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Microchemistry and microstructure of Australian Opal

澳大利亚蛋白石的微观化学和微观结构

基本信息

批准号：
268285275
负责人：
Privatdozent Dr. Ralf Milke
金额：
--
依托单位：
Institut für Geologische Wissenschaften
依托单位国家：
德国
项目类别：
Research Grants
财政年份：
2014
资助国家：
德国
起止时间：
2013-12-31 至 2018-12-31
项目状态：
已结题

来源：
https://gepris.dfg.de/gepris/projekt/268285275?language=en
关键词：
Microchemistry microstructure Australian Opal

项目摘要

Precipitation of colloidal amorphous silica (opal-A) occurs in various geologically important settings on earth´s surface and subsurface. Common opal is composed of disordered heterogeneous spheres. In contrast, precious opal composed of uniform spheres packed in highly regular arrays, occurs in very few scattered deposits. At present, there is no satisfactory explanation of the opal formation mechanisms available due to the complex nature of opal-forming fluids in geological systems. Detailed investigations of opals and their host rocks are urgently needed to establish a mineralogic understanding of chemical re-distribution scales and mechanisms during silicate rock alteration and silica diagenesis.In this proposal we ask for support of analytical investigations that aim at the mechanisms of nanocolloidal sphere formation in natural Australian opal-A. This study will focus on the key processes in opal genesis - the formation of spheres with an individual size distribution and their three-dimensional arrangement. We will use a novel approach, combining opal microstructure and microchemistry, to confine the geochemistry of the silica colloid system, and to close the gap between available analytical methods at high spatial resolution and current knowledge.The geochemical fingerprint of opals formed during sedimentation or pseudomorphism will give insights into systematic element exchange at essentially different conditions. The detailed investigation of chemical and mineralogical properties of host rocks and cogenetic minerals will provide clues about pH and salinity of the opal-forming solutions. Microstructural analysis will reveal how the type and quantity of impurities modify the short-range order of natural amorphous silica. Additionally, detailed study of opal pseudomorphs´ texture and composition will reveal clues for structural and chemical reorganization mechanisms behind silica pseudomorphism.The micromorphology and chemistry of opals and cogenetic phases will be determined with scanning electron microscopy (SEM) and electron microprobe analysis (EMPA). The precise structural characterization of opals will be accomplished with micro-X-ray diffraction (micro-XRD) and micro-Raman spectroscopy (micro-RS). Concentration profiles at replacement interfaces in pseudomorphs will be studied with a NanoSIMS ion microprobe and high spatial resolution transmission electron microscopy (TEM) techniques, such as HRTEM, EFTEM-EELS, and TEM-EDX.Research on opal geochemistry is so far largely restricted to bulk analysis of opal samples by mass spectroscopic methods. Any systematic relation between chemical composition and silica sphere size, size distribution, and package ordering is ignored by these approaches, as well as chemical contamination by mineral inclusions, on the one hand, and information on solution composition to be gained from included and cogenetic minerals on the other. We ask for support to bring the resea

胶体无定形二氧化硅（蛋白石-A）的沉淀发生在地球表面和地下的各种地质重要环境中。普通蛋白石是由无序的非均匀球体组成。相比之下，珍贵的蛋白石组成的均匀球体包装在高度规则的阵列，出现在非常少的分散存款。由于地质系统中蛋白石形成流体的复杂性，目前对蛋白石形成机制还没有令人满意的解释。蛋白石和他们的寄主岩石的详细调查，迫切需要建立一个矿物学的理解，在硅酸盐岩石蚀变和二氧化硅成岩作用过程中的化学再分布规模和机制，在这个建议中，我们要求支持的分析调查，目的是在天然澳大利亚蛋白石-A的纳米胶体球形成的机制。这项研究将集中在蛋白石成因的关键过程-形成的球体与个人的大小分布和他们的三维排列。我们将使用一种新的方法，结合蛋白石微观结构和微观化学，限制硅胶体系统的地球化学，并关闭差距之间的分析方法在高空间分辨率和现有的knows.The地球化学指纹蛋白石沉积或假像形成过程中将提供洞察系统的元素交换在本质上不同的条件。对寄主岩石和同生矿物的化学和矿物学性质的详细研究将提供有关蛋白石形成溶液的pH值和盐度的线索。微观结构分析将揭示杂质的类型和数量如何改变天然无定形二氧化硅的短程有序。此外，对蛋白石假晶的结构和成分的详细研究将揭示硅假晶背后的结构和化学重组机制的线索。蛋白石和共生相的微观形态和化学将通过扫描电子显微镜（SEM）和电子探针分析（EMPA）来确定。蛋白石的精确结构表征将通过显微X射线衍射（micro-XRD）和显微拉曼光谱（micro-RS）来完成。利用NanoSIMS离子探针和高空间分辨率透射电子显微镜（TEM）技术，如HRTEM、EFTEM-EELS和TEM-EDX，研究假晶体中置换界面的浓度分布。这些方法忽略了化学成分和二氧化硅球的大小，大小分布和包排序之间的任何系统关系，以及矿物包裹体的化学污染，一方面，和溶液组成的信息，以获得从包括和同生矿物。我们请求支持，