From peridotite to listvenite – perspectives on the processes, mechanisms and settings of ultramafic mineral carbonation to quartz-magnesite rocks

International audience ; Listvenites form by metasomatic transformation of variably serpentinized peridotites to carbonate-quartz rocks due to extensive reaction with CO$_2$-bearing aqueous fluids. This transformation sequesters large amounts of carbon since listvenites commonly contain >30 wt% CO$_2$. Although volumetrically a rare rock type, they occur in many ophiolites throughout much of the geological record, with preserved examples from the Archean to the present. Listvenites are highly interesting because they can form in the forearc mantle wedge, modulating deep carbon cycling. They further are natural analogues for optimal carbon sequestration by mineral carbonation.Here we elucidate the influence of different controlling variables and feedback mechanisms on natural listvenite formation, investigate which prerequisites and geodynamic settings are favorable, and discuss related implications for the deep carbon cycle and engineered CO2 storage by mineral carbonation. Using thermodynamic fluid infiltration-fractionation models that simulate idealized, step-wise carbonation flow-through experiments, we quantify expected changes in volume, mass, solute transfer (e.g. Mg, Si mobility), redox conditions and pH with reaction progress in dependence of protolith composition, infiltrated fluid composition, temperature and pressure. The models agree well with experiments and natural observations of high-T carbonation but have limitations at low temperature (T ≲ 130–150 °C) where kinetic effects in experiments limit the approach to equilibrium. Our modeling and assessment of typical CO$_2$ concentrations in metamorphic/hydrothermal fluids highlight that listvenite formation requires high time-integrated fluid flux, which in turn requires dynamic renewal of permeability despite reactive volume expansion. As most known listvenites crop out along tectonic contacts between crustal and ultramafic rocks in ophiolites that delineate major orogenic sutures, key factors controlling CO$_2$ supply are deviatoric stress and ...