The Lithosphere Structure And Basin-Range Coupling In The Boundary Area Of Tianshan Mountains And Tarim Basin

The Tianshan Mountains was reactivated during the Cenozoic and the tectonics was still active today. The Tianshan uplifting goes with the adjacent Tarim subsiding, both of them are a natural laboratory for the intracontinental orogenesis belt. In this paper, we deploy a linear seismic array of223-component broadband digital stations across the boundary area to study the lithospheric structure, analyze the teleseismic body waveform data by receiver functions, discuss the coupling means and geodynamics mechanism and draw some new conclusions.The receiver function profile reveals the lateral and vertical inhomogeneity in the crust and upper mantle of the boundary area. The upper crust is covered with significant thickness of surface sediments, while the moderate crust is an obvious low velocity layer, and the lower crust&upper mantle also exist relatively low-velocity area, the whole moho slants westward slightly. The overage thickness of the crust is42～50km, Korla area is the thinnest which is only42km, the others is about50km. The Poisson’s rations are much higher than the normal crust range in this area, the value range is0.28-0.33except the Kuqa region, the higher Poisson’s ration is caused by the lower crust partial melting and the uprush mantle materials along fracture. The seismicity is mainly based on moderate small and shallow earthquake and two advertaged seismogenic layers are developed in this area. There is much difference between the western and eastern parts which also reflects the different of the subduction zones of Tarim basin into the Tianshan Mountains. These differences are caused by the Pamirs’s N compressional stress and the Tarim’s clockwise rotation.Studies on the Basin-Range coupling relationships show that there is much different in depth between eastern and western parts of the subduction zones which is caused by the stress field and the activity of the faults. In the east, the coupling relationship is relatively single, the upper crust display flexure deformation and superimposing by layers during the thrusting from the mountain to the basin, while the lower crust is subduction from basin to mountain. In the west, the faults develop very much and compress the stratum; the detachment surface of the thrusting nappe expands continuously as the result of activities of faults. The underthust angle and depth in western of the lower crust subduction are probable stronger than the eastern. At last, under the action of NS regional tectonic stress field, this region develops a tectonic pattern of two uplift-and-depressions. The crustal low velocity layer is the detachment surface of upper-lower crust, it is also the important decoupling interface of the crust which affects the coupling relationship of the crust in different depth, and the fault plane and the detachment surface are the decoupling interface of the stratum.