Vertical coherence of deformation in lithosphere in the eastern Himalayan syntaxis using GPS, Quaternary fault slip rates, and shear wave splitting data

摘要

We present 59 new SKS/SKKS and combine them with 69 previously published data to infer the mantle deformation field in SE Tibet. The dense set of anisotropy measurements in the eastern Himalayan syntaxis (EHS) are oriented along a NE-SW azimuth and rotate clockwise in the surround regions. We use GPS measurements and geologic data to determine a continuous surface deformation field that is then used to predict shear wave spitting directions at each station. Comparison of splitting observations with predictions yields an average misfit of 11.7 degrees illustrating that deformation is vertically coherent, consistent with previous studies. Within the central EHS in areas directly surrounding the Namche-Barwa metamorphic massif, the average misfit of 11 stations increases to 60.8 degrees, and vertical coherence is no longer present. The complexity of the mantle anisotropy and surface observations argues for local alteration of the strain fields here associated with recent rapid exhumation of the Indian crust.