The work proposed is to develop quantitative tools to model fluid flow and magmatism at subduction zones. The focus of the work will be on the top of the downgoing slab where fluids are released by metamorphic dehydration reactions, and the mantle wedge where fluids interact with high temperature solids to form magma. The work will start with 2-D models and extend to more challenging 3-D models.
Broader Impacts This project will contribute to the modeling infrastructure of the marine geology and geophysics community and other communities as well. It will also address the need for the synthesis of geochemical and geophysical observations as the MARGINS program enters its final stages. Finally, it will support a full-time post-doc.
Subduction zones such as in the Pacific Northwest or Japan are the locus of most of the planet’s largest earthquakes, volcanoes and tsunamis and are of great interest to scientists, engineers and policy makers who need to understand the dynamics and behaviors of these complex Earth systems. An important, but poorly understood component of the subduction system is the roles of fluids and magmas (partially molten rock) in controlling the behavior of volcanism, earthquakes and large-scale plate tectonics. To develop a better understanding of the coupled fluid/solid dynamics of subduction zones, this project developed a new computational modeling framework, TerraFERMA (the Transparent Finite Element Rapid Model Assembler, or TF) that allows users to rapidly construct and explore advanced computational models of coupled "multi-physics" problems where interactions between fluids/solids and energy transfer can lead to novel new physical behavior. TerraFERMA leverages several advanced open-source computational libraries (FEniCS/PETSc/SPuD) but makes these libraries more accessible by helping users rapidly create and explore custom applications from a common, human readable, options file that contains all the scientific and computational options required for efficient solution of complex coupled models. Because all options are exposed, these models are much more transparent, reproducible and can readily be shared and modified by a community of users. TF has been extensively tested against a large number of published benchmarks, is open-source and is scheduled for release sometime in summer 2013. This project has also used TerraFERMA to begin exploring the role of fluid release and transport from the slab through the wedge in subduction zones with an emphasis on understanding the role of permeability and solid rheology (the physical response of materials to being placed under stress, e.g. brittle, elastic or viscous response to stress) on the pathways and efficiency of fluid flow in subduction zones. A key observations which remains to be explained, is that the location of the primary volcanic arc in subduction zones is always ~100±40 km above the Earthquakes in the down going slab, independent of most parameters such as the age of the downgoing plate. Initial results of our models suggest that allowing the fluids to interact with the varying thermally controlled viscosity and flow structure of the slab and convecting wedge can lead to robust focusing of fluids towards the arc corner whereas simply assuming fluids migrate vertically due to buoyancy produces distributed fluid flow with little melting. Further work is required to understand the two-way coupling between fluid flow, melting and solid flow as well as the interactions of fluids with shallower earthquake processes, however, the inherent flexibility of TerraFERMA is designed to directly address these problems. Beyond modeling for subduction zones and their attendant natural hazards, TF provides a general, open-source modeling framework for many coupled problems arising in science and engineering that can be described using finite elements as well as providing a useful educational tool for teaching and exploring modeling of complex systems.
