Small-scale upper mantle convection and orogeny of Tianshan Mountains in China

Abstract

In this study, from the travel time data recorded in the Tianshan passive seismic array experiment, we present the P-wave velocity structure of the upper mantle down to 660 km along the Kuqa-Kuitun profile in terms of seismic tomography technique. Based on the P-wave velocity model, we derive the corresponding 2D upper mantle density model. The 2D small-scale convection of the upper mantle underneath the Tianshan Mountains in China driven by the density anomalies is simulated using the hybrid finite element method combining with the marker-in-cell technique. The main features of the upper mantle convection and the reciprocation between the convection and mountain building are investigated. The results manifest that (1) in the upper mantle underneath the Junggar basin and North Tianshan exists a counterclockwise convection, which scale is ~ 500 km; (2) underneath the Tarim basin and South Tianshan exists a clockwise northward convection, which is relatively weak; (3) the convective velocity at the top of the upper mantle underneath the Tianshan Mountains in China should not be less than 20 mm/a, while considering the dependent of convective velocity on the viscosity; (4) the northward extrusion of the Tarim block plays a key role in the Cenozoic Tianshan mountain building and the present-day tectonic deformation of the Tianshan range is related closely to the upper mantle convection; and (5) the northward subduction of the Tarim block does not influence obviously the upper mantle convection.Tianshan orogeny, mantle convection, orogeny, finite element method, marker-in-cell method

Crustal attenuation structure of the Tianshan tectonic belt and its spatiotemporal variations

“…Using dense array data, several studies have inverted the fine S-and P-wave velocity structures in the crust and upper mantle across the TTB and revealed significant deformation in the S-N direction, rock bodies with marked low S-wave velocity, and an arrangement of bodies with alternating high and low velocities in the crust beneath the TTB (Shao et al, 1996;Guo et al, 2006;Li et al, 2007;Xiong et al, 2011). Furthermore, the lithosphere under the TTB is relatively thin, which may be related to processes, such as continental collision-suture and delamination, along with the upliftment of the orogenic belt and subsidence of Moho (Schubert et al, 2001;Kumar et al, 2005;Liu, and Guo et al, 2007).…”