Low-velocity anomaly in the lithosphere of eastern Central Tianshan imaged with seismic waveform fitting

As one of the most important active intracontinental orogenic belts in the world, the Tianshan has experienced the closure of the Paleo-Asian Ocean, rejuvenation, and intracontinental orogeny caused by the far-field effect of the India-Eurasia collision. Here, based on the delayed seismic waveforms recorded by the China National Seismic Network (CNSN) from local and teleseismic earthquakes, we find an obvious low-velocity anomaly (LVA) of 6% at depths of 35–110 km, which is just beneath the eastern Central Tianshan, near the highest peak of Yilianhabierga Mountain. We constrain the lateral distribution of the LVA with arrival delays of teleseismic P waves, and the vertical distribution and velocity contrast of the LVA with waveform fitting of local seismic P waves. Combined with previous results, the LVA could be related to the rejuvenation of the Tianshan caused by the India-Eurasia plate collision. After the bidirectional subduction of the Tarim lithosphere and Junggar lithosphere into the Tianshan upper mantle, the hot upwelling asthenosphere filled the space in which the delaminated lithosphere was previously occupied. Then, the hot upwelling asthenosphere heated the lithosphere and resulted in the partial melting of the accretionary wedge, which is normally believed to have high water content. Our results can provide important insight into the lithospheric deformation processes and tectonic evolution in the Tianshan.