Deformation, CPO, and elastic anisotropy in low-grade metamorphic serpentinites, Atlantis Massif Oceanic Core Complex

Abstract

Crystallographic preferred orientation (CPO) and the associated seismic anisotropy of serpentinites are important factors for the understanding of tectonic settings involving hydrated Earth´s mantle, for example, at slow-spreading mid-ocean ridges. CPO of lizardite and magnetite in low-grade metamorphic serpentinites from the Atlantis Massif oceanic core complex (Mid-Atlantic Ridge, 30°N) were determined using synchrotron high energy X-ray diffraction in combination with Rietveld texture analysis. Serpentinite mesh structures show weak CPO while deformed samples show a single (0001) maximum perpendicular to the foliation. Seismic anisotropies calculated from CPO show up to >11% anisotropy for compressional waves (Vp) and shear wave splitting up to 0.38 km/s in the deformed samples. This indicates that deformation in shear zones controls elastic anisotropy and highlights its importance in defining the seismic signature of hydrated upper mantle.