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Geochemistry and geotectonic implication of basic volcanic rocks in the Lower Gondwana sequence (Upper Palaeozoic) of the Sikkim Himalayas

Published online by Cambridge University Press:  01 May 2009

S. Sinha Roy  and
H. Furnes
S. Sinha Roy
Affiliation:
Geological Survey of India, 27, Chowringhee Road, Calcutta 70016, India
H. Furnes
Affiliation:
Geologisk Institutt, Universitetet i Bergen, Avd. A., J. Frielesgt 1, 5014 Bergen, Norway
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Summary

As in Kashmir and Arunachal Pradesh (NEFA) Himalayas, the Upper Palaeozoic (Lower Gondwana) sequence in Sikkim Himalayas contains basic lavas. These are interbedded with boulder bed/pebble slate, sandstone andshale, exposed in a tectonic window. Geochemically the basic lavas are characterized by high contents of TiO2, K2O, P2O5 and ‘incompatible’ trace elements. The chemistryis compatible with a small degree of partial melting under high pressure ofa titan-phlogopite-bearing peridotite mantle. The only primary quench phases are frequent apatite, magnetite and profuse ilmenite, the latter accounting for the high FeO/Fe2O3 ratio of the rock, and demonstrating rapid crystallization. The geochemistry of the lavas appears to be consistent with basic volcanism associated with the initiation of continental rifting. From this study and from a consideration of the geochemistry of the volcanic rocks of similar age in Kashmir area, it is suggested that rifting of the northern continental margin of the Indian plate and formation of a transitional crust during Upper Palaeozoic times are important geotectonic features in the Himalayan region.

Type
Articles
Information
Geological Magazine , Volume 115 , Issue 6 , November 1978 , pp. 427 - 436
Copyright
Copyright © Cambridge University Press 1978

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