华南块体西南缘地壳结构特征及其地质意义  

Characteristics of crustal structure and its geological significance of the southwestern margin in South China

作　　者：李鹏宇 张智[1,2] 张晓青 刘锋 徐涛[3,4] 俞贵平[1,2] 王敏玲[1,2] 侯爵 李奇 LI Pengyu;ZHANG Zhi;ZHANG Xiaoqing;LIU Feng;XU Tao;YU Guiping;WANG Minling;HOU Jue;LI Qi(College of Earth Sciences,Guilin University of Technology,Guilin 541006,China;Collaborative Innovation Center for Exploration of Nonferrous Metal Deposits and Efficient Utilization of Resources in Guangxi,Guilin University of Technology,Guilin 541006,China;Institute of Geology and Geophysics,Chinese Academy of Sciences,Beijing 100029,China;State Key Laboratory of Lithospheric Evolution,Chinese Academy of Sciences,Beijing 100029,China;Institute of Geophysics,China Seismological Bureau,Beijing 100081,China)

机构地区：[1]桂林理工大学地球科学学院,广西桂林541006 [2]桂林理工大学有色金属矿产勘查与资源高效利用省部共建协同创新中心,广西桂林541006 [3]中国科学院地质与地球物理研究所,北京100029 [4]中国科学院岩石圈演化国家重点实验室,北京100029 [5]中国地震局地球物理研究所,北京100081

出　　处：《桂林理工大学学报》2023年第4期570-580,共11页Journal of Guilin University of Technology

基　　金：国家自然科学基金项目(41974048;42374059;42104042);广西自然科学基金项目(2023GXNSFDA026055)。

摘　　要：新元古代早期以来,扬子和华夏块体开始碰撞拼合并形成了华南块体,之后又经历了多期复杂的构造-岩浆活动。华南块体地壳厚度和分层结构的研究,有助于进一步认识华南块体碰撞活动历史,对与之相关的中生代大规模成岩成矿作用有启发意义。本文基于华南西南缘162个宽频带固定台站记录的16个月垂直分量连续波形数据,利用背景噪声互相关技术提取经验格林函数,并开展了面波层析成像研究,获得了3~45 s的Rayleigh波相速度分布图和50 km以浅的地壳和上地幔顶部S波速度结构。不同深度的S波速度切片显示,扬子块体的地壳厚度整体大于华夏块体的地壳厚度,两者在20 km以深的中下地壳和上地幔顶部存在明显的速度差异,高、低速异常的分界大致位于郴州-临武断裂以西。跨郴州-临武断裂的3条S波速度剖面则进一步显示,以郴州-临武断裂为代表的上地壳逆冲断层和中下地壳北西西倾向的断裂均汇聚于中地壳低速的脆韧性过渡带,推测这些构造可能是扬子和华夏块体碰撞后形成的逆冲推覆构造,并在燕山期伸展背景下进一步活化为地壳或超壳尺度的拆离断层。结合已有地质、地球物理资料,推测郴州-临武断裂为扬子和华夏块体在华南西南缘的构造边界,且扬子和华夏块体碰撞拼贴时,后者的上、下地壳可能发生了解耦。The Yangtze and Cathaysian blocks began to collide and form the South China block in the Neoprot-erozoic Era.The South China block underwent multiple complex tectonic magmatic activities.The study of crust thickness and stratification structure of South China block is helpful to further understand the history of the colli-sion of South China plate.It is instructive to the related large-scale diagenesis and mineralization in Mesozoic.This paper is based on 16 months continuous waveform data of vertical component recorded by 162 broadband fixed stations on the southwest edge of the South China,and empirical Green functions are extracted by ambient noise cross-correlation technology.Surface wave tomography is carried out.Rayleigh wave phase velocity maps of 3-45 s and S-wave velocity(VS)structures of crust and uppermost mantle above 50 km are obtained.VS slices at different depths show that the crustal thickness of the Yangtze block is generally greater than that of the Cathay-sian block.There is a significant velocity difference between the middle-lower crust and the uppermost mantle at a depth of more than 20 km.The boundary between high and low velocity anomalies is roughly located to the west of the Chenzhou-Linwu fault(CLF).The three VS profiles across the CLF further show that the upper crus-tal thrust faults represented by the CLF and the NWW trending faults of the middle-lower crust all converge in the brittle-ductile transition zone with low velocity of the middle crust.It is speculated that these structures may be the thrust structures formed by the collision of the Yangtze and Cathaysian blocks.Under the Yanshanian ex-tensional setting,they were further reactivated into crustal or supracrustal scale detachment faults.Geological and geophysical data indicate that the CLF is the tectonic boundary of the Yangtze and Cathaysian blocks in southwestern margin of South China,and the upper and lower crust of the latter might have been decoupled dur-ing the collision period between the Yangtze and Cathaysian block

关 键 词：华南块体 扬子-华夏块体 背景噪声层析成像 地壳结构 郴州-临武断裂 

分 类 号：P313.2[天文地球—固体地球物理学] P315.31[天文地球—地球物理学]