Seismically-induced rock damage along ultra-slow spreading ridges: consequences for serpentinization

Recent studies have recorded numerous small earthquakes in the rock volume surrounding mid-oceanic ridges, where serpentinization occurs. Sustained serpentinization of peridotite within the oceanic lithosphere requires an effective supply of water to rockss that experience continuous expansion of the solid volume due to hydration reactions. Hence, serpentinization preferentially occurs along ridge axes and in subduction zones where tectonic activity is intense and fracturing helps generate and sustain the permeability required to connect the near-seafloor environments to greater depth. Using earthquake catalogues based on ocean bottom seismic data acquired at two locations along the ultra-slow South-West Indian Ridge, we estimate the volume of oceanic crust affected by seismicity. The volume of damaged rock produced by earthquake activity is calculated using basic earthquake scaling laws and the observed earthquake catalogues. Our results show contrasting results for different ridge regimes. In ridge sections experiencing intense magmatic and volcanic activity, seismic activity and associated damage are too low to produce significant fracturing. Conversely, earthquake activity produced in the least magmatic regions generates sufficient rock damage and fracturing to sustain permeability and reactive surface area at depth, within the stability field of serpentine. These regions are inferred to provide a favorable environment for pervasive serpentinization.