Fluids in the Deep Earth: Raman Spectroscopy at High Pressures and Temperatures

流体在地球深处的地球化学中扮演着重要的角色，尽管相对于固体的岩石地幔，它们的丰度相对较低。这些流体主要由挥发性组分碳、氧、氢和硫（COHS）组成。它们在岩浆的形成中很重要，因为即使是少量的流体也能极大地改变岩石的熔化行为。它们在质量传递中也很重要，因为它们在一个叫做交代作用的过程中改变了穿过的岩石。钻石就是从这些流体中沉淀到地幔深处的。也许它们最大的影响在于它们可以调节地幔的氧化态，即所谓的氧逸度。尽管它们对地幔地球化学很重要，但在实验上，我们对哪些化合物或物种在地幔温度和压力下是稳定的知之甚少。目前我们必须依靠基于很少实验数据的热力学计算。然而，了解构成地幔流体的COHS化合物的种类是理解许多地幔过程的基础。这种信息的缺乏来自固有的冻结或“淬火”的困难，一旦一个典型的样品在高压和高温下被冷却和减压到环境条件下，几乎所有的信息都在淬火过程中丢失了。这就需要一种能够在高压和高温下探测流体样本的技术。微拉曼光谱是一种非常成功的技术，用于识别，在某些情况下，用于量化被困在矿物中的流体包裹体中的物种，这种强大的原位技术开始应用于钻石砧细胞中高P和高T的流体。本提案的目的是开发我们实验室所需的技术，用于在高压（例如1 - 50 GPa）和高温（例如1000 - 2000 K）和固定氧逸度下对COHS流体进行原位拉曼光谱测量。实验是在钻石砧池（DAC）中进行的，由于钻石的透明度，允许光学进入流体样品进行高P和t的光谱测量。在本提案中，我们要求为一个为期两年的计划提供种子资金，以修改我们目前的实验能力，以便在DAC中进行高P- t微拉曼实验，开发和完善样品制造技术，并进行概念验证和校准实验。这个项目将为我们实验室进行一项令人兴奋的新实验铺平道路。

Fluids play a huge role in the geochemistry of the Earth's deep interior, even though they are present at relatively low abundance relative to the solid, rocky mantle. These fluids are comprised primarily of the volatile components carbon, oxygen, hydrogen and sulfur (COHS). They are important in magma generation as even a small amount of fluid can drastically alter the melting behavior of a rock. They are also important in mass transfer by altering the rocks they pass through in a process called metasomatism. It is from such fluids that diamonds precipitate in the deep mantle. Perhaps their greatest influence is in the way they can mediate the oxidation state, or the so-called oxygen fugacity, of the mantle. For all their importance to mantle geochemistry, very little is known experimentally about what compounds, or species, are actually stable at mantle temperatures and pressures. Currently we must rely on thermodynamic calculations that are based on very little experimental data. Yet knowledge of the speciation of the COHS compounds that comprise mantle fluids is fundamental for understanding many mantle processes. This lack of information comes from an inherent difficulty in freezing in, or 'quenching', the fluid species once a typical sample held at high pressure and temperature is cooled and decompressed to ambient conditions - nearly all the information is lost during the quenching process. This necessitates a technique that allows one to probe fluid samples while they are at high pressures and temperatures. Micro-Raman spectroscopy is a technique that has been used with great success to identify, and in some cases to quantify, the species in fluid inclusions trapped in minerals, and this powerful in situ technique is beginning to be applied to fluids at high P and T in the diamond anvil cell. The purpose of this proposal is to develop the techniques in our lab required for in situ Raman spectroscopic measurements of COHS fluids held at high pressures (e.g. 1 - 50 GPa) and high temperatures (e.g. 1000 - 2000 K), and at a fixed oxygen fugacity. Experiments are done in a diamond anvil cell (DAC) which, because of the transparency of the diamonds, allows optical access to the fluid sample for spectroscopic measurements at high P and T. In this proposal we are requesting seed funding for a two-year program to modify our current experimental capabilities in order to carry out high P-T micro-Raman experiments in the DAC, develop and refine sample fabrication techniques, and carry out proof-of-concept and calibration experiments. This project will pave the way for a new and exciting experimental initiative in our laboratory.