Solid State Geochemistry: High Resolution Transmission Electron Microscopy of Minerals

该项目的目标是检查具有重要地质和环境意义的矿物的化学和结构偏离理想状态。这种偏差可以为地质过程和地质历史提供重要线索。结合电子衍射、电子能谱、高分辨率TEM成像、图像计算机模拟、结构模型计算等方法，解决微、纳米晶体矿物问题。蛇纹岩矿物是大洋盆地下伏超镁铁质岩的重要组成部分。在俯冲过程中，它们可能是水进入地幔的重要载体；这些水的释放促进了上覆地幔楔的部分熔融和岩浆活动，导致火山活动。俯冲的蛇纹岩也影响地震在深部的发展。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础知识是很重要的。建议的研究将解决反长花岗岩和温石棉蛇纹石的结构问题，具有潜在的地球物理意义。石榴石名义上具有立方对称性，但许多石榴石显示出非立方性质。初步的HRTEM和XRD测量表明阳离子有序是其低于立方对称性的来源。这些数据将被改进，如果得到证实，将被用来产生一个化学排序模型来解释它们的异常特征。许多对环境有重要意义的矿物都是在地表或地表附近形成的。了解低结晶材料的结构状态对于理解风化、重金属沉积和土壤形成非常重要。这些低温组合通常发生在细粒矿物的紧密非均质混合物中。使用电子纳米衍射（END），可以研究几nm3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（统称为水合氧化铁）及其生物表亲铁蛋白，以及在电子显微镜下遭受快速辐射损伤的粘土等材料。

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.