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

C. Bhattacharyya ¹

Affiliations
1 Department of Geology, University of Calcutta, IN

Abstract

No Abstract.

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C. Bhattacharyya ¹

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

Abstract

Petrography, mineralogy and chemistry of leptynites and garnetiferous granitegneisses of Garbham area have been described. On the basis of texture, structure and mineral assemblage, the leptynites have been classified mainly into three types A, B and C, all of which have been formed by the granulite-facies metamorphism of sediments of appropriate compositions. A fourth type of leptynite has been shown to have formed by migmatisation of khondalite; with increasing migmatisation-granitisation, this is locally converted into one-feldspar (Kvfeklspar) garnetiferous granite-gneiss. One-feldspar garnetiferous granite-gneiss has been locally formed by the granitisation of khondalite and quartzite. Two-feldspar garnetiferous granite-gneisses are predominant and have evolved by the granulite-facies metamorphism of sediments, possibly shale and/or greywackes, followed by granitisation in the form of K-feldspathisation. Two-feldspar garnetiferous granite-gneisses are suggested to be essentially the variants of acid charnockites. Both the acid charnockites and garnetiferous granite-gneisses suffered K-feldspathisation, the latter having been also locally derived by K-feldspathisat ion of acid charnockite.

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C. Bhattacharyya ¹

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

Abstract

Calc-granulites of Chinnabantupalli area, Srikakulam district were subjected to contact metasomatism by the injection of K-feldspar-forming fluid. This paper describes the mineralogy of the calc-silicate skarns, mineral chemistry of clinopyroxene and garnet, and emphasizes the textural aspects which have a bearing on the genesis of skarn minerals. The minerals like wollastonite, hornblende, biotite, epidote-clinozoisite-zoisite, a part of the scapolites, garnets and calcites were secondarily formed as a result of contact metasomatism. Most of the scapolites are suggested to be of regional metamorphic origin. The formation of wollastonite, other conditions remaining same, is shown to have been favoured by higher CaO/(FeO+MgO) ratio of these rocks.

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B. Goswami ¹, C. Bhattacharyya ²

Affiliations
1 J.K College, Puruliya-723101, IN
2 Department of Geology, Calcutta University, 35 Ballygunge Circular Road, Kolkata-700019, IN

Abstract

Two contiguous, but spatially separated occurrences of nepheline syenites in the northeastern part of Puruliya district, one having biotite as the principal mafic component and the other having amphibole with subordinate biotite as mafic minerals are studied. Although modal mineralogy of nepheline syenites of these two bodies contrasts considerably, bulk chemical compositions of them remain almost same. Petrographic features give evidences of metamorphism. It is Inferred that regional metamorphism of biotite-bearing nepheline syenite under granulite facies condition caused the appearance of amphibole-Bearing nepheline syenite. During this metamorphic transition, possible reactions between minerals are also drawn.

Keywords

Nepheline Syenite, Chhotanagpur Granite Gneiss Complex, Metamorphism, Puruliya District.

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Aditi Das ¹, C. Bhattacharyya ¹

Affiliations
1 Department of Geology, University of Calcutta, 35 Ballygunge Circular Road, Kolkata - 700 019, IN

Abstract

The roughly E-W trending North Puruliya Shear Zone is characterised by generally E-W striking deformed and brecciated porphyritic granitoid gneisses, in places, along with brecciated and limonitised quartzite, aegirine-riebeckite granite gneiss and few small occurrences of apatite-magnetite rock, REE and U-Th-rich barite-bearing small pegmatites, and small bodies of alkali feldspar salite granitelsyenite and poorly exposed carbonatite at one place. The occurrence, field relation, petrography and geochemistry of the carbonatite, apatite-magnetite rock, pegmatites enriched in REE, U-Th, and barite etc. and the alkaline granitoids along the North Puruliya Shear Zone, all taken together suggest possible genetic link of the alkaline granitoids with a carbonated silicate magma emplaced at depth along the rift zone.

Keywords

Alkaline granitoid, Shear Zone, Apatite-Magnetite rock, Puruliya District, West Bengal.

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C. Bhattacharyya ¹, S. Das ¹, J. Banerjee ¹, S. P. Pal ¹

Affiliations
1 Department of Geology, University of Calcutta, 35, Ballygunge Circular Road, Kolkata - 700 019, IN

Abstract

A detailed investigation of the 'rock melt extrusion', reported about three years back in this journal from Puruliya district, suggests it to be a surface phenomenon. The heat generated by burning of the torn out overhead 11 KV electric lines melted locally the fragmentary amphibolite pieces as well as the enclosing deep brown soil to the south of Jabjabigora. Petrographic, physical and geochemicaI data suggest that both the deep brown soil and amphibolite fragments underwent possibly complete melting on the surface, the former at a temperature a little above 1100°C and the latter at above 1350° to 1360°C.

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C. Bhattacharyya ¹, U. Tickha ¹

Affiliations
1 Department of Geology, University of Calcutta, 35, Ballygunge Circular Road, Kolkata - 700019, IN

Abstract

No Abstract.

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