CSEDI Collaborative Research: Valence state of iron in the lower mantle

CSEDI合作研究：下地幔铁的价态

• 批准号: 1316022
• 负责人: Sang-Heon Shim
• 金额: $ 6.94万
• 依托单位: Arizona State University
• 依托单位国家: 美国
• 项目类别: Continuing Grant
• 财政年份: 2012
• 资助国家: 美国
• 起止时间: 2012-10-01 至 2015-08-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1316022&HistoricalAwards=false
• 关键词: CSEDI; Collaborative; Research; Valence; state

The redox state controls many important chemical reactions in natural systems, including the reactions in the deep interior of the Earth. The oxidation state of iron has been extensively used to infer the redox state. It has been well understood that the upper mantle has reducing redox conditions and thermodynamic studies have predicted even more reducing conditions in the lower mantle. However, recent studies at pressure-temperature conditions related to the topmost lower mantle have shown that about 60% of iron in the dominant lower-mantle mineral, magnesium silicate perovskite, is ferric. This is very surprising because only 2% of iron is ferric in upper-mantle minerals. If this result is extrapolated to the deep lower mantle, it would imply that the lower mantle is chemically distinct from the upper mantle, which may conflict with recent seismic tomography evidence of mixing between the upper and lower mantle. Our preliminary work showed that the oxidation state of iron in mantle silicate perovskite is strongly coupled with the electronic configuration of iron at high pressure. As recent studies have shown that the electronic configuration of iron in mantle minerals changes with depth, our preliminary work implies that the oxidation state of iron may change with depth as well. In addition, aluminum in silicate perovskite can influence the oxidation state of iron. In this project, we will combine experiment (Shim) and theory (Morgan) to measure how the oxidation state of iron in lower-mantle silicate perovskite changes with depth and composition. In the experimental effort, we will measure the oxidation state of iron by controlling the redox state of the sample chamber to that of the lower mantle at high pressure-temperature. We use ab-initio based techniques, which solve the fundamental quantum mechanical equations for the material, to predict reaction energies and volumes as a function of composition, pressure, and temperature. This joint effort will provide graduate students and postdocs with new opportunities to combine experimental and theoretical approaches.

氧化还原国家控制着自然系统中许多重要的化学反应，包括地球深内部的反应。 铁的氧化态已被广泛用于推断氧化还原状态。 众所周知，上地幔具有降低的氧化还原条件，并且热力学研究预测了下地幔中的更还原条件。 然而，最近对与最高地幔有关的压力温度条件的研究表明，在主要的下层矿物矿物质硅酸镁钙钛矿中约有60％的铁是铁的。 这是非常令人惊讶的，因为只有2％的铁在上层矿物质中是铁。 如果将此结果推送到深层地幔，则意味着下层在化学上与上地幔不同，这可能与最近的地震层析成像证据相抵触，表明上地幔之间混合了上地幔。 我们的初步工作表明，地幔硅酸盐钙钛矿中铁的氧化状态与铁在高压下的电子构型强烈结合。 正如最近的研究表明，地幔矿物质中铁的电子构型随深度的变化而变化，我们的初步工作意味着铁的氧化状态也可能随深度变化。 另外，硅酸盐钙钛矿中的铝会影响铁的氧化态。 在这个项目中，我们将结合实验（SHIM）和理论（Morgan），以测量在下层硅酸盐钙钛矿中铁的氧化状态如何随深度和组成而变化。 在实验性的工作中，我们将通过控制样品室的氧化还原状态到高压温度下的下地幔的氧化剂状态。我们使用基于Ab-Initio的技术，该技术可以解决材料的基本量子机械方程，以预测反应能和体积，这是组成，压力和温度的函数。 这项共同的努力将为研究生和博士后提供新的机会，以结合实验和理论方法。