrition containing calcium and vitamin C are other possible options that can be included for early mitigation of fluoride contamination.

In the northeastern part of peninsular India, a triangular domain of the Bastar craton is effectively sandwiched between the Eastern Ghats Mobile Belt (EGMB) in the south and the Rengali Province and Singhbhum craton in the north (Fig.1). Figure 1. Rectangle in map shows the study area The geological evolution of this domain is expected to preserve imprints of the amalgamation history of all three Precambrian terrains. This cratonic domain comprises a variety of quartzofeldspathic gneisses (QFG) such as augen gneiss, granitic/granodioritic gneisses along with some leptynites and garnet-biotite schists, enderbites/ charnockites, mafic granulites and amphibolite dykes and sills. These lithologies (except amphibolite) preserve a record of early granulite facies metamorphism. This early granulite fabric is represented as S

In India, the Eastern Himalaya broadly refers to the region east of Bhutan, and conventionally, Darjeeling and Sikkim are generally included within its domain. This report is a compilation of some of the publications since 2016, made by, or in collaboration with Indian scientists who have discussed various geoscientific aspects of the Eastern Himalaya. From the stand-point of the geological input to tectonic framework, studies dealing with structural, metamorphic and geophysical aspects have been compiled in this report, based on the publications from Darjeeling-Sikkim and Arunachal Himalayas, which are the Indian components of the Eastern Himalaya.

Noctis Landing is a proposed Landing Site/ Exploration Zone for human missions to Mars. This study identifies several mineral and water-related spectral signatures in data from Mars Reconnaissance Orbiter (MRO)’s Compact Reconnaissance Imaging Spectrometer for Mars (CRISM). Introduction: Noctis Landing (NL) is a proposed Landing Site / Exploration Zone for human missions to Mars [1]. It is one of 47 sites proposed to NASA at the agency’s First Landing Site (LS) / Exploration Zone (EZ) Workshop for Human Missions to the Surface of Mars convened in Houston, TX, in October 2015. Understanding the mineralogy and volatiles present at the NL site is important for characterizing its geology, environmental evolution, astrobiological potential, possible resources, and promise for human exploration. In this study, we seek to identify mineral and waterrelated spectral signatures in MRO CRISM data released in NASA’s Planetary Data System (PDS). We consider two nested EZs: the Primary EZ (PEZ), ...

The present study investigates the reasons for the heavy siltation in Chilka Lake which is analysed by satellite imagery, ground survey and geophysical studies. Modified normalized difference water index (MNDWI) and linear spectral unmixing method (LSU) reveal the presence of a wetland, suspended sediments and aquatic weeds along the northeastern boundary of the lake and beyond. Gravity, magnetic data and 3D inversion modelling reveal various sets of faults that were periodically reactivated to form uplifted and subsided blocks around the lake. Geomorphic evidence like low valley width/height ratio (Vf) with <1.5 (valley undercutting due to uplift), low mountain front sinuosity index (Smf), basin asymmetry, transverse topographic symmetry (T), compressed meanders, and flow diversion are all indicative of neotectonic activity and the resulting reactivation of faults. Neotectonic activity is also evidenced from the occurrence of seismic tremors in and around the Chilka region which lies in Zone III of the seismic zonation map of India. This neotectonic activity can be related to the compressional stresses persisting over most parts of the Indian Shield due to the Himalayan Orogeny. The resulting uplift and subsidence led to erosion of the uplifted block and sedimentations in the subsided block by the rivers Daya and Bhargabi. This is the probable cause of heavy siltation in Chilka Lake, where the eroded sediments of the uplifted block are deposited by these two rivers. This work reveals an interconnection between geomorphic features and subsurface structures that together control neotectonic activity in the Chilka region. Compressive stresses related to the Himalayan Orogeny reactivate ancient NW–SE and NE–SW trending faults, resulting in uplift and subsidence of basement blocks. Recent sedimentation is controlled by these basement uplifts and depressions. Uplifts trigger river erosion, transferring large volumes of sediment into the Chilka Lake depression. Organic nutrients transported with the sediments are responsible for the enhanced growth of aquatic weeds in the northeastern part of Chilka Lake. This work reveals an interconnection between geomorphic features and subsurface structures that together control neotectonic activity in the Chilka region. Compressive stresses related to the Himalayan Orogeny reactivate ancient NW–SE and NE–SW trending faults, resulting in uplift and subsidence of basement blocks. Recent sedimentation is controlled by these basement uplifts and depressions. Uplifts trigger river erosion, transferring large volumes of sediment into the Chilka Lake depression. Organic nutrients transported with the sediments are responsible for the enhanced growth of aquatic weeds in the northeastern part of Chilka Lake.

Hydrous fluids play a vital role in the chemical and rheological evolution of ductile, quartz-bearing continental crust, where fluid percolation pathways are controlled by grain boundary domains. In this study, widths of grain boundary domains in seven quartzite samples metamorphosed under varying crustal conditions were investigated using Atomic Force Microscopy (AFM) which allows comparatively easy, high magnification imaging and precise width measurements. It is observed that dynamic recrystallization at higher metamorphic grades is much more efficient at reducing grain boundary widths than at lower temperature conditions. The concept of force-distance spectroscopy, applied to geological samples for the first time, allows qualitative estimation of variations in the strength of grain boundary domains. The strength of grain boundary domains is inferred to be higher in the high grade quartzites, which is supported by Kernel Average Misorientation (KAM) studies using Electron Backsca...

<p>In the fast-growing economies around the world, the demand for energy as well as environmental concerns make geothermal energy a potential renewable energy source. Most geothermal provinces across the world have the capacity to generate enormous amounts of hydrothermal energy, and hot springs in these areas are generally associated with active volcanic or tectonic activity. With modern technical advancement, low enthalpy geothermal systems (< 100°C) are also being considered for geothermal energy production. In non-volcanic hot springs, the water temperature remains low compared to volcanic hot springs. We study two such hot springs located within Neoproterozoic granulites of the tectonically stable Eastern Ghats Belt (EGB) of the Indian shield. The source of heat for these amagmatic hot springs may either be deep-seated fracture zones, or alternative heat sources at shallow crustal levels. A combination of geological, geochemical, hydrological and geophysical techniques has been applied to characterize non-volcanic hot springs in India. The hot springs at Atri and Tarbalo are located to the south of the Mahanadi Shear Zone within the EGB. Penetrative granulite facies planar structural fabrics in rocks of the northern EGB are reoriented within an E-W striking, northerly dipping ductile shear zone that is subsequently dissected by WNW-ESE trending, sub-vertical pseudotachylite-bearing faults and fractures. Tube and dug wells around the shear zone yield both hot (~ 60°C) and cold (~ 28°C) water, sometimes spatially only 20 metres apart. Chemical analyses indicate both have distinct compositions, with hot waters rich in Na<sup>+</sup>, K<sup>+</sup> and Cl<sup>-</sup> while cold-waters have higher Ca<sup>2+</sup> and HCO<sub>3</sub><sup>-</sup> concentration. Stable isotope analyses (δ<sup>2</sup>H and δ<sup>18</sup>O) of both waters indicate that both are meteoric in origin. Tritium (<sup>3</sup>H) and <sup>14</sup>C analyses indicate that hot spring waters are much older than the non-thermal groundwater. The hot water is 17714 years old, while the non-thermal groundwater indicates modern day recharge. This suggests that both waters come from different reservoirs. VLF-electromagnetic studies indicate that water exists in isolated pockets beneath the crystalline country rocks, but also circulated through WNW-ESE trending fracture systems. Heat production studies reveal that the EGB is a high radiation zone, and some host rocks have exceptionally high heat producing element (HPE) concentrations (primarily thorium) within the minerals monazite and thorite. Hence, meteoric water is entrapped in those “perched aquifers” near HPE-rich pockets for a long duration and has sufficient time to undergo radiogenic heating, shielded from the non-thermal groundwater circulating within the fracture system. These isolated pockets act as sources for the hot springs,with HPE being the source of heat. The high HPE distribution in the crust resulting from Neoproterozoic geological events has, thus, elevated the present-day equilibrium geotherm in the EGB, forming sources for shallow-level, non-volcanic hot springs within a tectonically inactive terrane. Therefore, the hot springs in these regions, as well as the hot dry rocks of these areas can be considered as potential geothermal resources.</p>

Noctis Landing is a proposed Landing Site/ Exploration Zone for human missions to Mars. This study identifies several mineral and water-related spectral signatures in data from Mars Reconnaissance Orbiter (MRO)’s Compact Reconnaissance Imaging Spectrometer for Mars (CRISM).