摘要
为探究印度—欧亚大陆沿雅鲁藏布江缝合带(Yarlung-Zangbo suture zone,IYS)的接触关系及深部地球动力学过程,本研究在西藏墨脱县背崩乡附近横跨墨脱断裂带布设了一条长约20 km的高分辨率大地电磁测深(magnetotelluric,MT)剖面.背崩MT剖面精细揭示了主碰撞带的内部结构:(1)墨脱断裂带浅部(<5 km)表现为向深部收敛的负花状构造,指示其具有显著的走滑断裂特征;(2)断裂带内仍保存着印度板块沿IYS向拉萨地块之下俯冲的痕迹,且喜马拉雅东构造结附近可能发育印度上地壳的后展式顶板逆冲推覆构造;(3)与拉萨地体平均约30 km厚的上地壳(高阻)相比,墨脱地区上地壳显著减薄,暗示该区可能未经历藏南区域完整的碰撞演化过程,从而保留了大陆早期碰撞阶段的地质特征;(4)断裂带中地壳存在高导电异常体,推测系拉萨地体部分熔融物质向南运移并沿缝合带抬升所致.本研究为理解喜马拉雅东构造结的深部构造格局提供了新证据.
To elucidate the contact relationship between Indian and Eurasian plates along the Yarlung-Zangbo suture zone(IYS)and associated geodynamic processes,we acquired a high-resolution magnetotelluric(MT)profile extending 20 km across the Motuo fault zone near Beibeng Township,Motuo County,eastern Xizang.This NWSE oriented transect employed 30 MT stations with approximately 300-m spacing,covering frequency bands of 10000–0.0001 Hz to resolve crustal structure down to 30 km depth.Key findings from the electrical resistivity model reveal:(1)At shallow crustal levels(<5 km depth),the Motuo fault system exhibits a negative flower structure characterized by downward-converging conductive shear zones,diagnostic of dominant strike-slip deformation.(2)Preservation of Indian slab subduction traces beneath the Lhasa Block along the IYS,with possible development of a pop-up structure in the Indian upper crust near the eastern Himalayan syntaxis.(3)The resistive Lhasa Terrane upper crust is~20 km thick–33%thinner than the 30-km average in southern Xizang.This disparity implies either:(i)incomplete syn-collisional crustal shortening due to strain partitioning into strike-slip faults,or(ii)absence of crustal growth episodes that thickened the Lhasa Terrane.(4)A mid-crustal conductor at 15–30 km depth aligns with the suture zone.Its upward-flaring geometry indicates southward migration of melts from the Lhasa lower crust,which is facilitated by transpressional uplift along the IYS.These results demonstrate that the Motuo fault system operates as a crustal-scale transfer zone,where strike-slip kinematics preserve early collisional features while enabling melt migration through reactivated suture structures.The integrated model provides new constraints on strain accommodation mechanisms during continental indentation.
作者
王刚
方慧
裴发根
肖都
张小博
张耀阳
彭炎
白大为
乔汉青
张翔
常小鹏
葛欣旺
野柳帅
Wang Gang;Fang Hui;Pei Fagen;Xiao Du;Zhang Xiaobo;Zhang Yaoyang;Peng Yan;Bai Dawei;Qiao Hanqing;Zhang Xiang;Chang Xiaopeng;Ge Xinwang;Ye Liushuai(State Key Laboratory of Deep Earth Exploration and Imaging,Institute of Geophysical and Geochemical Exploration,CAGS,Tianjin 300300,China;State Key Laboratory for Deep Earth and Mineral Exploration,Institute of Geophysical and Geochemical Exploration,CAGS,Tianjin 300300,China;Key Laboratory of Geophysical Electromagnetic Probing Technologies of Ministry of Natural Resources,Tianjin 300300,China;Geophysical Survey Center of China Geological Survey,Tianjin 300300,China)
出处
《地球与行星物理论评(中英文)》
2025年第6期699-709,共11页
Reviews of Geophysics and Planetary Physics
基金
中国地质调查局地质调查资助项目(DD20250102801,DD20240101902)
华北—东北大地电磁子网一期(2024ZD1000203-06)
国家自然科学基金资助项目(41804075)。
