关键词: 马里亚纳海沟-岛弧-海槽系统, Challenger Deep, 流变学, 重力异常, 俯冲弯曲与撕裂

Abstract: 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.

Key words: the Mariana trench-arc-trough system, the Challenger Deep, rheology, the free air gravity anomaly, subduction bending and tearing