Late Cenozoic tectonic stress fields of the Mongolian microplate

Abstract

The article deals with the Late Cenozoic fault tectonics and crustal stress state in the Mongolian block (Central and West Mongolia). An analysis was made of the stress field reconstructions, tectonic deformations in active fault zones of the central part of the block (Khangai dome), adjacent uplifts, and intermountain basins, i.e., Mongolian Altai, Gobi Altai, Valley of Lakes, and Khan-Taishir-Nuruu, Khan-Khukhei and Bolnai uplifts. Deformations associated with a general northeast-trending collision compression are concentrated along the periphery of the Mongolian block, the maximum compression occurring on the western and southern block boundaries and giving rise to the right- and left-lateral transpressive structures of Mongolian and Gobi Altai. The deformations associated with the contraction of the Earth's crust affect not only bordering ranges but also the intermountain depressions separating the Gobi and Mongolian Altai from the Khangai and the southern Khangai domes. A variety of deformations in the central Khangai dome is associated with the interaction between extension occurring under dynamic influence of the mantle anomaly and regional north-east compression. Tectonic stiffness of the Khangai block appears to be somewhat favorable to the deformation transfer to its northern termination, i.e., the North Khangai strike-slip fault. This latitudinal zone shows that the compression increases toward the west where it merges with the transpressive structures of the Mongolian Altai, whereas the extension increases toward the east. The formation of releasing bend strike-slip features may be due to the proximity of the Baikal rift zone that resulted from north-west extension associated to a general southwestward movement of the Amur plate.