Flexure of the India plate underneath the Bhutan Himalaya

Abstract

We investigate flexural geometry and rheology of the India plate beneath the eastern Himalaya from a new gravity data set acquired in Bhutan. Compared to the well-studied Nepal Himalaya, the obtained Bouguer anomaly profiles across the range show shorter wavelength flexure of the lithosphere with a narrower and shallower foreland basin. This new data set and seismic Moho constraints are interpreted together in terms of lithospheric flexure using a 2-D thermomechanical model. Our results suggest that the strongest layer of the continental lithosphere beneath Bhutan is the upper mantle, as it is beneath Nepal. The observed west-to-east decrease in flexural wavelength is associated with weakening mantle rheology. The simulations show that this decrease can be related to ductile mantle behavior: either hydrated wet dunite or dry and hot olivine rheology. Both models display decoupled lithospheric layers leading to an eastward decrease of flexural rigidity from ∼1024 to ∼5·1022 N m in Nepal and Bhutan, respectively. Key Points Flexure and rheology of the India Plate in the Eastern Himalayas is investigated New gravity dataset constrains comprehensive 2D thermo-mechanical modeling Flexural rigidity decreases both across and along (W to E) the range. © 2013. American Geophysical Union. All Rights Reserved.