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

S. V. Srikantia ¹, P. G. K. Bhat ¹, N. Subramani ¹

Affiliations
1 Geological Survey of India, Bangalore-560 011, IN

Abstract

The paper records the first occurrence of Orbicular rocks from the Closepet Granitoid belt near Hoskote, Tumkur district, Karnataka. The orbicules occur in a dioritic country rock enclosed within grey Closepet Granitoid. These are multishelled orbicules with shells of plagioclase and hornblende with a core of the same minerals. There are also proto-orbicules. The chemical analyses of orbicules fall in mafic tonalite field on K₂O - CaO plots. Individual shells reflect a basic rock parentage. The orbicules are derived from a metabasic enclave due to granitic action by melting, diffusion and concretionary process in hydrous stage.

Keywords

Closepet Granites, Orbicules, Igneous Petrology, Hoskote, Tumkur, Karnataka.

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