Insight into the nature of Indian crust underthrusting the Himalaya

Abstract

ABSTRACT The nature of the Indian crust underthrusting the Himalaya may be studied in xenoliths within Ordovician granites in the external part of the Himalaya. These peraluminous S‐type granites have travelled for c. 200 km in the Main Central (or related) thrust. The granites and xenoliths sample Indian basement now buried beneath the High Himalayan thrust pile. In low‐strain granites the xenoliths reveal polyphase tectonite fabrics older than the fabrics in the country rocks. Most xenoliths show greenschist/lower amphibolite facies assemblages; none is typical granulite facies of the Indian Shield. Therefore, the portion of the Indian crust underthrusting the Himalaya may be early/middle Proterozoic reworked Indian Shield, as in peninsular India. Alternatively reworking may be assigned to the Pan‐African (late Proterozoic) orogeny. This prospect is raised by recent work in East Antarctica but evidence in the Himalaya is rather ambiguous. If confirmed, a Pan‐African event calls for reassessment of the geological history of the Himalayan region, particularly with respect to the placing of India in Gondwanaland.