Angle of subduction

Abstract

Plate tectonics is well established as an empirical description for modification of the Earth's outermost solid layer, although the dynamics of the plates are poorly understood. One view is that the plates are surface manifestations of the deep mantle convection which must inevitably occur if there are deepseated energy sources. Mantle convection, however, may not be an efficient driver of plate motions, and the negative buoyancy of subducting slabs may be more important. We consider here a simple fluid dynamical model which illustrates some of the general principles of subduction dynamics, and suggest an explanation for the observed subduction angle (the angle between the subducting slab and the Earth's surface). The model depends on the concept of a 'critical' negative buoyancy that plate material must attain before it can undergo steady-state subduction.