Early Quaternary stress change in Central Asia

The wide boundary zone between stable Asia and South-East Asia affected by the Himalayan orogeny illustrates a large variety of tectonic responses to compressional stresses applied to the Himalayan-Tibet foreland. The present-day stress pattern in Asia is relatively well known thanks to the World Stress Map (WSM) database, but its evolution with time during the late Cainozoic remains poorly studied. We compiled a total of 443 paleostress tensors obtained from the inversion of fault-slip data for the entire Cainozoic period over on a wide region ranging from the Baikal rift and Altai-Sayan belt in the north, to the western Tien Shan, the Tibet Plateau and its surroundings, and the Shanxi rift. We used 191 tensors obtained during field compaigns of the authors and the 252 remaining data were compiled from the literature. In addition, 36 tensors from the inversion of focal mechanism data are taken as reference for the present-day stress field in the Tien Shan, Altai-Sayan and Baikal areas. The compilation shows that the appearance of compressional stresses in Central Asia (Tien Shan, Altai-Sayan and Baikal) and at the northern and eastern margins of the Tibet Plateau started coeval with the onset of extensional stresses and normal faulting inside the Tibet plateau (South Tibet), in the Early Pliocene. At the end of the early Pleistocene, the stress and deformation pattern changed significantly, both in the stress regime and in the orientation of the SHmax directions. This stress change affected most of the Asian plate with increasing intensity towards South Tibet.