Incorporation of Faulted-bound Plates into Three Dimensional Models of Mantle Flow

Shijie Zhong and Michael Gurnis

Seismological Laboratory, 252-21, California Institute of Technology, Pasadena, CA 91125

January 11, 1996

Submitted to Nature

According to the theory of plate tectonics, plates are bounded by major tectonic faults; plate motion is nearly rigid with negligible internal strain and is approximately equally partitioned between poloidal and toroidal velocities. However, models of mantle flow with viscous rheology in an intact medium predict little toroidal component and substantial internal strain in surface motion. It has been suggested that the characteristics of plate motion are related to faulted plate margins which are observed to be weak. This has been confirmed by three dimensional models of mantle flow that incorporate faults and slab pull and ridge push forces. The models with weak faults yield surface motion characterized by little internal strain, significant toroidal motion, and sharp strike slip motion. Weak transform faults and their strong surroundings due to the non-Newtonian rheology cause transform faults to guide plate motion. The guiding effects of transform faults and the decoupling of thrust faults may result in oblique subduction.