中国东南部P波速度结构与构造分析

P wave velocity structure and tectonic analysis beneath southeastern China

利用中国东南部地震台站的波形数据,通过远震P波层析成像方法反演了福建及台湾地区的上地幔P波速度结构,据此分析了华夏块体的构造属性并探讨了中国东南部上地幔的深部动力学机制.结果表明,研究区上地幔速度结构存在明显的横向非均匀性,它们与区域构造的深部动力学成因密切相关.宏观上,NE向展布的低速异常与东南沿海地区中新生代火成岩的条带状分布保持了较好的一致性,推测其上地幔可能存在幔源物质上涌;以政和—大埔断裂带为界,东、西华夏块体的速度结构存在差异,结合前人的研究结果分析,东、西华夏块体岩石圈减薄和中新生代岩浆活动的驱动机制有所不同,西华夏块体为“板块俯冲+岩浆底侵(岩石圈拆沉)”的动力学模式,东华夏块体是“玄武质岩浆迁移+岩浆底侵”的动力学模式.

Using waveform data of seismic stations in southeastern China,we employed the teleseismic P wave tomography method to invert the upper mantle P wave velocity structure beneath the Fujian-Taiwan region.Based on these results,we analyzed tectonic properties of the Cathaysia block and discussed deep dynamic mechanism of the upper mantle in southeastern China.The results show that the upper mantle velocity structure in this region is obviously lateral heterogeneity,which is closely related to deep dynamic conditions of its tectonic.Macroscopically seeing,the NE distribution of the low velocity structure is consist with the zonal distribution of Mesozoic-Cenozoic igneous rocks in coastal areas of southeastern China,and we speculate that mantle upwelling may occur beneath this region.The difference of velocity structures between the East and West Cathaysia blocks is observed in this study.Based on the former research,we suggest that the triggering mechanism is different for lithospheric thinning and Mesozoic-Cenozoic magmatic activities between them,the West Cathaysia block corresponding to the dynamic model“slab subduction+magma invasion(lithosphere delamination)”and the East Cathaysia block harmonizing with another dynamic model“migration of basaltic magma+magma invasion”.