Numerical Modelling of Tectonic Flow behind Island Arcs

High heat flow in marginal basins and island arc volcanism are explained by numerical modelling of flow induced by the downgoing slab. The hypothesis that frictional heating above the slab causes thermal diapirs to rise is mechanically unfeasible since the region above the slab must be fluid enough to convect thermally, yet so viscous that the motion of the slab produces over 2 kilobars of stress. The calculation of induced flow is two-dimensional, time dependent, with a variable viscosity dependent on temperature and pressure. A yield stress was used to approximate fault dislocations. The calculation is very sensitive to the material properties and to localized flow near the base of the interface between the slab and the landward plate. The highest stress occurred at the base of the slab interface. This area ablated creating a narrow channel necessary for separating melt from mostly crystalline mush to establish a source of volcanic magmas. In the marginal basin area, tensile yielding occurred in the plate causing it to thin and raise the heat flow significantly. The yielding continued until a complete rift occurred. Induced flow is, then, a likely explanation for island arc volcanics and high heat flow in marginal basins.