Shear Zone Development in Serpentinized Mantle: Implications for the Strength of Oceanic Transform Faults

Oceanic transform faults display fewer and smaller-magnitude earthquakes than expected for their length. Several mechanisms have been inferred to explain this seismic slip deficit, including increased fault zone damage resulting in elevated fluid flow, the alteration of olivine serpentine. However, date, these possible are not supported by direct observation. We use micro kilometer scale observations from an exhumed oceanic Troodos Ophiolite, Cyprus, determine mineral-scale deformation infer likely controls on behavior serpentinized lithospheric mantle active faults. document a range fabrics massive, scaly phyllonitic serpentinite, attesting mixed brittle-ductile within serpentinite shear zones. The progressive development foliation, with cumulative strain, is efficient weakening mechanism serpentinite. Further promoted transition serpentine polytype lizardite-dominated massive serpentinites chrysotile-dominated foliation requires dissolution-precipitation processes. Discrete fractures locally crosscut, but also deformed by, foliated serpentinites. These brittle structures can be explained local transient strain rates, play crucial role localization providing positive feedback increasing permeability. propose that evolution structure style documented Southern Transform Fault Zone viable explanation dominantly creeping long-term weakness