Solid State Geochemistry: High Resolution Transmission Electron Microscopy of Minerals

该项目的目标是研究对地质和环境有重要意义的矿物的化学和结构偏离理想状态的情况。这样的偏差可以掌握地质过程和地质过去的重要线索。电子衍射、电子能谱、高分辨率电子显微镜成像、图像的计算机模拟和结构模型的计算将结合起来解决微晶和纳米晶矿物的问题。蛇纹石矿物是洋盆下超镁铁质岩石的重要成分。它们很可能是俯冲过程中水进入地幔的重要载体；水的释放促进了上覆地幔楔体的部分熔融和岩浆作用，从而导致火山活动。俯冲的蛇纹岩也影响着深部地震的发展。鉴于它们在构造上的重要性，获得尽可能多的关于它们的基本知识是很重要的。这项拟议的研究将解决关于反辉石和温石棉蛇纹石的构造问题，具有潜在的地球物理影响。石榴石具有名义上的立方对称性，但许多石榴石表现出非立方性质。初步的HRTEM和X射线衍射测量表明，阳离子有序性是导致它们的对称性低于立方对称性的原因。这些数据将被提炼，如果得到证实，将被用来产生一个化学有序模型，以解释它们的异常特征。许多对环境具有重要意义的矿物形成于地球表面或其附近。了解结晶不良材料的结构状态对于了解风化、重金属沉积和土壤形成很重要。这些低温组合通常出现在细粒矿物的亲密、非均质混合物中。使用电子纳米衍射(完)，可以研究几个纳米立方米的体积--比任何其他衍射方法小许多个数量级。END将用于研究水合氧化铁矿物，统称为亚铁水合物及其生物近亲铁蛋白，以及在电子显微镜下遭受快速辐射损害的材料，如粘土。

BuseckEAR-0003533The goal of this project is to examine chemical and structural deviations from ideality in geologically and environmentally significant minerals. Such deviations can hold important clues to geological processes and to the geological past. Electron diffraction, electron spectroscopy, high-resolution TEM imaging, computer simulation of images, and calculation of structure models will be combined to solve problems of micro- and nanocrystalline minerals. The serpentine minerals are important constituents of ultramafic rocks underlying the oceanic basins. They are likely significant carriers of water into the mantle during subduction; the release of that water promotes partial melting and magmatism in the overlying mantle wedge, leading to volcanism. Subducted serpentines also influence the development of earthquakes at depth. Given their tectonic importance, it is important to obtain as much fundamental knowledge as possible about them. The proposed research will resolve structural problems regarding antigorite and chrysotile serpentine, with potential geophysical implications. Garnets have nominally cubic symmetry, but many display non-cubic properties. Preliminary HRTEM and XRD measurements suggest cation ordering as the source of their lower than cubic symmetry. These data will be refined and, if confirmed, be used to produce a model of chemical ordering to explain their anomalous characteristics. Many minerals that are of great environmental importance form at or near Earth's surface. Knowledge of the structural states of poorly crystallized materials is important for understanding weathering, heavy-metal deposition, and soil formation. These low-temperature assemblages typically occur in intimate, heterogeneous mixtures of fine-grained minerals. Using electron nanodiffraction (END), it is possible to study volumes of a few nm3 - many orders of magnitude less than by any other diffraction method. END will be used to investigate the hydrous ferric oxide minerals that are collectively called ferrihydrite and their biological cousin ferritin and materials such as clays that suffer rapid radiation damage during electron microscopy.