汤加俯冲带上地幔剪切波速度和方位各向异性结构  

Shear-wave Velocity and Azimuthal Anisotropy in the Upper Mantle of the Tonga Subduction Zone

作　　者：赵迪 刘鑫[1] 赵大鹏[2] ZHAO Di;LIU Xin;ZHAO Dapeng(College of Marine Geosciences,Ocean University of China,Qingdao,Shandong 266100,China;Department of Geophysics,Graduate School of Science,Tohoku University,Sendai 980-8578,Japan)

机构地区：[1]中国海洋大学海洋地球科学学院,山东青岛266100 [2]日本东北大学理学部地球物理系,日本仙台980857

出　　处：《现代地质》2025年第1期1-17,共17页Geoscience

基　　金：国家自然科学基金面上项目(41972211);日本科学促进协会项目(19H01996)。

摘　　要：位于西南太平洋的汤加俯冲带发育有世界上最典型的“沟-弧-盆”体系,该区域不仅具有全球最快的板块俯冲速度,还发育扩张速率最快的弧后盆地——劳盆地。汤加俯冲带东北侧的萨摩亚地幔柱也与该俯冲系统间存在着强烈的相互作用,这使得该区的地幔动力过程更加复杂。虽然前人已在此进行了许多地球物理研究,但汤加俯冲带上地幔的精细三维结构,尤其是各向异性结构特征仍不清晰。为此,本文利用20~150 s周期范围内的远震基阶瑞利波的振幅和相位数据开展了方位各向异性层析成像研究,以期进一步约束汤加地区上地幔速度结构。研究结果认为:(1)萨摩亚地幔柱物质向南流入劳盆地主要发生在小于50 km的深度范围内;(2)劳盆地北部地幔楔中主要呈现东西向的地幔流动,而南部则存在南北向的地幔流动,这可能是地幔物质被动流动以适应俯冲板块不对称回卷的结果;(3)俯冲板片内主要呈现近南北向的快波方向,这可能与俯冲相关的正断层有关;(4)海沟外侧软流圈中存在平行海沟的横向地幔流动,这可能是软流圈物质受俯冲板块回卷挤压产生的。The Tonga Subduction Zone,located in the southwestern Pacific,is characterized by the global most typical trench-arc-basin system.It not only has the fastest plate convergence rate globally but also features the fastest back-arc basin,the Lau Basin.The Samoan mantle plume,situated on the northeastern side of the Tonga Subduction Zone,interacts strongly with the subducting system,making the mantle dynamics in this region even more complex.Many previous geophysical investigations of the region have been conducted,but the fine three-dimensional structure of the upper mantle,especially its anisotropic structure,is still not very clear.Here we apply azimuthal anisotropy tomography using amplitude and phase data of teleseismic fundamental-mode Rayleigh waves at periods of 20-150 s to further constrain the upper mantle structure beneath Tonga.Our results show the following features:(1)The southward inflow of the Samoan mantle plume material into the Lau Basin mainly occurs at depths less than 50 km.(2)There is a west-east mantle flow beneath the northern part of the Lau Basin,while a south-north mantle flow exists beneath the southern part,possibly resulting from passive mantle flow to accommodate asymmetric rollback of the subducting slab.(3)Within the subducting slab,the fast-velocity direction is nearly north-south,possibly caused by the presence of subduction-related normal faults.(4)In the asthenosphere beneath the outer-rise region,there is a lateral mantle flow parallel to the trench,probably formed because the asthenospheric material being extruded by the rollback of the subducting slab.

关 键 词：各向异性层析成像 地幔对流 俯冲板片 汤加俯冲带 劳盆地 

分 类 号：P542.4[天文地球—构造地质学] P542.5[天文地球—地质学]