Journal of Geological Society of India (Online archive from Vol 1 to Vol 78)

S. K. Bhushan ¹, V. K. Chittora ¹

Affiliations
1 Geological Survey of India, WR, Jaipur - 302 004, IN

Abstract

Neoproterozoic Malani bimodal volcanism occurs in a cauldron subsidence structure of a shield volcano at Siwana. This collapse caldera has exposed 45 volcanic flows comprising six of basalt, 20 of rhyolite, alkali rhyolite and rhyodacite, 15 of trachyte, one of dacite and three of trachyandesite, composition. Major and trace element geochemistry of lavas shows a bimodal character in the mafic and felsic components. The lower felsic flows are alkaline and highly enriched in HFS elements while the upper flows are peraluminous in composition. Alkalinity has been reintroduced in the uppermost flows. Wide variation in incompatible trace element ratios indicates a nonfractional crystallization relationship between the mafic and felsic magma. Malani volcanism was triggered in an extensional tectonic setting where geotherm was raised by the repeated influx of basaltic magma. Crustal extension inhibited the bouyant rise of silicic magma.

Keywords

Petrology, Bimodal Volcanism, Cauldron Subsidence, Shield Volcano, Geochemistry, Malani Volcanism, Rajasthan.

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P. K. Maithy ¹, C. M. Bindal ², S. K. Bhushan ³, Subodh Sharma ⁴, D. C. Banerji ⁵, Gopendra Kumar ⁶

Affiliations
1 F2212, Rajajipuram, Lucknow, IN
2 Geological Survey of India Lucknow, IN
3 Geological Survey of India Kolkota
4 Geological Survey of India Nagpur, IN
5 Geological Survey of India Jabalpur, IN
6 Geological Survey of India 48 Pandariba, Lucknow - 226 004, IN

Abstract

Lower Gondwana plant fossils from the Bharell Formation, exposed between Plnjoll Nala and Sessa along the Bhalukpong - Bomdila Road, West Kameng district Arunachal Pradesh, are described and reviewed The assemblage comprises Gangarnopteris cyclopterozdes, G intermedia, Glossopteris angustifolra, G communls, G damudIca, G indica, G lntennlttens, Scutum cf stowanum, Vertebrarra indica, Noeggerathiopsis sp , Cherrophyllum lacerata, stem of Buriadia, Cordaicarpus cordal, Rotundocarpus strlatus and Walzkalia cahenu The assemblage is comparable to that of the Karharbari Formation of Early Permian Coalfields of Peninsular India.

Keywords

Plant Fossils, Karharbari, Early Perimian, Arunachal Hlmalaya.

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S. K. Bhushan ¹, V. K. Chittora ¹

Affiliations
1 Geological Survey of India, Jaipur - 302 004, IN

Abstract

Two granitoid bodies each from Palaeo-, Meso- and Neo-Proterozoic periods have been studied for their chemical, petrological and source characteristics. The Proterozoic granitoids are megacrystic as well non-Megacrystic with variable effect by tectonometamorphic events. The Palaeo-Proterozoic granitoids are peraluminous, corundum normative with high proportion of biotite in their modal composition. They contain either orthoclase/Sanidine or andesine as feldspars and iron rich biotite. The Meso-Proterozoic granitoids have high silica with meta-to peraluminous composition. The feldspar chemistry indicates albite/Oligoclase composition whereas they exhibit high iron rich biotite and some being lepidomelane in composition. The Neo-Proterozoic granitoids are invariably porphyntic having higher silica content (>72 wt%), as compared to other granitoids and exhibit strong peraluminous affinity. The feldspar geothermometry indicate 1050°C for Palaeo-, 900-950°C for Meso- and 750°C for Neo-Proterozoic granitoids. The Proterozoic granitoids are orogenic, the degree of deformation varies from pristine, non-Foliated to gneissic and augen gneissic, mostly 'S' type, indicating a sedimentary source material for their generation. The biotite discriminant diagrams also support 'S' type collisional tectontic setting. The garnet-Biotite geothermometery for Palaeo-Proterozoic granitoids where these minerals co-Exist suggest equilibrium temperature of -540°C at 1 or 2 kb pressures. There is appreciable replacement in magnetites of Palaeo-Proterozoic granitoids by K₂O, SiO₂, Al₂O₃ and negligible in Meso- and Neo-Proterozoic rocks. There is gradual increase in SiO₂ and DI from Paleo- to Neo-Proterozoic granitoids. The basement complex, after attaining rigidity and cratonisation by the end Archaean igneous activity was rifted periodically during the Proterozoic times. Extensional events led to the formation of mafic dyke swarms, plutonic and volcanic activity and sedimentary platform covers. However, the aborted rifts were further effected by compressive tectonics giving rise to syn and late tectonic deformational signatures to the intrusive phases and their host rocks.

Keywords

Proterozoic Granitoids, Petrography, Modal Analysis, Geochemistry, Mineral Chemistry, Geothermometry, Rajasthan.

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S. K. Bhushan ¹

Affiliations
1 International Division Geological Survey of India 27, Jawaharlal Nehru Road, Kolkata - 700 016, IN

Abstract

No Abstract.

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S. K. Bhushan ¹

Affiliations
1 Geological Survey of India, 15-16, Institutional Area, Jhalana Doongri, Jaipur - 302 004, IN

Abstract

No Abstract.

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S. K. Bhushan ¹, Priyadarshi Sahoo ²

Affiliations
1 MSPL Limited, Baldota Enclave, Abheraj Baldota Road, Hospet – 583 203, IN
2 Geological Survey of India, Southern Region, Bandlaguda, Hyderabad - 500068, IN

Abstract

The sediments from three stratigraphic levels in the Bababudan schist belt of Dharwar craton exhibit great diversity in major, trace and rare earth element (REE) geochemistry and thus interpreted to represent significant compositional variation in the source rocks. Detailed geological and geochemical studies have been carried out on clastic rocks constituting the Archaean Sargur supracrustals and the Bababudan belt of Dharwar craton (DC), southern India for understanding the geochemical characteristics and to define the Archaean-Proterozoic Boundary (APB/QPC) in southern India. There is significant contrast in the geochemical signatures for the sediments from these stratigraphic levles. The Sargur enclave population is characterised by slight LREE enrichment with (La/Sm)_N ranging from 1.45 to 3.58, almost flat HREE with (Gd/Yb)_N ranging from 0.65 to 1.29 with Eu/Eu* ranging from 0.49 to 0.91 suggesting mafic-ultramafic source rocks in the provenance. On the other hand, the Post QPC (PQPC) rocks are characterised by LREE enrichment with (La/Sm)_N ranging from 2.66 to 7.07, nearly flat HREE with (Gd/Yb)_N ranging from 0.58 to 0.95 and significant depletion of Eu with Eu/Eu* ranging from 0.34 to 0.85, indicating felsic province in the source area. The conglomerates and quartzites representing the QPC are showing mixed nature of these, reflecting the transitional character in depositional environment. Increase in abundance of REE, K₂O/Na₂O, Th/Sc, La/Sc, Th/U, Hf/Ta and Zr/Y ratios are characteristic of the QPC. The PQPC sediments are enriched in Th, U and HFSE like Hf, Nb, Zr and Y, and depleted in Co and Eu than their older counterparts. These geochemical signatures signify the dominance of mafic-ultramafic rocks in the source area for Sargur rocks and the existence of granite-granodiorite for PQPC clastics. Thus, the unconformity related oligomictic quartz pebble conglomerates (QPC) and quartzites at the base of Bababudan Group resembling the QPC of Witswaterand, South Africa signifies that a stable continental crust had already developed in southern India prior to ∼3.0Ga.

Keywords

Geochemistry, Archaean-Proterozoic Boundary, QPC, Bababudan Belt, Clastic Sediments, Dharwar Craton.

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S. K. Bhushan ¹, K. N. Rao ², K. T. Vidyadharan ³

Affiliations
1 MSPL Limited, Baldota Enclave, Abheraj Baldota Road, Hospet – 583 203, IN
2 F-2, Sree Essen Residency, 186/3 RT Vijay Nagar Colony, Hyderabad, IN
3 310/Block-B, Maharaja Residency, Mangalore, IN

Abstract

The present paper documents the petrography, mineral chemistry and petrochemistry of the acid volcanics of St.Mary group of islands. These are essentially characterized by pyroxene bearing rhyolites with average 73.49 wt.% SiO₂. All the rhyolites from these islands are acmite normative, hence peralkaline with phenocrysts of zoned plagioclase and sometimes hypersthene/augite. There is depletion of LREE with moderate negative Eu anomaly. The enhancement of HFSE elements indicates their compatibility with continental crust. These rhyolites have high equilibrium temperature (915°C) at relatively lower oxygen fugacity (10^-16). The acidic lava flows are anorogenic, within plate rhyolites, generated during northern migration of Indian plate over Marion hotspot.

Keywords

Acid Volcanics, Petrography, Geochemistry, St. Mary Islands, Karnataka.

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S. K. Bhushan ¹

Affiliations
1 94134, Mansarovar, Jaipur, 302020, IN

Abstract

No Abstract.

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S. K. Bhushan ¹

Affiliations
1 RMML, Hospet - 583203, IN

Abstract

Due to their unique magnetic, fluorescent and chemical properties, REE are used in science innovations. REE are key components in many technological devices, like hybrid rechargeable batteries, catalysts, glass, polishing, magnets, lasers, TV colour components, superconductors, ceramics etc. They are of great demand for hybrid cars, CD, cameras and high end defense systems. China is the largest producer (>97% of export of world) and has currently >50% of total global resource of REO (Rare Earth Oxides). Whereas USA has 11.8% and India 2.8% resource (mostly from beach sands). Apart from China, Lynas Corporation Ltd. has REE deposit at Mt. Weld, Western Australia and Molycorp at Mountain Pass, California, USA, in advance stage of production. It is in this context that the rest of world minus China organized the conference.

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