华南大陆地壳结构和物质组成的接收函数与重力联合反演研究及构造含义

The nature of two tectonic units (Yangtze and Cathaysia blocks) and their division in South China are one of the key scientific questions for understanding tectonic evolution and geodynamics in this region, and have been debated for decades. In this research, we develop the technique of joint inversion of receiver function and gravity data for estimating crustal thickness and Poisson’s ratio, the technique for density interface inversion based on the algorithm of likelihood estimation, and the technique for constrained inversion of basement interface based on the horizontally variable density model, benefiting in decreasing ambiguities and enhancing precision and efficiency. We then utilize these techniques to obtain reliable parameters of crustal thickness, Poisson’s ratio, basement depth, and apparent density in South China, and subsequently analyze the relationship between Poisson’s ratio, crustal thickness, and apparent density. Then, with constraints of the geological data and the latest deep seismic reflection profile in South China detected by SinoProbe-02 project, we analyze the differences of crustal structure and composition between Yangtze and Cathaysia blocks revealed from these four crustal parameters, discuss their tectonic implications, and trace the spatial distribution of the collision zone between the two blocks. This research will provide important evidences for promoting the understanding and division of tectonic units in South China, and will provide technique support for revealing crustal structure and composition.

华南大陆两大构造单元（扬子与华夏）性质与划分是华南构造演化与动力学研究的关键科学问题之一，也是长期争论的焦点。本项目研发接收函数与重力联合反演地壳厚度与泊松比的技术，及其约束下的基于似然估计法的密度界面反演技术和基于横向变密度模型的基底面约束反演技术，降低反演的不确定性，提高反演精度和效率。然后应用这些技术获取华南大陆区域地壳厚度、泊松比、基底深度和视密度分布，分析泊松比与地壳厚度、视密度的相关性及构造含义。进一步，以地质资料和SinoPorbe-02项目探测的华南大陆深反射地震剖面为约束，剖析两大构造单元地壳结构与物质组成的差异性及其深部构造含义，追踪两大单元拼合带的空间展布。本项目研究为促进华南大陆大地构造单元认识和划分提供重要的深部制约，为揭露区域地壳结构与物质组成提供技术支撑。

华南大陆是由扬子与华夏两大块体新元古代沿江南造山带碰撞拼合而成的，两块体的拼合带东段普遍被认为沿绍兴-江山-萍乡断裂带一线，但拼合带西延长期争议不断，至今不清楚。针对这个重要科学问题，本项目研发接收函数与重力联合反演、密度界面反演、视密度填图和重磁频率域三维成像等技术，利用华南固定地震台站波形数据和区域重力异常数据，通过处理和反演获得了高质量的华南大陆地壳厚度、泊松比、基底深度和视密度分布，进而取得以下主要构造认识：（1）地壳厚度在华南西北侧偏大（38~46.5km）而东南侧偏小（26~34km），宜昌-吉首-百色沿线呈现北北东走向的地壳厚度梯级带，莫霍面向东陡升近4km，反映中生代岩石圈和地壳减薄自东向西延伸到宜昌-吉首-百色一线；（2）地壳泊松比在华南北部较高（0.28~0.31），反映地壳铁镁质矿物含量稍高，东南沿海地区中等（0.26~0.29），反映地壳铁镁质矿物含量和石英矿物含量相当，江南造山带和南部沿海地区明显低值（0.20~0.24），反映地壳石英矿物含量很高，其他地区稍低（0.22~0.26），反映地壳石英矿物含量稍高；（3）结合区域地质和最新深反射地震剖面解释，认为上述地壳泊松比的鲜明低值带可能代表扬子与华夏两大块体新元古代拼合带，其南界沿绍兴-江山-萍乡-永州-贵港-北海一线展布，北界沿石台-九江-益阳-吉首-百色一线展布。本项目成果为促进华南大陆深部构造和演化研究提供重要的深部制约，为揭露区域地壳结构与物质组成提供技术支撑。