Seismic tomography of Tianshan-Junggar region  and its lithospheric structure

Based on 24 904 P-wave arrival time data from 1132 events recorded at 140 stations in two seismic profiles across Tianshan mountain and in Xinjiang regional seismic network, tomographic images of P-wave velocity are achieved beneath Tianshan-Junggar region by travel time inversion. Result of checkboard tests indicates that the reliability of velocity perturbation recovering is relatively high for the region beneath the two profiles themselves, along Tianshan and eastern Junggar. The inversion result of P-wave velocity perturbations clearly tells the boundary between the high velocity zone in Tianshan terrane and low velocity zone in the basins on both sides of Tianshan. Moreover, the result also reveals the low velocity beneath inner-Tianshan basin and in the upper mantle. On the tomographic image we can see distinguished difference between eastern and western Tianshan. In the crust beneath western Tianshan a typical structure of knocking together from both northern and southern part towards central can be found, while beneath eastern Tianshan the structure shows strong coupling between Tianshan mountain and Junggar basin. Nevertheless at the depth in top mantle both areas display a low velocity zone named as Central Tianshan LVZ, behaving as medium upgoing flow in the west and as block subducting in the east. At the depth of upper mantle in Altai area there is a large size high velocity zone, which may be attributed to the intruding of intermediate-basaltic magma.The magmatic differentiation in shallow crust may form hybrid deposits.