Constraining the crustal structure under the central and western Tian Shan based on teleseismic receiver functions and gravity anomalies

Abstract

The Tian Shan is a vast range that spans several countries in Asia. Understanding its evolutionary history may provide valuable insights into intracontinental orogenic dynamics. In this study, we explored the crustal characteristics of the Tian Shan and their relationships to the tectonic evolution of the region. A new H-stacking method that combines the P receiver function and gravity anomalies was used to estimate the thickness and ratio of P- to S-wave velocities (vP/vS) for 91 broadband seismic stations in the central and western Tian Shan. Our results revealed significant lateral variations in crustal thickness and vP/vS. A ∼45-km-thick crust and an intermediate-high vP/vS (∼1.74–1.84) were found in the Kazakh Shield and Tarim Basin, which we interpreted to indicate a mafic crystalline basement and lower crust. The central Tian Shan varied greatly in crustal thickness (40–64 km) and vP/vS ratio (1.65–2.00), which may be due to crustal shortening, mafic underplating, and crustal melting. In contrast, we observed a relatively thin crust (42–50 km) with an intermediate vP/vS ratio (∼1.78) in the western Tian Shan. The differences in the crustal structures between the western and central Tian Shan imply that the Talas-Fergana Fault may be trans-lithospheric.