Microstructural Investigation of Evaporitic Silica

本申请申请的资金将用于支持普林斯顿大学Peter J. Heaney教授及其研究小组对微晶二氧化硅SiO2的研究。这项工作将探索二氧化硅微观结构如何反映它们形成的环境的化学性质。尽管这些类型的研究已被广泛用于海洋生物二氧化硅，但蒸发环境中二氧化硅矿物的结构特征仍然相对未知。我们对这些阶段的无知尤其不幸，因为蒸发硅石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和同事将确定蒸发二氧化硅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)新发现的二氧化硅多晶莫干石的微观结构分析；2)确定含水硅酸钠镁硬岩晶体结构及镁硬岩与莫干石的结构通道；3)蒸发二氧化硅与先前存在的碳酸盐之间的替代机制的研究。这项工作将建立对蒸发沉积中二氧化硅矿物成岩蚀变的微观结构认识，并将在原子尺度上揭示壳碳酸盐的硅化机制，并为化石过程提供线索。

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.