秦岭造山带及邻区上地壳精细速度结构研究  

Detailed upper crustal velocity structure beneath the Qinling Orogen and adjacent region

作　　者：李文辉[1] 王海燕[1] 高锐[1,2] 卢占武 李洪强[3] 侯贺晟[3] 熊小松[3] 叶卓[3] LI Wenhui;WANG Haiyan;GAO Rui;LU Zhanwu;LI Hongqiang;HOU Hesheng;XIONG Xiaosong;YE Zhuo(Institute of Geology,Chinese Academy of Geological Sciences/Key Laboratory of Deep Earth Dynamics of Ministry of Natural Resources,Beijing 100037,China;School of Earth Sciences and Engineering,Sun Yat-sen University,Guangzhou 510275,China;China Deep Exploration Center,Chinese Academy of Geological Sciences,Beijing 100037,China)

机构地区：[1]中国地质科学院地质研究所/自然资源部深地动力学重点实验室,北京100037 [2]中山大学地球科学与工程学院,广东广州510275 [3]中国地质科学院地球深部探测中心,北京100037

出　　处：《地学前缘》2022年第2期198-209,共12页Earth Science Frontiers

基　　金：国家自然科学基金项目(41404072,42174124,41574094);中国地质调查局地质调查项目(DD20190016);国家科技专项“深部探测技术实验与集成(SinoProbe-02)”。

摘　　要：秦岭造山带是华北板块和扬子板块南北两个大陆边缘长期演化的产物,各部分性质和时代不同,是一个复杂的构造混杂体。由于其所处位置的重要性,演化时间上的长期性、多旋回性,空间上的多样性、变异性,一直是地质和地球物理学研究的热点。为了沟通该区复杂的浅表地质现象与深部结构成像,获取更精细的上地壳结构成为厘定秦岭造山带不同块体之间接触关系,揭示其地球动力学演化过程的关键。本文对一条长450 km、南北向跨越鄂尔多斯地块南缘、渭河地堑、秦岭造山带、大巴山逆冲推覆带和四川盆地北缘的宽角反射与折射地震剖面采集的15个大炮数据进行了层析成像研究。本研究对690个初至走时拾取数据使用有限差分算法,采用变网格尺度及平滑参数的迭代策略,经20次迭代反演,走时均方根误差降至0.105 s,收敛良好。成像结果精细刻画了渭河地堑的低速沉积特征,系一个南深北浅的断陷盆地,最深处可达7 km,其发育主要受秦岭北缘断裂、乾县—富平断裂及渭河断裂控制。秦岭北缘断裂与安康—竹山断裂之间的秦岭造山带上地壳呈高速特征,横向变化剧烈,仅残余若干较浅的山间盆地。与南部四川盆地稳定沉积相比,大巴山逆冲推覆带下方沉积层速度结构不统一,反映了逆冲推覆作用的改造,但整体仍保留了3~6 km的沉积厚度。本文分析认为剖面中部的秦岭地区是古生代—早中生代南北板块汇聚的核心地带,之后造山带两翼的南、北陆缘分别于燕山期和新生代转入逆冲推覆和伸展两种迥异的构造环境,而现今研究区的上地壳构造格局是三次事件叠加的结果。The geologic framework of the Qinling Orogen and adjacent region is developed as a result of the convergence of the North China Craton and Yangtze Craton during a long and complex evolutionary history. Detailed upper crustal structure connecting the superposed surface geological phenomena with geophysical images is a key for understanding the geodynamics of the convergence process. The Qinling wide angle reflection and refraction seismic profile extends from the Ordos basin, across the Weihe graben, Qinling orogeny, Dabashan thrusting nappe, to the Sichuan basin. The seismic waves from 15 explosions were recorded on 281 DFZ recorders, of which 690 arrivals of refracted waves from sediments and basement(Pg) were typically picked, and finite-difference tomography algorithm was used to obtain the upper crustal velocity structure. After 20 iteration, the RMSD for the resulting arrival time was 0.105 s, with good convergence. The final P-wave velocity model contains the following features of tectonic significance:(1) The Weihe graben is a typical down-faulted basin with the deepest sediments, as deep as 7 m, in the south, and its formation is controlled by the Qinling northern border fault, Weihe fault and Qianxian-Fuping fault.(2) The upper crustal structure of the Qinling orogen varies significantly with generally high velocity.(3) Sediments of 3-6 km thick beneath the Dabashan Mountain are preserved, but the velocity structure is not uniform, which reflects the thrusting induced reformation.

关 键 词：宽角反射与折射 秦岭造山带 渭河地堑 大巴山 地震层析成像 

分 类 号：P315.23[天文地球—地震学]