Late Cenozoic fields of the tectonic stresses in Western and Central Mongolia

Abstract

The paper addresses the Late Cenozoic fault tectonics and the stress state of the Earth’s crust within the Mongolian microplate, embracing Central and Western Mongolia. We analyze the results of reconstructing the stress fields and the tectonic deformations in the zones of active faulting, located at the uplands and in the intermountain trenches, which bound the microplate (Mongolian Altai; Gobi Altai; Dolinoozersk trough; Khan-Taishir-Nuruu, Khan-Houkhei, and Bolnai uplands) and the Khangai dome. Deformations related with the northeastern general-scale collisional compression are concentrated along the periphery of the Mongolian microplate, and the maximum compression is focused on its western and southern boundaries, thus forming the right- and the left-lateral transpressive structures of the Mongolian and Gobi Altai. The deformations associated with the shortening of the Earth’s crust involve not only the mountain ridges framing the block, but also the intermountain troughs that separate the Gobi and Mongolian Altai from the Khangai dome, and the southern portion of the Khangai Uplift. The diversity in the deformations within the central Khengai region ensues from the coupling of tension caused by the dynamical impact of the mantle anomaly, which is located east of 100°E, with a regional NE compression. Owing to the relatively rigid Khangai block, the deformations are transferred to the northern bound of this structure, namely the seismically active North Khangai fault. The role of compression increases to the west of the zone, where it conjugates with the transpressive structures of the Mongolian Altai. The tension becomes more important in the western part of this zone where the releasing bends are formed. A region characterized by extra tension is localized also to the east of 100° E. In terms of the gradient in the lithosphere thickness and the structure types of the upper crust, the submeridional line running along 100°E is interpreted as the key interblock boundary.