Abstract
Himalayan-Tibetan orogeny has considered as a natural black box in the context of geodynamic evolution and tectonic complexity. The eastward extrusion model of Tibetan crust contradicts with the oblique convergence model in the NE-Himalaya (Bhutan/Arunachal region), where the overall convergence rate accommodated in the Himalaya is about 20–25% less than that in the neighbouring central Himalaya and Eastern Himalayan syntaxis (EHS). We propose that instead of partitioning in the backarc, the NE-Himalaya has developed an active sliver along the Assam-Brahmaputra valley in the outer deformation front, in order to accommodate the deficiency in long-term plate convergence between Himalaya and southern Tibet. We argue that the strong eastward extrusion of Tibetan crust along NE-Himalaya is the main driving force for the unusual development of the Assam-Brahmaputra sliver. This new hypothesis can explain active convergence along EHS, low convergence and subdued topography in Bhutan and Arunachal Himalaya, kinematic and space-problem of Indo-Burmese wedge, and finally solves the contradiction between Tibetan extrusion and oblique convergence model of the HimalayanTibetan orogeny.
Highlights
The dynamic topography of the Earth’s surface, those along continental margins, has been linked to mantle processes in recent studies[1,2]
The oblique convergence model which describes the deformation between Himalaya and southern Tibet along the frontal-arc[8], and the lateral extrusion model which mainly considers deformation of Tibet[8], appear to be mutually contradictory in view of the tectonics and distributed deformation in the NE-Himalaya[8]
It has been proposed that in the NW-Himalaya, the motion between India and southern Tibet is oblique with respect to the structural trend, which is partitioned between right-lateral strike-slip motion on the Karakorum fault system in the back arc, and slightly oblique motion in the Kashmir Himalaya in the frontal arc, leading to the formation of the NW-Himalayan sliver[10]
Summary
The dynamic topography of the Earth’s surface, those along continental margins, has been linked to mantle processes in recent studies[1,2]. Geomorphic offsets, geodetic estimates and the available earthquake data do not support the presence of any active left-lateral fault system in the region[13] This raises question on applicability of the oblique convergence model in the NE-Himalaya. We address this issue and propose that instead of partitioning in the back arc, an active sliver in NE Himalaya has developed along the Assam-Brahmaputra valley in the outer deformation front which is accommodating the oblique motion through distributed deformation. Based on the GPS observations, we address the oblique convergence and outer deformation-front strain partitioning process along the Assam-Brahmaputra valley adjacent to NE-Himalaya
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