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

V. Rajamani ¹, E. J. Krogstad ², G. N. Hanson ², S. Balakrishnan ¹

Affiliations
1 School of Environmental Sciences, Jawaharlal Nehru University, New Delhi 110067, IN
2 Department of Earth and Space Sciences, Slate University of New York, Stony Brook, New York 11794, US

Abstract

Structural and geochemical evidence including major and trace elements, and Pb-isotopic data on K-feldspars, froin the granitoid rocks adjoining the Kolar Schist Belt are presented to show (1) that the Patna Granite an the NW of the belt is dissimilar to any granitoid rock E of the belt and (2) that the main granitoid gneiss immediately E of the belt, the Karnbha Gneiss, is nearly identical to the Bisanattam Granite of Narayanaswamy er al (1960).

Full Text

     

V. Rajamani ¹, K. Shivkumar ¹, G. N. Hanson ², J. W. Granath ²

Affiliations
1 School of Environmental Sciences, Jawaharlal Nehru University, New Delhi 110067, IN
2 Department of Earth and Space Sciences, State University of New York at Stony Brook, New York 11794, US

Abstract

The amphibolites in the Kolar schist belt include four textural types, schistoic, granular, massive and fibrous and occur in abundance in that order. The fibrous variety consists of two coexisting calcic amphiboles (A1 rich hornblende and A1 poor actinolite). The other three varieties contain hornblende and plagioclase (An₄₀ to An₈₅). The texture, mineralogy and mineral chemistry suggest metamorphism in the middle to upper amphibolite facies.

Major and Rare earth elements (REE) data indicate that (a) the fibrous amphibolite is somewhat similar to high-Mg basalts of Archean greenstone belts but with a strongly, heavy REE depleted pattern, (b) the other three varieties are similar to low-K oceanic tholeiites with slightly light REE depleted patterns and with strong positive Eu anomalies, and (c) the two groups do not represent primary melt compositions generated by the partial melting of a pyrolite mantle. It is concluded that the Kolar amphibolites must have been evolved from at least two separate parent magmas generated from different temperature and pressure (depth) conditions.

Full Text