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

发生在矿泉水界面的拉科万反应(如吸附和解吸、生长和溶解、催化等)影响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。理解这种异质性的基础是了解原生生物的结构和原生生物反应的能量学，如分类和结合。这个项目有两个平行的目标。首先，确定导致矿物异质反应性的不同活性表面位置的结构和能量；特别是痕量金属在萤石中的异质吸附和掺入。这将通过使用稀土在萤石中的差示掺入作为不同表面位置之间的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。得到的数据将是表面位选择性模型的基础，该模型将基于分子轨道理论，通过第一性原理方法得到。这项研究的第二个目标是利用稀土非均相掺入的产物和第一部分的结果来进一步发展晶体内等时线测年技术。在这种方法中，利用单晶不同成分扇区的共生部分的Sm-ND同位素系统学来计算该晶体形成的等时线年龄，从而省去了正常等时线测年所需的几个关键假设。因此，这一程序代表了一种潜在的强大的新测年方法，可以补充更传统的技术。

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.