TEM Studies of Weathering Reactions: The Importance of Mineral Structure, Microstructure and Composition

化学风化非常重要，因为它是在高温高压下形成的硅酸盐矿物转化为沉积物和土壤成分的过程。尽管如此，对许多反应的机制和转化速率的结构和组成控制仍然知之甚少。本提案描述了两个研究项目，旨在使用高分辨率透射电子显微镜研究风化反应的微观特征，其中母体和产物矿物之间存在显着结构。其中第一个涉及角闪石群矿物的水化和氧化。第二个项目侧重于钙钛矿风化，其中不形成含水矿物，也不会发生氧化。本文研究了具有接近端元成分的微结构复杂角闪石、互生和外露角闪石以及含有链宽缺陷的角闪石的风化反应。交错生长的角闪石提供了在相同的物理化学条件下比较风化速率和机制的机会，并评估了反应的程度，这些反应是由相干应变、缺陷和晶界集中的。并对钙钛矿的风化进行了研究。作为核废料贮存陶瓷的一种可能成分，钙钛矿的水热溶解已被广泛研究，但其自然风化反应在很大程度上被忽视。化学上简单的转化为TiO2矿物可能涉及相当大的结构遗传。这些项目的目的是澄清自然风化过程的晶体化学细节，从而增强我们对这些反应发生的机制的理解。

Chemical weathering is of fundamental importance because it is the process by which silicate minerals formed at high-temperatures and pressures are converted to the constituents of sediments and soils. Despite this, the structural and compositional controls on the mechanisms and rates of transformations of many reactions are still poorly understood. This proposal describes two research projects designed to use high-resolution transmission electron microscopy to investigate the microscopic characteristics of weathering reactions where significant structural exists between the parent and product minerals. The first of these involves hydration and oxidation of amphibole-group minerals. The second project focuses on perovskite weathering, where hydrous minerals are not formed and oxidation does not occur. The weathering reactions of a selection of microstructurally complex amphiboles with close to end-member compositions, intergrown and exsolved amphiboles, and amphiboles containing chain-width defects will be examined. Intergrown amphiboles offer the opportunity to compare weathering rates and mechanisms under the same physiochemical conditions and to evaluate the degree to which reactions are focused by coherency strain, defects, and grain boundaries. The Weathering of perovskite will also be examined. Hydrothermal dissolution of perovskite, a possible component of nuclear waste storage ceramics, has been studied extensively, but the natural weathering reactions have been largely ignored. The chemically simple transformation to TiO2 minerals may involve considerable structural inheritance. The aims these projects are to clarify the crystal chemical details of the natural weathering processes, thus enhancing our understanding of the mechanisms by which these reactions occur.