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

S. K. Sen ¹, S. Ray ¹, D. Dasgupta ¹

Affiliations
1 Department of Geology and Geophysics, Indian Institute of Technology, Kharagpur, IN

Abstract

In the type area of the charnockites, south of the city of Madras, foliation attitudes of marker horizons of leptynites and of basic granulite bands trace a map pattern characterized by four-fold hinges. The overall structure of the area is brought out by the swerve of axial planes of these folds from NNE in south-west through E-W in the central part to N-S in southern part in a broad sweep. The folding is noncylindrical; and a probable structural interpretation, as advanced here, envisages a series of tight isoclinal folds on which a folding around a N-S axial plane has been superposed.

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D. S. Bhattacharyya ¹, D. Dasgupta ¹

Affiliations
1 Indian Institute of Technology, Kharagpur, IN

Abstract

No Abstract.

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D. S. Bhattacharyya ¹, D. Dasgupta ¹

Affiliations
1 Department of Geology and Geophysics, Indian Institute of Technology, Kharagpur 721 302, IN

Abstract

The Precambrian Dalma metabasalts stretching for more than 200km represent original oceanic tholeiites. The metabasalts can be represented by eleven different groups of mineralogical assemblages ranging from low greenschist to high amphibolite facies. Spatial distribution of these six groups indicates increasing P-T conditions from east to west.

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P. Sanyal ¹, D. S. Bhattacharyya ¹, D. Dasgupta ¹

Affiliations
1 Department of Geology and Geophysics, IIT, Kharagpur, IN

Abstract

The Arkasani granite gneiss occurs as detached elongate outcrops close to the northern margin of the Chakradharpur granite gneiss. Both show imprints of the same deformation and same textural and structural characters. While the Chakradharpur gneiss ranges from tonalite - granodiorite - granite - alkali feldspar granite, the Arkasani gneiss is an alkali feldspar granite. Major element compositions of the two are either gradational or overlapping. The former has higher Na₂O values and the latter higher K₂O values. The two groups of gneisses are genetically related.

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S. S. Bhat ¹, A. Bhattacharya ², H. C. Dasgupta ², D. Dasgupta ²

Affiliations
1 Geological Cell, GM Ofice, Barkakana Area, PO: NTS Barkakana-829103, Bihar, IN
2 Geology and Geophysics Department, IIT, Kharagpur-721302, IN

Abstract

Petrology and mineral chemistry of garnetiferrous chlorite schists belonging to Deogiri formation in the Sandur schist belt have been studied. Mineral assemblages and chemical data on muscovite, biotite, chlorite, garnet from the Deogiri chlorite schists indicate low grade regional metamorphism under greenschist facies condition. Mineralogy of the metabasics associated with Deogiri chlorite schists and with the overlying Donimalai formation in this region, except near the peripheral contacts, also suggest greenschist facies metamorphism for the schist belt. Mineralogy and chemistry of Deogiri metabasalts indicated ocean floor type of alteration/metamorphisrn for the Deogiri metabasalts. Rocks close to the granite contact have seemingly undergone an episode of thermal metamorphism which is distinct from the regional metamorphism of the entire schist belt and possibly isolated both in space and time.

Keywords

Mineral Chemistry, Metamorphism, Sandur Schist Belt, Karnataka.

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