摘要
在青藏高原南缘有很多主动源和被动源地震学观测,为研究印度板块和欧亚大陆碰撞的过程和机制提供大量的地震学证据.由于印度板块的俯冲,青藏高原下方存在广泛分布的倾斜构造,对地壳结构成像带来挑战.本文基于改进的远震P波尾波自相关方法,获得了青藏高原Hi-CLIMB台阵下方清晰的P波反射率剖面.结果表明在拉萨地块下方,观察到类似于接收函数成像展示的“双Moho(doublets)”特征,反映了印度板块下地壳俯冲到青藏高原下方时可能发生了榴辉岩化;该特征向北可以追踪到31°N北侧附近,指示了印度板块下地壳的俯冲前缘.本文结果支持了印度板块向青藏高原俯冲过程中,其上地壳在雅鲁藏布江缝合带以南已被剥离,而其下地壳和岩石圈地幔继续向北俯冲并近水平地底侵到青藏高原下方.该P波反射率剖面还揭示了地壳内部的很多构造信息,例如:印度下地壳的减薄;雅鲁藏布江缝合带和班公湖—怒江缝合带的反射特征;拉萨地块和南羌塘地块的地壳内部分层特征;拉萨地块北侧和喜马拉雅北侧的中上地壳存在两个低速带.
Many active and passive seismic observations have been carried out in the southern Tibetan Plateau and provide substantial seismological evidences of the process and mechanism of the collision between the Indian plate and Eurasian continent.The subduction of the Indian plate produces widespread dipping structures beneath the Tibetan Plateau,which are complex and challenging for geophysical imaging.In this paper,we obtained a clear P-wave reflectivity profile beneath the Hi-CLIMB seismic array based on the improved teleseismic P wave coda autocorrelation(TsPCA)method.The results show a double Moho feature beneath the Lhasa Terrane,which is similar to receiver function results,indicating the eclogitization phenomenon that occurred when the Indian lower crust subducted below the Tibetan Plateau.The feature can be traced northward beyond 31°N,indicating the subduction front of the Indian lower crust.Our results support the hypothesis that the Indian plate subducted to the Tibetan Plateau,then the Indian upper crust was stripped off near the Yarlung Zangbo Suture(YZS),and the Indian lower crust and lithospheric mantle continued to subduct northward and almost horizontally underplating below the Tibetan Plateau.The P-wave reflectivity profile also reveals detailed interior structures of the crust,such as the thinning of Indian lower crust;the reflection features of the YZS and the Banggong-Nujiang Suture(BNS);the crust internal stratification features of the Lhasa Terrane and the Qiangtang Terrane;two low-velocity zones in the middle and upper crust of northern Himalaya and northern Lhasa Terrane.
作者
周进举
张伟
ZHOU JinJu;ZHANG Wei(School of Resources and Geoscience,China University of Mining and Science,Xuzhou Jiangsu 221116,China;Shenzhen Key Laboratory of Deep Offshore Oil and Gas Exploration Technology,Southern University of Science and Technology,Shenzhen Guangdong 518055,China;Guangdong Provincial Key Laboratory of Geophysical High-resolution Imaging Technology,Southern University of Science and Technology,Shenzhen Guangdong 518055,China;Department of Earth and Space Sciences,Southern University of Science and Technology,Shenzhen Guangdong 518055,China)
出处
《地球物理学报》
SCIE
EI
CAS
CSCD
北大核心
2023年第9期3662-3673,共12页
Chinese Journal of Geophysics
基金
国家自然科学基金项目(41904105,42074056)
江苏高校优势学科建设工程资助项目
广东省地球物理高精度成像技术重点实验室项目(2022B1212010002)
深圳市深远海油气勘探技术重点实验室项目(ZDSYS20190902093007855)
广东省重大人才工程引进类项目(2019QN01G801)资助。
