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

D. Mukhopadhyay ¹, S. Bhattacharya ¹

Affiliations
1 Department of Geology, Presidency College, Calcutta, IN

Abstract

The deformed pebbles in the conglomerate show a large variation in the orientation of their longest axes as well as in the values of the axial ratios a' and b'. This has been interpreted as due to a nonspherical nature of the original pebbles. The effect of deformation has been separated from the effect of the original shape. It has been shown that a superficial analysis of the shape of deformed pebbles may give a wrong idea about the state of strain in the rocks, and the method by which the true amount of strain can be computed from dc:formed pebbles has been discussed.

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Utpal Bose ¹, A. K. Mathur ¹, K. C. Sahoo ², S. Bhattacharya ¹, Krishan Dutt ¹, V. Aneel Kumar ³, S. S. Sarkar ¹, S. Chowdhury ¹, I. Chowdhury ¹

Affiliations
1 Geological Survey of India, Jhalana Dungri, Jaipur - 302 004, IN
2 Geological Survey of India, Bhubaneswar - 751 012, IN
3 Geological Survey of India, Hyderabad - 500 660, IN

Abstract

The oldest cratonic nucleus pf the Western Indian shield, familiarly known as the Banded Gneissic Complex (BGC), occupies a large tract in the Mcwar plains of South Rajasthan. It has essentially an old gneissic component (3.3 Ga) and a host of mafic bodies associated with detrital and chemogenic sediments which have been subjected to multiple phases of anatexis and granite intrusions (2.9 Ga and later events). The emplacement of Berach granite and succeeding dolerite dyke swarms mark the end-Archaean cratonization process. This also initiated intracratonic and cratonmarginal basin formation.

Later magmatism, especially along the basement-cover interface. is due to local remobilisation of the basement at the time of Proterozoic orogeny.

Keywords

Banded Gneissic Complex, Stratigraphy, Petrochemistry, Rajasthan.

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Rajib Kar ¹, S. Bhattacharya ²

Affiliations
1 Department of Geology J K College, Puruha - 723 101, IN
2 Geological Studies Unit, Indian Statistical Institute 203 B T Road Kolkata 700035, IN

Abstract

Two types of high Mg-Al sapphirie granulites are noted from the area In and around Paderu, Eastern Ghats GranulIte belt, IndIa One is relatIvely more mafic, coarse gramed variety with crude internal foliation (type I) and the other is relatively fine grained, more fe/SiC and migmatitic variety wIth a promment foliation (type II) In thIs granulte belt Impress of three phases of folding could be detected, with corresponding fabric development Enclaves of type I varIety are preserved with in charnockite In the low stram zone core of mesoscopic F₂ folds, defined by S₁, streaky gneissIc fohation The crude mternal foItatIon m the enclave, dIscordant to S₁ of the host could be pre S₁ The bands of type II vanety together wIth mternal foItation, S₂ define F₂ folds Thus the high Mg Al sapphirine granulites preserve the Imprints of the early deformational fabric The mineral growth in them along with this fabric, indicating ultra high temperature metamorphism is correlatable to this early compressive deformation.

Keywords

Sapphirine Granulites, Deformation Structures, Fabric, Mineral Growth, Paderu, Eastern Ghats.

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