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The interplay between brittle and ductile processes at oceanic transform faults

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Long sections of plate boundaries move by displacement on faults, which in the oceans includes transform faults and low angle detachment faults. Studies have long demonstrated that fluid circulation helps drive weakening and seismic failure in the shallow brittle zone of faults. In the oceanic lithosphere, fluid circulation is usually assumed to end when rocks transition from brittle failure to plastic flow. I will present new results that suggest that water circulates into the brittle-ductile zone on oceanic faults, through an alternating cycle of brittle fracture and ductile mylonitic deformation. Peridotite minerals react with water to form weaker hydrous phases, suggesting that hydration may be essential for localized deformation across the entire oceanic plate boundary.

Reference list: Behn, M. D., M. S. Boettcher, and G. Hirth (2007), Thermal structure of oceanic transform faults, Geol, 35(4), 307–310, doi:10.1130/G23112A.1.

McGuire, J. J., J. A. Collins, P. Gouédard, E. Roland, D. Lizarralde, M. S. Boettcher, M. D. Behn, and R. D. van der Hilst (2012), Variations in earthquake rupture properties along the Gofar transform fault, East Pacific Rise, Nature Geoscience, 5, 336–341, doi:10.1038/ngeo1454.

Warren, J. M., and G. Hirth (2006), Grain size sensitive deformation mechanisms in naturally deformed peridotites, Earth and Planetary Science Letters, 248(1-2), 438–450, doi:10.1016/j.epsl.2006.06.006.

This talk is part of the Department of Earth Sciences Seminars (downtown) series.

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