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V. Divakara Rao ¹, U. Aswathanarayana ², M. N. Qureshy ¹

Affiliations
1 National Geophysical Research Institute, Hyderabad, IN
2 Centre of Advanced Study in Geology, UniversIty of Saugar, Sagar (M.P.), IN

Abstract

With the object of investigating the mode of origin of the Closepet granite, Mysore state, India, integrated geological, geochemical and geophysical studies have been made of the northern part of the pluton as also the adjacent Chitaldurg and Hosdurga granites and Penmsular gneiss. The Joints (post-emplacement'l) in the Closepet granite and the ratios of mineral pairs indicate that (i) the grey and the pink varieties of the Closepet granite and the Chitaldurg granite are comparable to many respects and might have had a common mode of origin, (ii) the Hosdurga granite is distinguishable from the above granites in having a lower amount of quartz and K-feldspar and higher amounts of plagioclase and mafics and (iii) the Peninsular gneiss markedly differs from the Closepet and Chitaidurg granites, and departs from them in the same direction as the Hosdurga granite but in a more accentuated way. A two-stage model for the origin of the Closepet granite is supported by the following petrological evidence presence of two generations of quartz, unzoned anhedral plagioclase, replacement of plagioclase by microcline and the presence of perthite and myrmekite along With K-feldspar and quartz. The Closepet granite was apparently formed by palingenesis (starting from the Peninsular  gneiss) and metasomatism involving enrichment in Si, K and Na, among other elements.

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M. N. Qureshy ¹, S. C. Bhatia ¹, D. V. Subba Rao ¹

Affiliations
1 National Geophysical Research Institute, Hyderabad, IN

Abstract

The regional gravity survey in the area bounded by Lat. 21°N to 23°N and Long. 85°E to 87°E has brought out a broad gravity' low' over the granite batholith south of the Singhbhum thrust zone. The amplitude of gravity' low' is more in the southern portion (about 30 mgal near Keonjhargarh) than that in the northern portion of the granite batholith (about 20 mgal near Hatgamaria). This gravity 'low' in general suggests that the granite body may continue to a considerable depth.

A broad gravity 'high' has also been observed east of Singhbhum granite where one or two outcrops of basic rocks are observed. The areal distribution of this' high' would seem to suggest the existence of a substantial amount of basic rocks in this area which may represent the Simlipal and the Dhanjori basins filled with high density material as suggested by Iyengar and Alwar.

This correlation of gravity to surface geology can be advantageously used as an aid to structural mapping and in getting the third dimensional configuration of the major rock types.

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M. N. Qureshy ¹, W. E. K. Warsi ²

Affiliations
1 Department of Science & Technology, New Delhi, IN
2 Massachussetts Institute of Technology, US

Abstract

An analysis of gravity data in a strip of 1100 × 303 km² in north Indian shield brings out correlation between geology and gravity. In particular, gravity 'highs' are found to correlate well with a Precambrian sedimentary volcanic pile (Bijawars) which is an important ore carrier in the Indian shield. This correlation of gravity data in conjunction with aeromagnetic data and photogeologic map is suggestive of a significant role of gravity surveys, where extensions of some litho-stratigraphic horizons beneath covers may be sought after as a working hypothesis in a concept oriented mineral exploration programme.

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M. N. Qureshy

Abstract

No Abstract.

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