Indian plate segmentation along the Himalayan arc: A multi-proxy approach

Abstract

The underthrusting Indian plate beneath the Himalaya is considered to be segmented along its arc which is manifested in terms of variations in the angle of underthrusting of the Indian mantle lithosphere (IML) and its northern limit beneath Tibet. The pre-existing transverse ridges in the Ganga foreland basin have also been related to these segmentation boundaries. These segmentations imply a change in the mechanical properties of adjoining blocks which should manifest in the form of spatial variations in the topography build-up and other related parameters. We have analyzed the normalized river channel steepness index (k_sn) for the entire Himalaya in conjunction with the northern extent of the IML, width of the Ganga foreland basin, and Bouguer gravity anomaly of the orogen to identify its possible correlation with the lithospheric segments and their boundaries. The results reveal spatial variability in the k_sn along the arc linked to the segmentation of the Indian plate. The study suggests six distinct sectors in the Himalaya, similar to the ones delineated based on correlation between the width of the Ganga foreland basin and disposition of major Himalayan thrusts. Major offsets in the pockets of the high k_sn from the arc-parallel distribution are related to the transverse tectonic fabric of the Indian plate in the Ganga-Brahmaputra plains. Integration of these results support mechanically strong Indian lithosphere for the Kashmir-Himachal sector and the eastern part of the Arunachal sector and weakest lithosphere for the central-eastern Nepal sector.