华南地壳及壳幔过渡带泊松比及其地质意义

The Poisson’s ratio of the crust-mantle of South China and its geological significance

地震波泊松比蕴涵着丰富的地质信息,根据泊松比可以识别地壳岩石的基性程度,进而分析地球动力学与成矿背景。本文搜集整理了国家地震科学数据共享中心等数据平台自20世纪80年代至2017年底的天然地震震相资料,经过数据筛选,得到华南研究区内M≥2.0级地震事件11410个。通过最小二乘法拟合数据的走时-震中距关系直线方程,得到Pg波平均波速6.11 km/s, Sg波平均波速3.60 km/s,首波Pn波平均波速8.06 km/s, Sn波平均波速4.59 km/s。在此基础上,求得华南地壳平均波速比Vp/Vs为1.697,由公式计算得到华南地壳的平均泊松比为0.234,壳幔界面附近的平均波速比Vp/Vs为1.756,计算得到壳幔界面附近的平均泊松比为0.260。走时反演给出的泊松比结果显示扬子地块、华夏地块以及东南沿海地壳的物性差异。华夏地块与扬子地块之间存在大面积的低泊松比异常区,与江南造山带存在良好的对应关系;而东南沿海、钦杭成矿带泊松比明显较高,解释为幔源物质注入地壳的结果。

Poisson’s ratio contains rich geological information, the degree of basic lithology of crustal rock can be identified from the Poisson’s ratio, and thus it could be used to analyze geodynamics and metallogenic background. The seismic phase data of local natural earthquakes ranging from the 1980 s to the end of 2017 were collected from the data sharing platform such as China Earthquake Data Center in this study. Furthermore, 11410 earthquakes(M≥2.0) in South China were obtained through screening procedure. According to the linear equations of travel time-epicenter distance relation fitted by least square method, the average velocity of Pg-wave, Sg-wave, Pn-wave and Sn-wave were 6.11 km/s, 3.60 km/s, 8.06 km/s, and 4.59 km/s, respectively. The average velocity ratio(Vp/Vs) of the crust of South China was calculated to be 1.697 and its Poisson’s ratio was 0.234;In addition,the calculated average velocity ratio near the crust-mantle boundary of South China was 1.756 and its Poisson’s ratio was 0.260.The results of Poisson’s ratio using the travel-time tomography method show the petrologic differences among the Yangtze block,Cathaysia Block, and Southeastern coast crust. The large low Poisson’s ratio area between the Yangtze block and Cathaysia Block is well correlated with the Jiangnan orogeny belt, and the relatively high Poisson’s ratio correlated with Qinhang metallogenic belt and Southeast coast are interpreted as underplating of the mantle derived magma.