青藏高原东北缘岩石圈厚度与上地幔各向异性

利用青海地震台网和甘肃地震台网2007-2009年记录的远震波形资料,提取S波接收函数和SKS分裂参数,得到了青藏高原东北缘的三维岩石圈厚度分布和上地幔各向异性特征.S波接收函数结果表明:昆仑-阿尼玛卿缝合带以南的松潘-甘孜地块东北缘和西秦岭造山带下方岩石圈较薄,厚度为125~135 km;昆仑-阿尼玛卿缝合带以北具有较厚的岩石圈,在昆仑和祁连地块下方岩石圈厚达145~175 km,并向柴达木盆地(175~190 km)和克拉通(鄂尔多斯南部约为170 km、阿拉善南缘约为200 km)下方增厚.上地幔各向异性结果显示:东北缘地区的SKS快波偏振方向为NW-SE向,与前人得到的昆仑断裂带南侧的快波方向存在较大差异,南侧自高原内部呈顺时针旋转,表明昆仑断裂带可能为上地幔变形的转换带.SKS快、慢波延迟时间为0.8~1.9 s,且在昆仑-阿尼玛卿缝合带以北,延迟时间与岩石圈厚度呈正相关关系,推断该区各向异性主要来源于地幔盖层的初期伸展变形.

Lithospheric thickness and upper mantle anisotropy beneath the northeastern Tibetan Plateau

We present S receiver functions and SKS splitting measurements from the China Seismograph Network located in the Qinghai and Gansu provinces. Teleseismic data are used to interpret the structure of the Lithosphere-Asthenosphere Boundary (LAB) and the upper mantle deformation beneath the northeastern Tibetan Plateau (NETP) in regions north of the east Kunlun fault. Based on our observations, the depth of the LAB is 125~135 km beneath the northeastern Songpan-Ganzi block and the west Qinling orogen, 145~175 km beneath the Kunlun and Qilian block, and deepens to the Qaidam basin (175~190 km), Ordos craton (170 km), and Alashan platform (200 km). The NETP has a nearly uniform fast wave direction of NW-SE. These observations are different from those to the south of the Kunlun fault which are rotating clockwise from the inner plateau. The difference between fast directions across the Kunlun fault implies a sudden variation of the upper mantle deformation occurred there. Shear wave splitting delay times vary from 0.8 to 1.9 s. And data from beneath regions north of the Kunlun-Ayimaqin suture showed that delay time was positively correlated with lithospheric thickness. This indicates that the anisotropy may develop in the uppermost mantle, such as the lithosphere, beneath the NETP.