海沟后退对地幔对流的影响

本文分析了有海底扩张无海沟后退、有海沟后退无海底扩张以及海底扩张与海沟后退共存等３种情况下，俯冲板片运动与海沟迁移的关系．用幂律流体有限元方法计算海沟后退对地幔对流的影响．地幔有效粘度除依赖应力偏张量的第二不变量以外，尚与温度、压力（含流体静压力和流动压力）有关．计算表明，对流环、高流动负压区以及低粘区的个数和位置，均受控于海沟是否后退以及海底是否扩张；温度场与海沟后退无明显关系．流动压力对形成洋中脊和弧后火山、驱动地幔对流以及维持板片的倾斜角度都具有重要意义．

THE INFLUENCE OF TRENCH RETROGRADATION ON MANTLE CONVECTION

An analysis of the relation between the trench motion and the slab motion for three cases that:with the seafloor spreading without the trench retrogradation;with the trench retrogradation without the seafloor spreading;with both the seafloor spreading and the trench retrogradation have been carried out.A power law fluid whose rheological property depends on the temperature and total pressure which includs a static pressure and a kinematic pressure as well as on the 2nd invariant of deviatoric tensor of stress or strain rate have been used to investigate various fields of mantie flow either with or without the trench retrogradation by means of 2-D finite element method.The computing results show that there are remarkable influence of the trench retrogradation on me velocity field,the kinematic pressure field and the viscosity field but the small influence on the temperature field.The number and position of convection calls,lower viscosity areas and higher negative pressure areas are controlled by whether the trench retrogradation or not and whether the seafloor spreading or not. The kinematic pressure is significant for forming the oceanic ridge and the back-arc volcano,driving mantle convection.