青藏高原S波和泊松比的层析成像  

S wave velocity and Poisson's ratio tomography of the Tibetan Plateau

作　　者：瞿辰[1] 刘晓宇 于常青[1] 胥颐[3,4] 杨文采 QU Chen;LIU XiaoYu;YU ChangQing;XU Yi;YANG WenCai(Institute of Geology,Chinese Academy of Geological Sciences,Beijing 100037,China;School of Geophysics and Information Technology,China University of Geosciences(Beijing),Beijing 100083,China;Institute of Geology and Geophysics,Chinese Academy of Sciences,Beijing 100029,China;School of Earth Sciences,Zhejiang University,Hangzhou 310027,China)

机构地区：[1]中国地质科学院地质研究所,北京100037 [2]中国地质大学(北京)地球物理与信息技术学院,北京100083 [3]中国科学院地质与地球物理研究所,北京100029 [4]浙江大学地球科学学院,杭州310027

出　　处：《地球物理学报》2020年第10期3640-3652,共13页Chinese Journal of Geophysics

基　　金：中国地质调查局基础性公益性地质矿产调查(121201102000150014);中国地质科学院地质研究所基本科研业务费(J2007)资助.

摘　　要：本研究使用中国数字地震台网(CDSN)(2009—2016)走时数据开展青藏高原地壳地震波速度三维层析成像研究,获得分辨率达到1°×1°×20 km的青藏高原地壳S波三维速度结构和泊松比分布.结果表明,分布在可可西里和羌塘北部的高钾质和钾质火山岩带,其上地壳到下地壳都存在S波波速扰动负异常和高泊松比.说明第三纪青藏高原隆升过程中,由于大陆碰撞使三叠纪的东昆仑缝合带重新破裂,造成大量壳幔混合熔融物质上涌和火山喷发,进而揭示了青藏高原北部新生代火山岩的存在与青藏高原的形成和隆升密切相关;青藏高原新生代裂谷位于中下地壳S波速度扰动负异常带的两侧,裂谷带之下的中下地壳泊松比减小到0.22以下.裂谷带之下中下地壳的S波速异常分布和泊松比值可以推断青藏高原新生代裂谷深达中地壳底部,这个推论与密度扰动三维成像的相关结论一致.青藏高原S波速度和泊松比在下地壳至壳幔边界随深度产生急剧变化,说明地壳内部发生了大规模的层间拆离和水平剪切;青藏高原东构造结之下泊松比高达0.29~0.33,S波速度扰动为负异常,推断东构造结下方地壳主要由坚硬的蛇纹石化橄榄岩组成;青藏高原中下地壳S波速负异常区范围大面积扩大,地壳底部几乎被S波速低值区全部覆盖.下地壳S波异常分布特点可能反映下地壳管道流的影响.In this study,three-dimensional tomographic studies of crustal seismic wave velocity structure beneath the Tibetan Plateau were carried out using seismic travel time data from China Digital Seismograph Network(CDSN)(2009—2016)seismic stations.The three-dimensional S-wave velocity structure and Poisson's ratio distribution of the Tibetan Plateau with a resolution of 1°×1°×20 km were obtained.The results show that the negative anomalous zones of S-wave velocity and high Poisson's ratio zones could be found from the upper crust to the lower crust under the high-potassium and potash volcanic belts of Kekexili and northern Qiangtang.This indicates that during the Tertiary Tibetan Plateau uplift,the East Kunlun Triassic suture zone re-ruptured due to continental collisions,resulting the upwelling of massive crust-mantle mixed molten material and volcanic eruption.This further reveals that the existence of Cenozoic volcanic belts in the northern Tibetan Plateau is closely related to the formation and uplift of the Tibetan Plateau.The Cenozoic rift zones of the Tibetan Plateau are located at both sides of the S-wave velocity negative anomaly zones in middle-lower crust,the Poisson's ratio below the rift zones in middle-lower crust are less than 0.22.From the anomalous distribution of S-wave velocity and Poisson's ratio in middle-lower crust under the Cenozoic rift zones of Tibetan Plateau,it could be deduced that the Cenozoic rift of Tibetan Plateau had reached the bottom of the middle crust.This is consistent with the conclusions from the crustal density imaging study of the Tibetan Plateau using gravity inversion.The S-wave velocity and Poisson's ratio of the Tibetan Plateau change sharply with depth from lower crust to crust-mantle boundary,which indicates that large-scale interlayer detachment and horizontal shear occurred in the crust.The Poisson's ratio of the eastern tectonic syntaxis in the Tibetan Plateau is as high as 0.29~0.33,and the S-wave velocity perturbation under eastern tectonic syntaxis is negati

关 键 词：青藏高原 地震S波 泊松比 三维层析成像 火山岩带 地壳拆离 新生代裂谷 东构造结 

分 类 号：P315[天文地球—地震学]