Decoupling between upper crustal deformation of southern Tibet and underthrusting of Indian lithosphere

More accurate normal fault mapping and more recently constrained extension rates in southern and central Tibet allow to better discuss the mechanical processes responsible for the distribution of extension in Tibet. First, we show that the location of the rifts in southern Tibet south of the Karakorum-Jiali fault zone (KJFZ) does not exactly correspond to that of the rigid Indian lower lithosphere flattening below southern Tibet (underthrusting) inferred by P-waves global tomography, thus suggesting an absence of mechanical coupling between the two processes. Instead, E-W extension south of the KJFZ appears primarily due to divergent, orthogonal thrusting along the curved Himalayan arc, as proposed earlier. North of the KJFZ however, lower amplitude extension, distributed on numerous scattered normal faults in the western Qiangtang terrane, absorbs distributed eastward extrusion, while eastern Qiangtang is extruded more rigidly by the Xianshuihe fault, following a slip-line resulting from in-plane forces due to the collision/indenter, visible as a major discontinuity in the GPS velocity field.