CAREER: Investigating the Relationship Between Mantle Shear Localization, Melt Flow and Water Content

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The occurrence of shear localization is one of the defining properties of plate tectonics, but the mechanisms driving shear localization are poorly constrained. Both melt and water have been proposed as agents that lead to ductile localization within the Earth?s mantle. This CAREER research project investigates the relationship between shear localization, melt flow and water through analysis of well-preserved shear zones in one of the best examples of mantle peridotite, the Josephine peridotite in Oregon. Terrestrial laser scanning will be used to map shear zones at high resolution, with the survey being carried out as part of an undergraduate field class. The survey results will be merged with GPS data on the location and orientation of shear zones and melt channels. Microstructural analysis of samples collected during fieldwork will be carried out to determine the relationship between mineral orientations and variations in melt and water contents. Analysis of water concentrations in peridotite pyroxenes will be used to constrain the outcrop-scale variation in water in relation to shear deformation. The education component of this CAREER project will provide undergraduate and graduate students with experience in advanced field methods through the use of terrestrial laser scanning. Experience with cutting-edge analytical techniques and field campaign planning will prepare students for future careers in the geosciences. Integration of teaching and research in this project will expose students to a variety of topics and techniques across a range of disciplines, including petrology, geochemistry, rock deformation, tectonics and seismology.The research in this proposal lies at the intersection of petrology, geochemistry, rock deformation, tectonics, and seismology. Project results will be widely applicable across disciplines. For example, the combination of microstructural analyses with peridotite geochemistry will provide insight into the factors that control seismic anisotropy. Results of this project will also be applicable to themes identified in the 2011 GeoPRISMS Implementation Plan, including (i) understanding mantle wedge dynamics; (ii) fore-arc to back-arc volatile fluxes and (iii) metamorphism, melting, and fluid/melt migration in the mantle wedge.