Abstract
The subduction interface material affects interface viscosity and slab buoyancy, two factors that play an important role in controlling subduction rates, slab shapes, and upper plate stresses. One component of the interface material is the mafic oceanic crust, which undergoes eclogitization at depth. Eclogitization increases both the interface viscosity and density, two effects that compete to control the effective slab pull and subduction velocities. The density increase from eclogitization and its impact on the subductability of oceanic plateaus has been studied, as has how viscosity variations associated with sediment-rich vs. sediment-starved subduction zones affect plate speeds. However, how the two competing effects interact in a dynamic subduction system has not been explored. In this study, we utilize the ASPECT finite element code to construct 2D subduction models. We incorporate a crustal layer with adjustable properties and the models evolve dynamically without external forces or velocities applied. The model domain is a 5120 X 2048 km box, with a higher resolution at the subduction interface (500 m grid spacing relative to 2 km elsewhere). We use a quartz dislocation creep flow law for the background subduction interface and an eclogite dislocation creep flow law for mafic oceanic crust on the interface. We vary a) oceanic crustal thickness (10-25km), b) eclogite effective viscosity (1019-1021 Pa.s), and c) eclogite density (3300-3500 kg/m3) and identify the parameter space over which subduction proceeds vs. that within which it is jammed. Consistent with prior research, our findings indicate that the density increase associated with eclogitization facilitates subduction, while the associated viscosity increase poses a hindrance. Our initial results indictate that, for an average interface viscosity of 1-7x1019 Pa.s, the promoting influence of the density increase outweighs the impact of increased viscosity, for an eclogite density greater than 3300 kg/m3, resulting in sustatined subduction. For higher interface viscosities, subduction jamming occurs. In summary, our study reveals that the incorporation of eclogitization leads to a slight enhancement in subduction velocity when the combined effects of viscosity and density changes are incorporated.