Rates and mechanisms of element transfer during mineral reactions in the presence of a fluid phase

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The Earth is characterized by a high variance of element and isotope distribution with respect to space and time. The resulting dynamic system therefore requires substantial transport of heat and mass on very different scales (from single atoms to several hundreds of kilometers), which are typically driven by disequilibrium conditions. In crustal rocks most of the mass transport is related to mineral reactions. The proposed project quantitatively investigates processes occurring during mineral reactions in the carbonate system on a small scale. The new challenge of this proposal is the quantitative parameterization of non-equilibrium processes as its record of element and isotope zoning observed in natural samples contain information on the actual path, i.e. the operating mechanism and the time taken to get there. We hypothesize that the actual reaction mechanism depend on the deviation from the equilibrium state and that resulting zoning patterns can be resolved quantitatively. Hence, the proposed project aims to evaluate the dynamic evolution of mineral a composition in space and time along any P-T-X-t-path. Experiments will be carried out to systematically studying element and isotope exchange between co-existing mineral pairs. Experimental runs will be analyzed for surface processes and by compositional depth profiling. A numerical model will be developed to predict the reaction mechanism and the spatial composition of elements and isotopes during mineral reactions occurring along any given P-T-X-t-path. Modeling results will be tested against natural observations in regional carbonate bearing metamorphic rocks exhibiting reaction rims of ankerite surrounding cores of dolomite composition. The resulting knowledge provide the information on timescales necessary to equilibrate commonly used thermo(baro)meters which are inherently linked to all geochronology methods by the concept of diffusive closure. The gained knowledge can be used to extrapolate and estimate the rates of element and isotope transport through the crust and thus quantify their cycles in the Earth system.