俯冲带的负浮力及其影响因素

基于Ｍｕｒｎａｇｈａｎ－Ｂｉｒｃｈ状态方程，计算了密度Ｐ、热膨胀系数ａｖ、定压比热ｃｐ等物性参数在上地幔温压条件下的分布，给出了热传导系数ｋ在上地幔温压条件下的分布．采用准动力学计算方案，用有限元方法计算了板块不同俯冲速度、角度、不同厚度及不同俯冲深度情况下俯冲带的温度分布和密度分布．计算了不同俯冲模型下俯冲带的负浮力及其对岩石层板块形成的等效应力，发现负浮力在俯冲过程中是变化的，俯冲速度和板块厚度对其有明显的影响，在稳定俯冲状态，负浮力约为（１．５－２．３）×１０^１３Ｎｍ^－１，等效张应力约为０．２５－０．２９Ｇｐａ．

THE NEGATIVE BUOYANCY OF THE SUBDUCTION ZONE AND ITS AFFECTING FACTORS

The physical parameters ρ, αv, cp of the typical material in upper mantle were calculated using the Murnaghan-Birch state equation for upper mantle condition. On the basis of the quasldynamic computational scheme, the temperature distribution and the density distribution in the subduction zone for different subducting velocities and angles and different thicknesses of the subduction plate at different subducting depths were calculated using the F. E. M. The negative buoyancy on the subduction zone for different subduction models and the effective stress acting on the lithospheric plate were calculated by the numerical methods.It was found that the negative buoyancy is varied during the subducting process and the subducting velocity and the slab thickness have obvious effect on it. On the stable subducting state, the negative buoyancy is about （1. 5-2.3）×10¹³ Nm^-1, the effective tension stress is about 0. 25-0. 29 GPa.