Manuel D. Menzel, Janos L Urai , Estibalitz Ukar, Alexander Schwedt, Greg Hirth, András Kovács, Lidia Kibkalo, Peter B. Kelemen

Carbonated serpentinites (listvenites) in the Oman Ophiolite record mineralization of several GT of CO2, but the mechanisms providing permeability for continued reactive fluid flow are unclear. Samples of the Oman Drilling Project show that listvenites with a penetrative foliation have abundant microstructures related to crystal growth and indicate that the carbonation reaction occurred during tectonic deformation. Folded magnesite (magnesium carbonate) veins mark the onset of carbonation, followed by deformation during growth of magnesite. Undeformed magnesite overgrowths and euhedral quartz growth zoning indicate that deformation stopped when the reaction was completed. We propose deformation by dilatant granular flow and dissolution-precipitation assisted the reaction, while deformation in turn was localized in the weak reacting mass. Lithostatic pore pressures promoted this process, creating dilatant porosity for CO2 transport and solid volume increase. This feedback mechanism may be common in subduction zones, allowing intense fluid-rock interaction in mantle rocks.