Microstructural Investigation of Evaporitic Silica

Heaney 9418031这项提案所要求的资金将支持普林斯顿大学的Peter J.Heaney教授和他的研究小组对微晶二氧化硅的研究。这项工作将探索二氧化硅微结构反映其形成环境的化学成分的方式。尽管人们对生物成因的海相二氧化硅进行了大量的研究，但蒸散环境中的二氧化硅矿物的结构特征仍然相对未知。我们对这些阶段的忽视尤其令人遗憾，因为蒸散性二氧化硅是一个重要的古气候指标，通常与经济矿石有关。通过使用透射电子显微镜、粉末X射线衍射和电子探针显微分析，Heaney和他的同事将确定蒸散状二氧化硅的形成和随时间变化的方式。这些研究将涉及三个相互关联的项目：1)莫干石的显微结构分析，这是一种新发现的二氧化硅多晶型；2)水合硅酸盐镁闪石的晶体结构测定以及镁闪石与莫甘石之间的结构路径；3)蒸发二氧化硅与先前存在的碳酸盐之间的置换机制的检验。这项工作将建立对蒸散质矿床中二氧化硅矿物成岩蚀变的微观结构的认识，并将在原子尺度上揭示贝壳碳酸盐的硅化机理，并将有助于揭示石化过程。

Heaney 9418031 The funds requested in this proposal will support Professor Peter J. Heaney of Princeton University and his research group in their investigations of microcrystalline silica SiO2 . This work will explore the ways in which silica microstructures reflect the chemistry of the environments in which they formed. Although these kinds of investigations have been intensively pursued for biogenic marine silica, the structural characteristics of silica minerals from evaporitic environments remain relatively unknown. Our ignorance of these phases is especially unfortunate, since evaporitic silica is an important paleoclimatic indicator and is commonly associated with economic ores. By using transmission electron microscopy, powder X-ray diffraction, and electron probe microanalysis, Heaney and coworkers will determine the way in which evaporitic silica forms and transforms over time. These studies will involve three interrelated projects: 1) Microstructural analysis of moganite, a newly recognized silica polymorph; 2) Determination of the crystal structure of the hydrous sodium silicate magadiite and the structural pathway between magadiite and moganite; and 3) Examination of replacement mechanisms between evaporitic silica and preexisting carbonate. This work will establish a microstructural understanding of the diagenetic alteration of silica minerals from evaporitic deposits, and it will reveal silicification mechanisms of shell carbonate at the atomic scale and should shed light on fossilization processes.