Crustal and uppermost mantle structure of the northeastern Qinghai-Xizang Plateau from joint inversion of surface wave dispersions and receiver functions with P velocity constraints
Pei Zhang , Xiaodong Song , Jiangtao Li , Xingchen Wang , Xuezhen Zhang
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引用次数: 0
Abstract
Lithospheric structure beneath the northeastern Qinghai-Xizang Plateau is of vital significance for studying the geodynamic processes of crustal thickening and expansion of the Qinghai-Xizang Plateau. We conducted a joint inversion of receiver functions and surface wave dispersions with P-wave velocity constraints using data from the ChinArray II temporary stations deployed across the Qinghai-Xizang Plateau. Prior to joint inversion, we applied the H-κ-c method (Li JT et al., 2019) to the receiver function data in order to correct for the back-azimuthal variations in the arrival times of Ps phases and crustal multiples caused by crustal anisotropy and dipping interfaces. High-resolution images of vS, crustal thickness, and vP/vS structures in the Qinghai-Xizang Plateau were simultaneously derived from the joint inversion. The seismic images reveal that crustal thickness decreases outward from the Qinghai-Xizang Plateau. The stable interiors of the Ordos and Alxa blocks exhibited higher velocities and lower crustal vP/vS ratios. While, lower velocities and higher vP/vS ratios were observed beneath the Qilian Orogen and Songpan-Ganzi terrane (SPGZ), which are geologically active and mechanically weak, especially in the mid-lower crust. Delamination or thermal erosion of the lithosphere triggered by hot asthenospheric flow contributes to the observed uppermost mantle low-velocity zones (LVZs) in the SPGZ. The crustal thickness, vS, and vP/vS ratios suggest that whole lithospheric shortening is a plausible mechanism for crustal thickening in the Qinghai-Xizang Plateau, supporting the idea of coupled lithospheric-scale deformation in this region.
青藏高原东北部地下岩石圈结构对研究青藏高原地壳增厚和扩张的地球动力学过程具有重要意义。我们利用布设在青藏高原的 ChinArray II 临时站的数据,对接收函数和面波频散与 P 波速度约束进行了联合反演。在联合反演之前,我们对接收函数数据采用了H-κ-c方法(Li JT等,2019),以校正地壳各向异性和倾斜界面引起的Ps相和地壳多相到达时间的后方位角变化。联合反演同时得出了青藏高原的高分辨率vS、地壳厚度和vP/vS结构图像。地震图像显示,地壳厚度从青藏高原向外递减。鄂尔多斯块体和阿拉善块体的稳定内部表现出较高的速度和较低的地壳 vP/vS 比值。而在祁连造山带和松潘-甘孜地块(SPGZ)下,速度较低,vP/vS比值较高,这两个地块地质活跃,机械强度较弱,尤其是在中下地壳。热星体流引发的岩石圈脱层或热侵蚀是在松潘-甘孜地块观测到的最上层地幔低速带的成因。地壳厚度、vS和vP/vS比值表明,整个岩石圈缩短是青藏高原地壳增厚的一个合理机制,支持了该地区岩石圈尺度耦合变形的观点。
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