Modeling Deep Earth Fluids and Diamond Formation

地球深处无法直接观测，但当地震来袭和火山喷发时，大多数人都很清楚它的重要性。较少被认识到的事实是，地球深处在巨大的地质时间跨度中扮演着调节地球大气层的角色。流体和火山将地球深处和近地表环境联系在一起，在数十亿年来保持地球宜居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，并通过深部流体的火山排放及其与岩石的化学反应返回地球。然而，令人惊讶的是，人们对这些液体知之甚少。实验室实验研究试图模拟它们，地质学家研究岩石样本以寻找关于它们的线索，需要理论建模来合成关于深度发生的一致的图景。目前的项目旨在推进这样的综合。预计推进我们对地球深处流体的了解也将有助于建立其他行星上生命演化和寻找的模型，特别是在我们的太阳系之外发现的大量新行星。以前的地球深部流体模型假设它们是碳-氧-氢流体，含有分子物种(如CO2、CH4、H2和H2O)，不含水离子。在上地幔条件下，这些流体的离子形态和与其硅酸盐环境的反应性没有定量的模型，这严重阻碍了对行星挥发分演化的理解。该项目的目标是开发一种新的方法来模拟深部流体的化学，该方法根据高压下实验的硅酸盐和碳酸盐溶解度测量进行校准，可以外推以预测上地幔条件下的流体-岩石相互作用。建议开发用于研究地球深层流体的性质和反应性的预测性理论模型，并将其具体应用于深层碳循环。需要研究的一个关键问题是深部流体中物种的性质。特别是，将通过模拟已发表的重要上地幔矿物组合的实验溶解度和文石在高温和压力下的新实验溶解度来研究金属硅酸盐和碳酸盐络合物。然后，将用已公布的钻石中的流体包裹体成分和共存的矿物成分对该模型进行测试，以开发被认为形成钻石的终端成员流体的水形态模型。在这些结果的基础上，将开发化学传质模型，以便能够定量了解在克拉通以下岩石圈地幔的橄榄岩环境中交代流体形成钻石所涉及的化学过程。

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.