华南陆块西南缘上地幔顶部三维密度结构及其地质意义  

Three-dimensional density structure and geological significance of uppermost mantle beneath the southwestern South China Block

作　　者：杨富强[1,2] 张思文 廖海志 梁青 莫亚军[2] 李叶飞[2] 陈超 YANG FuQiang;ZHANG SiWen;LIAO HaiZhi;LIANG Qing;MO YaJun;LI YeFei;CHEN Chao(School of Geophysics and Geomatics,China University of Geosciences(Wuhan),Wuhan 430074,China;Geophysical Survey Institute of Guangxi Zhuang Autonomous Region,Liuzhou Guangxi 545005,China;Hubei Subsurface Multi-scale Imaging Key Laboratory,China University of Geosciences(Wuhan),Wuhan 430074,China)

机构地区：[1]中国地质大学(武汉)地球物理与空间信息学院,武汉430074 [2]广西壮族自治区地球物理勘察院,广西柳州545005 [3]中国地质大学(武汉)地球内部多尺度成像湖北省重点实验室,武汉430074

出　　处：《地球物理学报》2024年第10期3766-3780,共15页Chinese Journal of Geophysics

基　　金：广西地矿局部门前期项目(桂地矿综研[2023]9号、桂地矿综研[2022]16号)资助。

摘　　要：华南陆块自新远古代拼合以来,经历了多期构造-岩浆活动,岩石圈及其深部结构较为复杂,前人对西南缘扬子与华夏地块缝合带位置的厘定仍有不同认识.研究该区域上地幔顶部密度结构,有助于进一步认识扬子—华夏地块拼合对岩石圈的改造,对确定扬子—华夏地块在广西地区的边界位置有重要意义.基于卫星布格重力异常,利用地震波速度-密度转换关系构建的上地幔密度参考模型作为约束,反演剩余的岩石圈和上地幔重力异常,获得了岩石圈至300 km深度的上地幔顶部三维密度结构.密度结构揭示了华南陆块西南部的岩石圈—软流圈界面起伏和上地幔物质密度的不均匀分布.分析结果表明广西中部存在高密度岩石圈物质下沉,南部低密度的软流圈物质上涌,取代已拆沉的岩石圈根并向上侵入地壳,是地表出露花岗岩的来源.结合区内基底特征和碎屑锆石陆缘来源,推断沿广西富川—武宣—隆安—凭祥一线为扬子—华夏地块在华南陆块西南缘(广西段)缝合位置.The South China Block has experienced various stages of tectonic-magmatic activity since the Neoproterozoic collision. The lithosphere and deep structure appear to be relatively complex. The location of the suture zone at the southwestern margin between the Yangtze and Cathaysia blocks remains controversial. The density structure of the uppermost mantle can improve our understanding of the lithosphere transformation after the collision of the Yangtze and Cathaysia blocks. Furthermore, it is crucial to locate the suture zone in Guangxi area. We conduct an inversion of the residual gravity anomalies of the lithosphere and uppermost mantle derived from the satellite Bouguer gravity anomaly. The upper mantle density reference model that serves as a constraint for inversion is created by employing the seismic wave velocity-density conversion relationship. We obtain a three-dimensional density structure of the uppermost mantle from the lithosphere to a depth of 300 km. The density structure reveals the undulation of the lithosphere-asthenosphere boundary according to the distribution of density anomalies in the southwestern part of the South China Block. Our results suggest that the high-density lithospheric material is removed in the central area of Guangxi and the low-density asthenospheric material upwells in the south, replacing the delaminated lithospheric roots and penetrating them upwards into the crust, and consequently forming the granite exposed at the surface. With the characteristics of the basement and the terrestrial margin source of detrital zircons, we infer that the suture zone of the Yangtze and Cathaysian blocks in the southwestern South China block ( Guangxi section ) is along the Fuchuan-Wuxuan-Long 'an-Pingxiang line.

关 键 词：华南陆块西南缘 上地幔顶部 密度结构 三维重力反演 

分 类 号：P312[天文地球—固体地球物理学]