华北中西部和青藏高原东北缘上地幔各向异性变形特征  

Upper mantle anisotropy and implications beneath the central and western North China and the NE margin of Tibetan Plateau

作　　者：常利军[1] 丁志峰[1] 王椿镛[1] CHANG LiJun;DING ZhiFeng;WANG ChunYong(Institute of Geophysics,China Earthquake Administration,Beijing 100081,China)

机构地区：[1]中国地震局地球物理研究所,北京100081

出　　处：《地球物理学报》2021年第1期114-130,共17页Chinese Journal of Geophysics

基　　金：国家重点研发计划(2017FYC1500200);国家自然科学基金(41774061,42074053,U1839209,41474088)资助.

摘　　要：基于华北中西部和青藏高原东北缘3个流动台阵共480个台站新得到的远震XKS(SKS、SKKS和PKS)波分裂结果,并结合研究区已得到的987个台站的分裂结果,获得了高分辨率的上地幔各向异性图像.分析表明,鄂尔多斯块体的时间延迟较小,反映了其稳定性和弱的各向异性变形特征,可能保留了古老克拉通根的“化石”各向异性,但其靠近边缘的局部区域表现出与相邻边缘相一致的各向异性特征,反映了其局部区域受到了与其相邻边缘的构造活动影响.青藏高原东北缘、阿拉善块体和鄂尔多斯块体西缘快波方向主要为NW-SE方向,鄂尔多斯块体北缘主要为NNW-SSE方向,反映了青藏高原沿NE方向推挤过程中岩石圈沿NW-SE方向和NNW-SSE方向发生了伸展变形;位于四川盆地和鄂尔多斯块体两个刚性块体间的秦岭造山带的快波方向为近E-W方向或NWW-SEE方向,时间延迟较大,推测岩石圈东向挤出和软流圈东流共同促进了观测的各向异性;在鄂尔多斯块体南部边缘,快波方向自西向东逆时针沿西南缘六盘山的NW-SE方向转到南缘渭河地堑的近E-W方向再到东南缘太行山的NEE-SWW方向,推断该区域可能存在一个绕刚性块体的逆时针软流圈绕流,与上覆岩石圈左旋简单剪切变形产生了观测的各向异性,并一起驱动了鄂尔多斯块体的逆时针旋转.作为华北克拉通东西部的过渡带,华北中部的各向异性相对复杂,其东部快波方向为近E-W方向或NWW-SEE方向,时间延迟较大,其各向异性主要反映了太平洋板块西向俯冲作用引起的地幔流;其西北部吕梁山的各向异性主要由岩石圈沿NNW-SSE到NW-SE的拉张变形导致,而西南部太行山的各向异性还反映了软流圈绕流作用.鄂尔多斯块体东北缘大同火山区存在一个快波方向顺时针快速旋转且时间延迟较小的区域,可能与火山群下地幔岩浆上涌形成的局部地幔对流相关.紧邻华北北部�The central and western North China and the NE margin of the Tibetan Plateau connects east China and west China,which are dominated by horizontal extension and compression,respectively.This study area consists of a variety of tectonic units,including the Songpan-Garzêblock and Qilian orogenic belt,which are terranes of the northeastern Tibetan Plateau;the Alxa block,the Ordos block and its surrounding grabens and orogenic belts-the central and western North China;and the mid-south Central Asian Orogenic Belt(CAOB).To the west of the study area,the ongoing convergence between India and Eurasia plate caused the uplift,crustal thickening and lateral escape of the Tibetan Plateau.To the east,the westward subduction of the Pacific plate to the Eurasian plate strongly affected the tectonic movement of the plate margin and interior.Here seismic activity is strong and tectonic structure is complex.Thus,the study area provides a unique nature laboratory for understanding continental interiors and lithosphere's deformation.Due to the intrinsic linking between anisotropy,finite strain and tectonic process,seismic anisotropy studies have been used widely to constrain on deformation pattern of the crust and lithosphere mantle during an orogenic process.In this study,Based on the polarization analysis of teleseismic XKS(SKS,SKKS and PKS)waveforms recorded at 480 stations from 3 temporary seismic array deployed in the central and western North China and the northeastern Tibetan Plateau,the fast-wave directions and delay times were measured by using the grid searching method of minimum tangential energy and stacking analysis,and we used the 480 new shear wave splitting observations from dense temporary seismic array and 987 published results to map out variations in the deformation of the study area.The comparative analysis of anisotropy with surface deformation,geological structure and lithospheric structure shows that,on the whole,the value of delay time in the Ordos block is less than that in its margins and other tectonic u

关 键 词：地震台阵 横波分裂 岩石圈变形 软流圈地幔流 

分 类 号：P315[天文地球—地震学]