基于融合重力异常的大别造山带东段莫霍面反演研究

Moho beneath the Eastern Dabie Orogen Insight from Inversion of Merged Gravity Anomaly

利用实测布格异常和EGM2008重力异常融合结果,采用频率域位场反演方法计算大别造山带东段莫霍面三维空间分布,结合区域地质构造和地震活动等资料讨论大别造山带东段莫霍面分布特征及其构造含义等。研究结果显示:(1)莫霍面空间分布体现了块体构造差异,大别造山带莫霍面最深,最大深度达42km,显示东大别造山带存在明显山根,扬子地块深度次之,华北地块最浅;郯庐断裂带及其东侧区域存在莫霍面上隆带;(2)大别造山带北侧和南侧莫霍面陡变带分别位于青山—晓天断裂附近和襄樊—广济断裂以北,体现华北地块和扬子地块向大别造山带之下俯冲的构造特征,指示了深部构造缝合带位置;莫霍面深度特征表明郯庐断裂带区域构造边界带属性明显,其切割深度至少达到壳幔边界,大别造山带商城—麻城断裂两侧经历了差异隆升;(3)研究区域绝大多数地震发生在莫霍面以上深度,莫霍面深度陡变带、上隆带及不同莫霍面深度特征区的转换带为区域地震活动提供了深部构造条件。

The gravity anomaly used in this study was obtained by merging EGM2008 gravity anomaly and observed gravity anomaly.The Moho depth beneath the eastern Dabie Orogen was obtained by frequency domain inversion of merged gravity anomaly.In combination with regional tectonic and seismic data,the Moho undulation and its tectonic implications were discussed.The results show that:(1) the depth of the Moho beneath the eastern Dabie Orogen reaches the maximum value of 42km,while the Moho depth of Yangtze block is intermediate,and the Moho of the North China block is the shallowest.This suggests that there exists a crustal root of the eastern Dabie Orogen and the Moho undulation reflects the tectonic features of different tectonic blocks.(2)Steep Moho gradients along the north and south margins of the eastern Dabie Orogen locate at Qingshan-Xiaotian fault and north of the Xiangfan-Guangji fault respectively,represent the subductions of the North China block and the Yangtze block beneath the Dabie Orogen,and indicate the locations of deep suture zones.The Moho undulation shows that the Tanlu fault zone is the boundary of different tectonic blocks,and has extended to crust-mantle boundary or more deep.Within the eastern Dabie Orogen,the west side and east side of Shangcheng-Macheng fault were uplifted out of sync.(3) The great majority of earthquakes in this region occurred above the Moho interface.Steep Moho gradient zones,the Moho uplifting zones and transition zones of different Moho undulation areas provide deep structural environments for seismic activities.