塔里木盆地南部上地幔各向异性研究

塔里木南缘位于塔里木块体同青藏高原碰撞的前缘,是认识青藏高原同周围块体相互作用的重要位置.横波分裂方法可以获得岩石圈及软流圈地幔的介质各向异性特征,进而探讨岩石圈变形和地幔流动.本文利用横波分裂方法对中国科学院地质与地球物理研究所、北京大学和南方科技大学联合布设在塔里木盆地南部的8个宽频带流动地震台站记录的SKS和SKKS震相进行分析,获得了塔里木盆地南部上地幔各向异性参数.分析结果显示,研究区快波偏振方向总体比较一致呈近东西向,但存在盆地边缘到盆地内部变化,而慢波延迟时间分布在0.3~1.5 s,差异较大.综合前人对青藏高原北缘和阿尔金断裂周边的横波分裂研究结果,研究区内大部分地区地幔流动方向和绝对板块运动方向保持一致,推测青藏高原北缘同塔里木盆地接触带,青藏高原北缘软流圈南东东向流动对塔里木块体下方地幔流动造成扰动,随着深入到塔里木块体内部,干扰越来越弱;同时青藏高原北部软流圈物质可能对塔里木盆地岩石圈产生影响,随着地幔软流圈物质持续向北运动逐渐冷却,对盆地内部岩石圈的影响程度减弱.

Upper mantle anisotropy analysis around the southern Tarim basin

The southern margin of Tarim,the front edge of the collision between the Tarim block and the Qinghai-Tibet Plateau,is an important place for understanding the interaction between the Qinghai-Tibet Plateau and surrounding blocks.The shear wave splitting method can obtain the media anisotropy characteristics of the lithospheric and asthenospheric mantle,and study of the lithosphere deformation and mantle flow.In this paper,we use the shear wave splitting method to analyze the SKS and SKKS phases recorded by eight broadband portable seismic stations jointly deployed by the Institute of Geology and Geophysics of the Chinese Academy of Sciences,Peking University and Southern University of Science and Technology in the southern Tarim Basin,and obtains anisotropy parameters in the upper mantle.The results show that the fast-wave polarization direction in the study area is generally consistent and nearly east-west,but there is a variation from the edge of the basin to the middle of the basin,and the delay time is about 0.3 to 1.5 s,and the difference is relatively large.Based on previous studies of shear wave splitting on the northern margin of the Qinghai-Tibet Plateau and around the Altyn Fault,most areas in the study area have the same direction of mantle flow and absolute plate movement.The SEE flow of the marginal asthenosphere disturbs the mantle flow under the Tarim block,and as it enters the Tarim block,the interference becomes weaker and weaker.At the same time,asthenosphere materials in the northern Qinghai-Tibet Plateau may affect the lithosphere of the Tarim Basin.As the mantle material continues to move northward,it gradually cools,and its influence on the inner lithosphere of the basin becomes weaker.