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Seismic controls on the progress of serpentinization at ultra-slow spreading ridges
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  • Claire Aupart,
  • Vera Schlindwein,
  • Yehuda Ben-Zion,
  • François Renard,
  • Bjorn Jamtveit
Claire Aupart
Physics of Geological Processes (PGP), The Njord Centre, Dept. of Geosciences, Unitversity of Oslo

Corresponding Author:c.o.m.aupart@geo.uio.no

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Vera Schlindwein
Alfred Wegener Institute for Polar and Marine Research
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Yehuda Ben-Zion
University of Southern California
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François Renard
University of Oslo
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Bjorn Jamtveit
University of Oslo
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Abstract

Sustained serpentinization of peridotite within the oceanic lithosphere requires effective supply of water to systems that experience continuous expansion of the solid volume. Hence, serpentinization preferentially occurs along ridge axes and in subduction zones where tectonic activity is intense and fracturing helps generating and sustaining the permeability required to connect seafloor-near environments to depth. The slowest mid-oceanic ridges produce little melt leading to discontinuous magmatic activity with very thin to no crust along most of the ridge length and up to 8 km thick crust focused around local magmatic centers. Three types of ultra-slow ridge sections can be distinguished: i) amagmatic, characterized by scarce basaltic crust and deep seismic activity, ii) magmatic, characterized by a thin basaltic crust and intermediate depth seismic activity, and iii) volcanic, characterized by a thick basaltic crust and shallow seismic activity. At amagmatic and magmatic ridge types, aseismic zones are identified above the seismic zone. The lower limit of the aseismic zone along amagmatic sections is thermally controlled and follows a 400-500˚C isotherm corresponding to the upper temperature limit for the onset of serpentinization. This observation suggests that the aseismic zone is significantly serpentinized with ample supply of water to the peridotite-serpentine interface. Based on recorded seismic activity, we estimate the associated rock volume affected by brittle damage for the different ultra-slow ridge types. We show that damage produced by seismic activity sustains pervasive serpentinization along amagmatic and magmatic types, while it is limited in the case of volcanic sections.