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Structural evidence supporting a remnant origin of patchy charnockites in the Chilka Lake area, India

Published online by Cambridge University Press:  01 May 2009

S. Bhattacharya ,
S. K. Sen  and
A. Acharyya
S. Bhattacharya
Affiliation:
Department of Geological Sciences, Jadavpur University, Calcutta-700 032, India
S. K. Sen
Affiliation:
Department of Geological Sciences, Jadavpur University, Calcutta-700 032, India
A. Acharyya
Affiliation:
Department of Geological Sciences, Jadavpur University, Calcutta-700 032, India
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Abstract

Dark patches of charnockitic rocks characterized by orthopyroxene occur within garnetiferous granite gneisses (leptynites) in a granulite-migmatite suite around the Chilka Lake, Orissa, within the Eastern Ghats belt in the Indian Precambrian. Analysis of structures of different scales observed in this terrain establishes the presence of three phases of deformation. S1 is pervasive in the metapelitic granulites (mainlykhondalite), while in the migmatite complex composed of leptynites, charnockites and quartzofeldspathic veins, S1 is present exclusively within the charnockite lenses and bands, and shows different stages of obliteration in the associated leptynites. Thus, the charnockite patches must be earlier than the surrounding migmatitic rocks. The charnockite patches and the surrounding leptynitic gneisses are chemically quite different and the two rock types are not related by any prograde or retrograde transformation. The shapes and disposition of charnockite patches in the mixed exposures are found to be largely controlled by the third phase of folding and locally associated shearing. The kinematics of this late deformation are not favourable for fluid ingress from deeper levels.

Type
Articles
Information
Geological Magazine , Volume 130 , Issue 3 , May 1993 , pp. 363 - 368
Copyright
Copyright © Cambridge University Press 1993

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