CSEDI Collaborative Research: Influence of Grain-Size Evolution on Global and Regional Mantle Flow and Upper Mantle Seismic Structure

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This award is funded under the American Recovery and Reinvestment Act of 2009 (Public Law 111-5)Although large-scale convection in the Earth?s mantle ultimately controls tectonic deformation at the Earth's surface, the link between deep mantle flow and plate tectonics remains poorly understood. This is because patterns of mantle flow are difficult to constrain from surface observations and are sensitive to variations in the material (or rheologic) properties that control rock deformation within the plate-mantle coupling zone known as the asthenosphere. The goal of this project is to use computer simulations to evaluate how the material properties of the Earth influence the style of mantle convection. This understanding is important because it will help us quantify the tectonic forces that control geologic deformation and its associated seismic hazard, particularly at plate boundaries where most major earthquakes and volcanic eruptions occur. The results of this project will be directly relevant to several NSF-sponsored programs such as Margins, Ridge2000, CSEDI, CIG, and Earthscope and will help fund graduate students at both WHOI and the University of Hawaii.In the Earth?s asthenosphere, mantle rheology depends on a variety of factors including temperature, pressure, water content, deformation mode, and grain-size, all of which depend on the time-dependent evolution of mantle flow. In this project, the investigators will examine the grain-size dependence of mantle rheology by computing grain-size evolution on a micro-scale (cm and smaller) within 3-D mantle flow models on regional (10s to 100s km) and global (100s to 1000s km) scales. They will accomplish this by incorporating laboratory-based models for grain-size evolution into large-scale mantle flow models to investigate the potential importance of feedbacks between grain-size, rock rheology, and flow. The predictions made by these numerical models will be constrained using seismic data (including variations in seismic anisotropy, wave speed, and attenuation) and rock texture analyses from a spectrum of tectonic environments. In doing so, they will improve our understanding of the relationship between mantle flow, surface tectonics, and grain size in the upper mantle.