Probing the Structure and Energetics of Reactive Sites at the Mineral-Water Interface: Implications for Element Partitioning and Geochronology

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9814691RakovanReactions that take place at the mineral-water interface (e.g., sorption and desorption, growth and dissolution, catalysis, etc.) affect many fundamental processes that occur on the Earth's surface. One of thehallmarks of mineral surface reactivity is its heterogeneous nature. Fundamental to understanding such heterogeneities is knowledge of the structure of protosites and the energetics of protosite reactions such assorption and incorporation. This project has two parallel goals. First, to determine the structure and energetics of different reactive surface sites that lead to heterogeneous reactivity of minerals; specifically heterogeneous adsorption and incorporation of trace metals into fluorite. This will be accomplished by using the differential incorporation REEs into fluorite as a probe of the structural differences between nonequivalent surface sites and to quantify energy differences associated with adsorption and incorporation of these elements. The resulting data will be the foundation for surface site selectivity models, which will be derived by first principle methods, based on molecular orbital theory. The second goal of this study will utilize the product of heterogeneous incorporation of REEs and the results from Part I to further develop a technique of intracrystalline isochron dating. In this method the Sm-Nd isotope systematics of coeval portions of compositionally different sectors of a single crystal are used to calculate an isochron age for the formation of that crystal, obviating several crucial assumptions required in normal isochron dating. This procedure thus represents a potentially powerful new method of dating that can complement more traditional techniques.