华北克拉通中西部地壳S波速度结构及其地质意义  

Crustal S-wave velocity structure in the western and central North China Craton and its geological significance

作　　者：侯爵 潘佳铁[1] 李永华[1] 武振波 俞贵平 徐涛[2,6] HOU Jue;PAN JiaTie;LI YongHua;WU ZhenBo;YU GuiPing;XU Tao(Institute of Geophysics,China Earthquake Administration,Beijing 100081,China;State Key Laboratory of Lithospheric Evolution,Institute of Geology and Geophysics,Chinese Academy of Sciences,Beijing 100029,China;University of Chinese Academy of Sciences,Beijing 100049,China;College of Geophysics,Chengdu University of Technology,Chengdu 610059,China;College of Earth Sciences,Guilin University of Technology,Guilin 541004,China;Innovation Academy for Earth Science,CAS,Beijing 100029,China)

机构地区：[1]中国地震局地球物理研究所,北京100081 [2]中国科学院地质与地球物理研究所,岩石圈演化国家重点实验室,北京100029 [3]中国科学院大学,北京100049 [4]成都理工大学地球物理学院,成都610059 [5]桂林理工大学地球科学学院,桂林541004 [6]中国科学院地球科学研究院,北京100029

出　　处：《地球物理学报》2023年第5期1960-1975,共16页Chinese Journal of Geophysics

基　　金：国家自然科学基金(U1839210,91755215,42174077,41874065);王宽城教育基金(GJTD-2019-04)联合资助。

摘　　要：华北克拉通是世界上最古老的克拉通之一.我们利用布设于华北中部的ChinArray计划461个宽频带地震台阵的连续波形资料,基于背景噪声成像技术,获得了克拉通中西部5~45 s的Rayleigh波群速度频散曲线,并利用线性反演方法获得了研究区地壳上地幔顶部的S波速度结构.密集流动地震台阵使我们能够揭示研究区精细的地壳上地幔顶部速度变化,以深入探讨华北克拉通中西部深部结构及其对岩浆和地震的控制作用.8 km深度的S波速度切片显示低速与高速异常分别与地表的盆地和山脉对应良好.不同经度和纬度方向的S波速度剖面均表明,西部克拉通地壳大致可以分为上、中、下地壳三层.克拉通西部鄂尔多斯块体的下地壳S波速度介于3.7~3.8 km·s^(-1),暗示其下地壳以长英质岩石为主.大同火山区下方的S波低速异常从中地壳延伸至上地幔顶部,推测源自软流圈的地幔热流提供了近垂直的主干上涌通道,并控制了该区新生代岩浆活动.强震集中分布在上地壳高速体内部或高低速相间区,其下地壳乃至上地幔顶部都呈现明显的低速异常,推测源自上地幔/下地壳的深部热流沿地壳尺度的陡深断裂上侵,诱发上覆高应力刚性块体发生蠕动破裂与应力释放,进而诱发大震.The North China Craton(NCC)is one of the oldest cratons in the world.In order to study the deep structure in the central and western parts of the NCC and its control on magma and earthquakes,we derive a new high-resolution 3-D shear wave velocity model of the central and western NCC crust and uppermost mantle using ambient noise tomography.The cross-correlation of vertical-component continuous noise recordings from 461 temporary seismic stations belonging to the ChinArray project provides Rayleigh wave group velocity dispersions in the period range 5~45 s.These dispersion data at each model grid are inverted to obtain 1D shear-wave velocity models,and then construct a pseudo-3-D model of crustal and uppermost mantle.The dense path coverage allows us to examine lateral variations of shear wave velocity structure in unprecedented detail,shedding new light on the deep structure and its impacts on magma activities and earthquakes.Our velocity model at depth of 8 km show that surface basins and mountains are characterized with low-velocity and high-velocity anomalies,respectively.The S-wave velocity profiles in different longitude and latitude directions show that the crust of the western craton can be roughly divided into upper,middle and lower crust.The S-wave velocity in the lower crust of the Ordos block ranges between 3.7 and 3.8 km·s^(-1),suggesting that the lower crust is dominated by felsic rocks.The low S wave velocity anomaly below the Datong volcanic area extends from the middle crust to the uppermost mantle,implying that the upwelling mantle provides a near-vertical channel and controls the formation and development of Cenozoic magmatism in this area.The strong earthquakes are concentrated in the interior of the high-velocity bodies,or alternating regions of high and low velocities in the upper crust,and the middle-to-lower crust is characterized with low velocity,implying that creep rupture and stress release of stressed rigid blocks associated with the deep heat flow of the uppermost mantle/lower crust

关 键 词：华北克拉通 地壳结构 中部造山带 背景噪声 孕震背景 

分 类 号：P315[天文地球—地震学]