南海重力异常特征及其显著的构造意义

在南海地区地震测深数据有限的情况下,利用重力异常可以研究南海大范围的深部地壳结构及地质构造展布特征。基于空间重力异常,结合最新的地形、沉积物厚度及地震测深等数据,分别从地震约束的莫霍面反演和无约束的三维相关成像两个视角研究南海的地壳结构,利用壳幔界面起伏、地壳厚度及三维等效密度分布来探讨地壳结构的纵横向变化。同时,联合采用延拓、水平梯度及线性构造增强滤波方法聚焦重力异常中的区域线性特征,突出显示了反映地壳横向变化的深断裂、洋陆转换边界、海盆扩张轴等线性构造的展布。重力解释与贯穿南海南北的广州-巴拉望地学断面对比表明,重力异常反演及异常的区域线性特征,较好地揭示了南海海域大范围的地壳结构与区域构造展布。

Characteristics of Gravity Anomalies in the South China Sea and Their Tectonic Implications

Gravity anomalies can be used to infer the deep crustal structure in the South China Sea(SCS) where seismic data are limited to some specific points or profiles.This paper presents a comprehensive study of crustal structure by using gravity inversion for interface with seismic data constraints to invert depth of the Moho and to calculate crustal thickness,and by performing gravity anomalies correlative imaging method without constraints to construct the 3D subsurface distribution of equivalent density in the South China Sea.We also focus on the regional linear features of gravity anomalies and jointly use the continuation,horizontal gradient and linear feature enhancement filter to highlight the linear tectonics which always involve the density changes in horizontal,such as major deep faults,boundary of continental-oceanic crust,spreading axes of oceanic basin.The integrated geophysical analysis along the Guangzhou-Palawan geosciences transect demonstrates that the characteristics of the gravity anomalies and their inversion results allow us to reveal crustal structure and regional tectonics features in the large scale of the South China Sea.