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

发生在矿物-水界面的反应（如吸附和解吸、生长和溶解、催化等）影响着发生在地球表面的许多基本过程。矿物表面反应性的标志之一是它的非均质性。理解这种非均质性的基础是了解原生质结构和原生质反应的能量学，如分类和合并。这个项目有两个平行的目标。首先，确定导致矿物非均相反应性的不同反应表面位点的结构和能量学；特别是异质吸附和结合微量金属到萤石。这将通过使用稀土元素在萤石中的差异掺入量作为非等效表面位点之间结构差异的探针来实现，并量化与这些元素的吸附和掺入相关的能量差异。所得数据将成为基于分子轨道理论的第一性原理方法推导表面位点选择性模型的基础。本研究的第二个目标是利用稀土非均相结合的产物和第一部分的结果进一步发展晶内等时线定年技术。在这种方法中，使用单晶组成不同部分的同计算部分的Sm-Nd同位素系统来计算该晶体形成的等时线年龄，从而消除了正常等时线定年所需的几个关键假设。因此，这一过程代表了一种潜在的强大的新的测年方法，可以补充更多的传统技术。

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.