Chemistry and Structure of Grain and Phase Boundaries: Importance for Trace Element Storage and Transport in the Mantle

这项工作旨在回答以下问题：“地幔岩石中不相容元素的晶界和相界的储存能力是多少？”以及“晶粒-晶粒界面的偏析如何影响地幔中的粒间扩散？”近年来发现，镁铁橄榄石晶粒间富含Ca、Al、Cr、K、Ti等元素。浓度随颗粒内部的浓度系统变化，在某些情况下遵循元素分配的经典热力学模型。本研究对这些过程及其对地幔扩散输运的影响进行了系统的分析和实验研究。这些结果将为地球深部的地球化学演化和行为提供约束。该提案的广泛影响体现在本科生的教育、研究生和博士后的专业发展以及新实验技术的建立。(1)地质与地球物理系是美国国家科学基金会资助的研究地球从表面到核心流体的REU站点。因此，本科生每年夏天都能获得实践经验，进行与本文件中提出的研究直接相关的实验。(2)本提案中概述的研究是一个项目的延续，该项目是最近博士奖学金项目的一部分，现在将由一名一年级研究生和一名年轻的博士后科学家进行，从而促进两者的专业发展。(3)发展新的实验技术，为建立固体地球科学的研究基础设施发挥重要作用。

This work seeks to answer the questions, "What is the storage capacity of grain and phase boundaries for incompatible elements in mantle rocks?" and "How does segregation to grain-grain interfaces affect intergranular diffusion in the mantle?" It was recently discovered that boundaries between grains of Mg-Fe olivine are enriched in elements such as Ca, Al, Cr, K and Ti. The concentrations vary systematically with the concentrations in the grain interiors, in some cases following classic thermodynamic models for elemental partitioning. This study involves systematic analytical and experimental investigation of these processes and the resultant effects on diffusive transport in Earth's mantle. The results will provide constraints on the geochemical evolution and behavior of Earth's deep interior. The broader impacts of this proposal emerge from education of undergraduates, professional development of a graduate student and a postdoctoral associate, and establishment of new experimental techniques. (1) The Department of Geology and Geophysics is an NSF-funded REU site for studies of Fluids in the Earth from Surface to Core. As such, undergraduates gain hands-on experience each summer carrying out experiments that are direct outgrowths of and intimately related to the research proposed in this document. (2) The research outlined in this proposal is a continuation of a project that was initiated as part of a recent doctoral fellowship project and will now be carried forward by a first-year graduate student and a young postdoctoral scientist, thus contributing to the professional development of both. (3) As part of the proposed research, new experimental techniques will be developed, which play an important part in building the research infrastructure in the solid-earth sciences.