Textural Analyses of Naturally Deformed Peridotite and Gabbro: Implications for the Interpretation of Geophysical Data and the Rheology of the Lithosphere

Woods Hole Oceanographic Institution, Woods Hole MA

Investigators

Abstract

EAR-0230267 Hirth The investigators will use their newly acquired electron backscatter diffraction (EBSD) system to measure lattice preferred orientations (LPO) and analyze microstructures in naturally deformed peridotites and gabbros. The increased efficiency in the measurement of crystal orientations made possible by the EBSD technique, particularly for minerals with low symmetry such as plagioclase and clinopyroxene, makes it a powerful tool to investigate rheological processes in both experimentally and naturally deformed rocks. The investigators will concentrate on the analysis of microstructures preserved in naturally deformed rocks with well-constrained deformation histories. This research will improve our understanding of the processes that control the rheology of both the lower crust and upper mantle. Specific projects include: (1) Determining the evolution of LPO with increasing strain in peridotite, concentrating on the influence of dynamic recrystallization, the effect of pyroxene content and the role of melt. The results of this project will provide constraints on the interpretation of seismic anisotropy in the mantle. (2) Using LPOs and grain size analyses to investigate conditions where a transition from dislocation creep to diffusion creep occurs under geologic conditions, and the possible role this process has in strain localization. The results of this part of the project will provide constraints on the mechanisms responsible for weakening lithospheric-scale fault zones at plate boundaries (3) Combining measurement of LPO with microstructural studies on oceanic gabbros to constrain the viscosity of lower crustal rocks under geologic conditions.