Active Tectonics of Central Asia

Central Asia exceeds neighboring territories in the intensity of Quaternary uplifts and active faulting. The active fault kinematics differ in the northeast of the region, from Middle Tibet to Eastern Sayan, and its southern and western parts, including the Himalayas, the Pamir–Punjab syntaxis, and the region north of Gorny and Mongolian Altai. The northeast is dominated by latitudinal left-lateral strike-slips, while the south and west, by right-lateral strike-slips and northwest- and latitudinally striking overthrusts. The features of active tectonics are governed by the upper mantle structure, studied in three horizontal sections. The highest mountain systems, with sharply reduced P -wave velocities and lower rock densities, are distinguished in the section 67 km deep (crust/mantle boundary zone and upper lithospheric mantle). Dilatation became the main reason behind the intensive uplift of these mountain systems and, partially, Tibet. The sections with depths of 158 and 293 km revealed heterogeneous structures of the upper mantle of Central Asia. In its eastern part, P -wave velocities were significantly reduced by the influence of Tibetan and Khangai intramantle plumes. Here, lateral extension exceeded lateral shortening, and the lithosphere could not transfer the pressure of the Indian Platform to the northern tectonic zones. Dilatation of the upper mantle caused the uplift of Tibet and the Khangai Plateau. Plume-related currents in upper mantle caused left-lateral strike-slips along latitudinal faults. In the south and west of Central Asia, P -wave velocities and the density of the upper mantle increase. In the south, the lithosphere of the Indian Platform thickens and underthrusts the Himalayas and Southern Tibet. Active thrusts, right-lateral strike-slips, and oblique-slip thrusts in the western and northwestern parts of Central Asia express horizontal compression of lithospheric blocks. The heterogeneous density of the lithosphere resulted in rotation of the compressed blocks, so that shear decreased and even faded along the faults.