Volatiles and melting: Advanced models of fluid flow in subduction systems

Geodynamic models that incorporate theoretical and experimental constraints are critical for synthesizing the disparate geophysical and geochemical observations from subduction zones. Their application allows for quantitative inferences about the properties and processes occurring at these complex plate boundaries. Considerable work has developed high-resolution solid flow and thermal models for subduction zones, but there has been considerably less modeling of the explicit flow of hydrous fluids and magmas through the slab and wedge. Because many of the critical observations, particularly those of geochemistry, depend on the sources and pathways of fluids; considerable questions remain as how to relate these observations to the underlying dynamics. We present new models for calculating and exploring the generation and flow of fluids in subduction zones. Key features of these models include the ability to reuse existing high-resolution thermal/solid flow models on unstructured grids that can be generated for specific arc geometries, together with thermodynamic calculations of phase diagrams that can be used to calculate the rate and distribution of fluid production in the slab. Given these inputs, the models solve for the explicit flow of fluid using the magma-dynamics formulation of McKenzie (1984). The first generation of models address where and at what rates fluids are generated in the slab and explore the consequences of physical parameters such as permeability and solid rheology for affecting the potential fluid-flow paths through the slab and wedge. In particular, initial results suggest that flow paths are particularly sensitive to mantle rheology, with the possibility of considerable up- dip slab flow if the slabs are relatively strong.