Indian Gondwana Plate margin and its evolutionary history

Abstract

The outline of Indian Plate in the Gondwanaland Plate mosaic has been reconstructed. The basic premise for the reconstruction lies in the identification of the suture zone along Indus-Yarlung tectonic zone and Indo-Burman range, both of which are wreathed with ophiolite complexes. The north eastern margin of the Indian part of the Gondwana Plate, which was ill-defined in many earlier reconstructions, is now more precisely delineated with the find of slide-generated olistostrom bodies representing plate marginal trench setting around Ukhrul-Paoyi-Kiphire area of the ophiolite belt of Manipur-Nagaland. The recent report of continental Gondwanas close to this suture zone lends credence to this palaeogeographic reconstruction. On the north, the continental sediments having distinct Gondwana entity rarely extend to the Tethyan basin and as such the Indus-Yarlung Suture truly delimits the Gondwana Plate domain. The Himalayan front is regarded as Tethys-facing margin of the Gondwana continent. Along the eastern margin of Indian Plate, rifting as a sequel to ocean floor spreading led to the evolution of coastal troughs of Cauvery, Palar, Godavari-Krishna and Athgarh which bears records of marine transgressions during Aptian-Albian time from a juvenile Indian Ocean. These oceanward tilted troughs may represents the rifted arm of a triple junction formed during the continental fragmentation. The discovery of such troughs in the Upper Assam and Bengal Basin suggests that the separation of India from Eastern Gondwanaland occurred in a NE-SW direction. The Cambay and the Kutch basins document similar evolutionary history along the western margin of the Indian Plate. As a consequence of crustal tension accompanying the fragmentation, the outpour of tholeiitic basalt took place in Rajmahal, Khasi-Garo-Mikir Hills and Upper Assam at 100-105 million years along the west coast. The earliest manifestation of volcanism has been recorded in Saurashtra which is considered to be contemporaneous with Rajmahal volcanicity. It is suggested that both the eastern and western margins of the Indian Gondwana Plate bear closely related records of fragmentation in the Early Cretaceous time.