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

地球深处的流体：高压和高温下的拉曼光谱

• 批准号: NE/H011242/1
• 负责人: Michael Walter
• 金额: $ 3.74万
• 依托单位: University of Bristol
• 依托单位国家: 英国
• 项目类别: Research Grant
• 财政年份: 2010
• 资助国家: 英国
• 起止时间: 2010 至 无数据
• 项目状态: 已结题
• 来源: https://gtr.ukri.org/projects?ref=NE%2FH011242%2F1
• 关键词: Fluids; Deep; Earth; Raman; Spectroscopy

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.

流体在地球内部深处的地球化学中起着巨大的作用，尽管它们相对于固体岩石地幔的丰度相对较低。这些流体主要由挥发性组分碳、氧、氢和硫（COHS）组成。它们在岩浆生成中很重要，因为即使是少量的流体也可以彻底改变岩石的熔融行为。它们在物质传递中也很重要，因为它们在一个叫做交代作用的过程中改变了所经过的岩石。正是从这样的流体中，钻石沉淀在地幔深处。也许它们最大的影响是它们可以调节地幔的氧化态，或者所谓的氧逸度。尽管它们对地幔地球化学非常重要，但对于哪些化合物或物种在地幔温度和压力下实际上是稳定的，实验上知之甚少。目前，我们必须依赖于热力学计算，这些计算基于非常少的实验数据。然而，构成地幔流体的COHS化合物的物种形成的知识是理解许多地幔过程的基础。这种信息的缺乏来自于一旦保持在高压和高温下的典型样品被冷却并减压到环境条件时，在冻结或“淬火”流体物质方面的固有困难-几乎所有的信息都在淬火过程中丢失。这就需要一种技术，使人们能够探测流体样品，而他们在高压和高温。显微拉曼光谱是一种已被成功用于识别，并在某些情况下，量化，在矿物中捕获的流体包裹体中的物种的技术，这种强大的原位技术开始被应用于流体在高P和T的金刚石砧室。本提案的目的是在我们的实验室中开发所需的技术，用于在高压（例如1 - 50 GPa）和高温（例如1000 - 2000 K）下以及在固定的氧逸度下保持的COHS流体的原位拉曼光谱测量。实验是在金刚石压砧单元（DAC）中进行的，由于金刚石的透明度，DAC允许在高P和T下对流体样品进行光谱测量。在本提案中，我们申请种子资金用于一个为期两年的计划，以修改我们目前的实验能力，以便在DAC中进行高P-T显微拉曼实验，开发和改进样品制造技术，并进行概念验证和校准实验。该项目将为我们实验室的一项新的令人兴奋的实验举措铺平道路。