Research progress on seismic structures of crust and mantle beneath Tien Shan and their geodynamic implications

The mechanisms causing the uplifting of the Tien Shan, one of the largest and most active intracontinental orogenic belts on Earth, have been vigorously debated for decades. Seismic investigation is a fundamental tool used for deep structural exploration and is key to understanding continental geodynamics. As such, in this study, we reviewed the recent research progress on the crustal and upper-mantle structures of the Tien Shan and the remaining controversies. The results showed that the Tien Shan and adjacent basins exhibit contrasting structural and physical properties from the crust down to the upper mantle in various aspects, such as crustal thickness, Moho morphology, mantle transition-zone thickness, seismic velocity, and seismic attenuation. The mountainous areas have complex crustal seismic anisotropy patterns, whereas orogen-parallel anisotropic fabrics dominate at upper mantle depths. Low-velocity anomalies pervasively exist in the mid-lower crust and uppermost mantle of Tien Shan. Taken together, these observations provide evidence of the important roles played by intracontinental subduction and mantle upwelling in Cenozoic orogenesis of the Tien Shan. However, further development of our understanding of the geodynamics in Tien Shan has been hindered by the low imaging resolution of seismic anisotropy, lithosphere-asthenosphere boundary, and mantle transition zone in eastern Tien Shan. And some important geophysical parameters and their implications are still far from being well-understood. Future deployment of dense temporary seismic arrays in the eastern Tien Shan and joint inversion of multiple and complementary geophysical data will considerably increase the resolution of seismic models and ultimately enhance our knowledge of geodynamic evolution in compressional intracontinental orogens.