马里亚纳海沟Challenger Deep的岩石圈流变结构与动力学分析

马里亚纳海沟是西太平洋板块边缘沟-弧-盆体系构造演化的关键地区，其南端的Challenger Deep不仅是地球表面最深点，也是马里亚纳海沟、马里亚纳岛弧、马里亚纳海槽、西马里亚纳洋脊和帕里西维拉海盆的构造汇聚点。开展岩石流变结构与动力学过程研究对于认识Challenger Deep的形成演化具有重要的科学意义。利用综合地球物理资料，通过对重、磁数据的计算分析，研究马里亚纳沟-弧-槽-盆系统的等效黏滞系数和岩石圈强度等流变学特征。利用地震资料，勾绘海沟之下贝尼奥夫带随深度变化的特征以及陡变形态。计算结果表明：对应马里亚纳海沟-岛弧-海槽系统，自由空气重力异常向东凸出，形成弧型异常区；区内异常表现为串珠状线性特征，异常值中间高，两侧低。不同深度岩石圈累积强度比值表明，海沟南北两侧地壳上硬下软，海沟中部地壳上软下硬。在给定应变速率条件下计算的等效黏滞系数东高西低，说明西侧构造体地壳比东侧构造体地壳更容易变形。Challenger Deep岩石圈强度较大，等效黏滞系数较高，具有上硬下软的流变学特征，为板块俯冲在该区的弯曲、撕裂与快速翻转提供了重要条件。地震与重力剖面分析表明，Challenger Deep处的岩石圈累积应力强度和有效粘滞系数条件，可以使马里亚纳海沟俯冲带在重力作用下弯曲、开裂，或部分向南翻转、变陡。

Analysis of lithospheric rheological structure and dynamics of the Challenger Deep in Mariana trench

Mariana trench is the key area of tectonic evolution in the western Pacific ocean plate edge trench-arc-basin system. The Challenger Deep in the southernmost Mariana trench is the deepest point on the Earth's surface, and the structural convergence point of Mariana trench, Mariana arc, Mariana trough, west Mariana ridge, and Parece Vela basin. It is important for understanding Challenger Deep formation evolution to study Challenger Deep lithospheric rheological structure and dynamics. In this work, based on the analysis of gravity and magnetic data, we obtained the rheological characteristics of the equivalent viscous coefficient and the lithosphere strength of the Mariana trench-arc-trough-basin system. We drew the characteristics changing with depth and the abrupt form of Wadati-Benioff zone under the trench through the calculation of the seismic data. The calculation results are showed as follows. 1) Corresponding to Mariana trench-arc-trough system, the free air gravity anomaly formed an eastward protruding arc anomaly zone, which showed beaded linear characteristics. The abnormal value was high in the middle and low at both sides. 2) The lithosphere integrated intensity ratios at different depths reflected that on the north and south sides of the trench the upper crust was hard and the lower was soft, and on the middle trench the upper crust was soft and the lower was hard. We calculated the equivalent viscosity coefficients using a given strain rate, and found that the value in the east was high and the value in the west was low, which illustrated that the deformation of the west side of the crust is more easily than that of the east side of the crust. With large lithosphere strength, high equivalent viscous coefficient, and hard upper crust and soft lower crust rheological characteristics, Challenger Deep provided important conditions for bending, tearing, and rapid reversal of the plate subduction area. The analysis of seismicity and gravity profile showed that the lithosphere cumulative stress intensity and effective viscosity coefficient at the Challenger Deep would make the Mariana trench subduction zone bending and cracking or partially turning toward the south and steeping under the action of gravity.