A mineral-physics based model of mantle electrical conductivity

基于矿物物理学的地幔电导率模型

• 批准号: 1112861
• 负责人: Steven Constable
• 金额: $ 35.72万
• 依托单位: University of California-San Diego Scripps Inst of Oceanography
• 依托单位国家: 美国
• 项目类别: Continuing Grant
• 财政年份: 2011
• 资助国家: 美国
• 起止时间: 2011-06-01 至 2016-05-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1112861&HistoricalAwards=false
• 关键词: mineral; physics; based; model; mantle

Many of the tectonic processes expressed at Earth's surface are themanifestation of processes rooted deeper within the planet. Variations intemperatures and composition of the upper mantle (the layer below thecrust) combined with the forces that drive motion contribute to thedeformation patterns at the surface and/or melt generation (possiblyresulting in volcanoes). Models of the mantle further our understandingof the evolution of these processes, but these models require accurateestimates of temperature and composition of the upper mantle---neitherof which can be measured directly. To estimate the state of the mantle,geophysical models of a physical property sensitive to temperature andcomposition are typically used as a proxy (e.g. seismic velocity and electricalconductivity). Using electrical conductivity as a proxy requireslaboratory measurements on minerals at a range of conditions expectedfor the mantle. Most interpretations of upper mantleelectrical conductivity are based only on the mineral olivine,which comprises 60-70% of the mantle, and often ignore the possibleinfluence of the remaining mineral components. While olivine typicallydominates the electrical conductivity, there are cases, particularlywhen bound water content is high, where electrical conductivitycontributions from orthopyroxene and clinopyroxene, the next mostabundant upper mantle minerals, may be disproportionate to their volume.This project will involve the collection of electrical conductivity onmantle pyroxenes in a laboratory controlled setting over a wide range ofphysical conditions, leading to an improved model of dry pyroxeneconductivity. This model will help improve current,and aid in future, interpretations of mantle conductivity models and theprocesses that potentially drive melt generation and surface dynamics.This project will also include the building of a conductivity apparatusthan can be used in future studies as well as the training of a postdoc.There have been few electrical conductivity studies on orthopyroxene andfewer on clinopyroxene. While they suggest anhydrous conductivity oforthopyroxene is similar to that of olivine, with clinopyroxene about oneorder of magnitude lower, they were conducted along predetermined oxygenfugacity paths, thus limiting their application to specific conditions. This projectwill focus on the collection of electrical conductivity and thermopowermeasurements on mantle derived pyroxenes over a wide range oftemperatures and oxygen fugacities relevant to the mantle. Bycollecting thermopower measurements in tandem with electricalconductivity at several oxygen fugacity states and temperatures itwill be possible to estimate the concentration and mobility of thevarious charge carriers and build point defect models that extendconductivity estimates to a much larger range of mantle conditions. Asimilar model for olivine has become a standard for comparison withlaboratory experiments and repeatedly verified in recent experiments.In the past few years there has been a great deal of attention paid tothe effect of water on olivine conductivity. However, water partitioningexperiments show that pyroxenes may hold ten times as much bound H2O asolivine. Apart from contributing to bulk composition, pyroxenites (rockswith 50% pyroxene) are found regionally in veins which are important tothe geochemical budget, and may be responsible for the "garnetsignature" in mid-ocean ridges and ocean island basalts. If such veinsform interconnected networks they would have a disproportionate effecton mantle conductivity. A reliable anhydrous pyroxene conductivitymodel developed as part of this study will aid interpretation of futureelectrical conductivity experiments on hydrous pyroxenes, as well as improve the interpretation of mantle conductivities inferred fromelectromagnetic sounding.

在地球表面表达的许多构造过程都是植根于行星内深处的过程的侵占。 上地幔的变化构成和组成（下方的层）结合了驱动运动的力，有助于表面和/或熔体产生（可能在火山中呈现）。 地幔的模型进一步了解了这些过程的演变，但是这些模型需要准确地估计上地幔的温度和组成 - 既不能直接测量。 为了估计地幔的状态，通常将对温度和重点敏感的物理特性的地球物理模型用作代理（例如地震速度和电导率）。 使用电导率作为代理需要在预期地幔预期的一系列条件下对矿物进行详细测量。 上地幔电导率的大多数解释仅基于矿物橄榄石，该矿物橄榄石占地幔的60-70％，并且通常忽略其余矿物质成分的可能性。 虽然橄榄石通常会降低电导率，但在某些情况下，尤其是绑定的水分含量很高，而从正pypyroxene和Clinopyroxene产生的电导率构造是下一个最重要的上地幔矿物质，这可能与它们的体积不成比例。这些项目将涉及对电导率的收集，从而使电导率遍及一定范围，该范围是在层次上构成的，该阶段是在层次上，构造了一个范围的范围，该阶段是构造的，构成了层次的范围。改善了干pyroxeneconconductivity的模型。 该模型将有助于改善当前的电导率模型和可能推动融化产生和表面动力学的过程的解释。该项目还将包括在未来的研究中使用电导率Aptaratusthan，以及对多核后的培训。几乎没有对Orthopyroxene和Feweroxene on Clinepoyroderroxene上的电导率研究。 虽然它们认为非拷贝性无水电导率与橄榄石相似，而斜二烯二级级较低，但它们沿预先确定的氧气路径进行，从而限制了它们在特定条件上的应用。 该项目将重点关注在与地幔相关的广泛范围的植物和氧气中，对地幔衍生的吡喃烯的收集电导率和热燃量的收集。 通过在几个氧赋形性状态下以电导率和电导率进行串联的热电器测量，可以估计变化荷载体的浓度和迁移率，并构建点缺陷模型，以扩展到扩展到更大范围的地幔条件。 橄榄石的不含量模型已成为与实验室实验进行比较的标准，并在最近的实验中反复验证。在过去的几年中，人们非常关注水对橄榄石电导率的影响。 但是，水分隔离量表表明，辉石可能持有的H2O ASOLIVINE的十倍。 除了有助于散装成分之外，在静脉区域发现了辉石（Rockswith 50％辉石），这是重要的地球化学预算，并且可能是中山山脊和海洋岛玄武岩中的“石榴石签名”。 如果这样的静脉互连网络，它们将具有不成比例的效应地幔电导率。 作为这项研究的一部分开发的可靠无水辉石电导率模型将有助于解释对含水辉石的未来电导率实验，并改善对地幔电导率的解释，这些地幔导率推断出源自电磁声音。