Modeling Deep Earth Fluids and Diamond Formation

模拟地球深层流体和钻石形成

• 批准号: 1624325
• 负责人: Dimitri Sverjensky
• 金额: $ 38万
• 依托单位: Johns Hopkins University
• 依托单位国家: 美国
• 项目类别: Continuing Grant
• 财政年份: 2016
• 资助国家: 美国
• 起止时间: 2016-11-01 至 2020-10-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1624325&HistoricalAwards=false
• 关键词: Modeling; Deep; Earth; Fluids; Diamond

The deep Earth is inaccessible for direct observation, but most people are well aware of its importance when earthquakes strike and volcanoes erupt. Less appreciated is the fact that the deep Earth has a role in regulating the Earth's atmosphere over the enormous span of geologic time. Fluids and volcanoes linking the deep Earth and the near-surface environment have played a major role in keeping our planet habitable over billions of years. For example, carbon dioxide in the atmosphere is cycled over time down into the Earth and back up through volcanic emissions via deep fluids and their chemical reactions with rocks. However, remarkably little is known about these fluids. Laboratory experimental studies seek to simulate them, geologists study rock samples for clues about them, and theoretical modeling is needed to synthesize a consistent picture of what is happening at depth. The current project seeks to advance such a synthesis. It is expected that advancing our understanding of fluids in the deep Earth will also help in building models for the evolution of and the search for life on other planets, particularly for the huge number of new planets being discovered outside our solar system. Previous models of fluids in the deep Earth have assumed they are Carbon-Oxygen-Hydrogen fluids containing molecular species (e.g. CO2, CH4, H2, and H2O) without aqueous ions. No quantitative models exist for the ionic speciation and reactivity of these fluids with their silicate environment at upper mantle conditions, which severely hampers understanding of planetary volatile evolution. The goal of this project is to develop a new approach to modeling the chemistry of deep fluids calibrated on experimental silicate and carbonate solubility measurements at high pressures, one that can be extrapolated to predict fluid-rock interactions under upper mantle conditions. It is proposed to develop predictive theoretical models for investigating the nature and reactivity of deep fluids in the Earth with specific application to the deep carbon cycle. A key issue to be investigated is the nature of the species in deep fluids. In particular, metal-silicate and carbonate complexes will be studied by modeling published experimental solubilities of important upper mantle mineral assemblages and new experimental solubilities of aragonite at elevated temperatures and pressures. The model will then be tested with published fluid inclusion compositions in diamonds and coexisting mineral compositions to develop aqueous speciation models for the end-member fluids thought to form diamonds. Building on these results, chemical mass transfer models will be developed to enable a quantitative understanding of the chemical processes involved in the formation of diamonds from metasomatic fluids in the peridotitic environment of the subcratonic lithospheric mantle.

地球深处无法直接观测，但大多数人都很清楚地震和火山爆发时它的重要性。很少有人认识到的是，在漫长的地质时期内，地球深部在调节地球大气层方面发挥着作用。连接地球深层和近地表环境的流体和火山在数十亿年来保持我们的星球可居住方面发挥了重要作用。例如，大气中的二氧化碳随着时间的推移循环进入地球，并通过火山排放物通过深层流体及其与岩石的化学反应返回地球。然而，人们对这些流体知之甚少。实验室实验研究试图模拟它们，地质学家研究岩石样本以获得有关它们的线索，需要理论建模来合成关于深度发生的一致图片。目前的项目力求推动这种综合。预计，提高我们对地球深处流体的了解也将有助于建立其他行星进化和寻找生命的模型，特别是对于太阳系外正在发现的大量新行星。以前的地球深部流体模型假设它们是碳-氧-氢流体，含有分子物质（例如CO2，CH 4，H2和H2O），没有水离子。没有定量模型存在的离子形态和反应性的这些流体与他们的硅酸盐环境在上地幔条件下，这严重阻碍了行星挥发性演化的理解。该项目的目标是开发一种新的方法来模拟在高压下实验硅酸盐和碳酸盐溶解度测量校准的深部流体化学，可以外推预测上地幔条件下的流体-岩石相互作用。建议开发预测性理论模型，用于调查地球深部流体的性质和反应性，并具体应用于深部碳循环。需要研究的一个关键问题是深层流体中物种的性质。特别是，金属硅酸盐和碳酸盐复合物将通过模拟重要的上地幔矿物组合和新的实验溶解度的文石在高温高压下公布的实验溶解度进行研究。然后，该模型将进行测试与公布的流体包裹体成分的钻石和共存的矿物成分，以开发水的端员流体被认为是形成钻石的形态模型。建立在这些结果的基础上，化学传质模型将开发，使参与形成金刚石的交代流体中的橄榄岩环境中的亚地幔岩石圈地幔的化学过程的定量了解。