Lithospheric Density Structure and Effective Elastic Thickness Beneath Himalaya and Tibetan Plateau: Inference From the Integrated Analysis of Gravity, Geoid, and Topographic Data Incorporating Seismic Constraints

摘要

Investigation of deep crustal and lithospheric structures is essential to understand the nature of geodynamical processes beneath the Himalaya and Tibetan plateau of the India-Eurasia collision zone. Our density cross sections across the Himalaya-Eurasia collision zone using integrated 2-D modeling of gravity, topography, and geoid data incorporating constraints from seismic information supports the above contention. Analysis of gravity, geoid, and elevation data over the interior of the Tibetan plateau predicts complete isostatic compensation, whereas margins of the plateau, having large topographic gradients, show lack of isostatic compensation as the Airy Moho differs from flexural Moho and seismic Moho beneath the Himalaya. Our 2-D modeled lithospheric cross sections show thick crust (similar to 75 km) and thick lithosphere (similar to 240 km) beneath the Himalayas and southern Tibetan plateau and relatively thin crust (similar to 60 km) and thin lithosphere (similar to 140 km) beneath the northern Tibetan plateau. Therefore, depth of lithosphereasthenosphere boundary (LAB) mimics the Moho relief. Thinner crust and thin lithosphere under northern Tibetan plateau suggest the importance of the mantle isostasy where the temperature is anomalously high. This corroborates with the presence of recent potassic volcanism, inefficient Sn propagation, east and southeast oriented global positioning system displacements, and large shear wave splitting anisotropy (2 s). Excellent correlation between effective elastic thickness and lithospheric thickness predicts hot and deformable lithosphere in the northern Tibet and underthrusting of cold Indian mantle beneath the Himalayas.