Crustal thickness (H) and Vp/Vs ratio (κ) images beneath the central Tien Shan revealed by the H-κ-c method

As an active intracontinental orogenic belt within the far field influence of the India-Eurasia collision, the Tien Shan is a natural laboratory to study the mechanisms of the large-scale mountain building. In this study, we image crustal seismic structures beneath the central Tien Shan using the H - κ - c method with the harmonic corrections on Ps and its crustal multiples ( PpPs , PpSs + PsPs ) in P -wave receiver functions (RFs). The RFs are calculated from three-component seismograms recorded by 43 broadband stations located in central Tien Shan and surrounding areas. The robust and high-resolution images of the crustal thickness ( H ) and average Vp / Vs ratio ( κ ) are finally obtained. From our observations, the crustal thickness beneath the central Tien Shan is larger (50– 65 km) than those beneath the Kazakh Shield (~45 km) and Tarim Basin (~42 km). The κ image denotes a general distribution of κ which is higher than 1.73 in most parts of the central Tien Shan, as well as the margins of the Kazakh Shield and Tarim Basin, while lower than 1.73 only in some sporadic areas of this orogenic belt. Our seismic results suggest the complex intracontinental collision with the inhomogeneous crustal thickening in the mountain building. Moreover, the κ image implies the partial melting within the crust beneath the central Tien Shan. Combining with previous seismic studies, we infer that the magmatic intrusion of the hot upwelling mantle materials induces the partial melts within the crust, and also contributes to the rejuvenation of the Tien Shan orogenic belt. • Crustal structures beneath the central Tien Shan are effectively constrained with the H-κ - c method. • The nonuniformly thickened crust suggests that there is a complex intracontinental collision in the mountain building. • The generally high κ (> 1.73) imply the partial melting associated with the magmatic intrusion of hot upwelling mantle.