板块运动驱动力与稳定机制的研究

In order to know the plate tectonics better, it is necessary to study in details the forces that drive the plates to move and the dynamic mechanism that maintains the plate motion steady. A new model, the T22A model, for absolute plate motion is determined, constrained by the trends of globally distributed hotspot traces. This model not only provides better fit to the globally distributed hotpot data than the HS2-NUVEL1 model,but also implies that the return flow in the lower mantle has a velocity about 1/4 of the plate velocity. According to the theorem of angular momentum, a new approach, i.e., to compare the directions of the driving torques with those of the plate angular momentum, to study the driving forces of plate motion is presented, and new insights on the driving forces and stabilizing mechanism of plate motion are obtained as follows: the oceanic plate motions and the westward net rotation of the lithosphere are mainly driven by forces associated with subducting slabs; the continental plates are originally driven to move by ridge pushes, but their angular momentums tend to incline gradually to one of the principal axes of intertia tensor of the plates, in order to improve the kinematic stability; the variation of the dipping angle of the slabs, responding to the acceleration or deceleration of the plates, serves as a possible mechanism to stabilize the global plate motions. Under the joint constraints from the observed principal stress orientations and the VLBI data given by space geodesy, the global velocity field and stress field as well as the driving forces of plate motion are numerically inverted. The numerical results show that the forces associated with ridges and convergent boundaries are responsible for driving the plates to move, and indicate that the drag forces by the underlying mantle are resisting the plate motion.

利用最新的实测资料和板块运动模型，计算全球各板块的角动量以及各种板块作用力，根据角动量定量比较板块角动量与驱动力矩的方向，进而确定各板块的驱动力源，建立合理的岩石圈及软流圈流变学模型，数值模拟板块及俯冲板片在运动过程中受到扰动后的行为，定量分析板块运动的稳定性条件和维持稳定运动的动力学机制。