Elasticity and Spin Transitions of Iron in the Earth's Lower Mantle

地幔是一个约2900公里厚的硅酸盐岩石壳，约占地球体积的84%。它进一步分为三个层，上地幔，过渡带和下地幔，作为橄榄石多晶型物的结构相变的结果。深度为670 ~ 2900 km的下地幔主要由硼镁石（硅酸盐钙钛矿）和铁方镁石组成，其中铁是最丰富的过渡金属。深地科学家最近发现，这些下地幔矿物中铁的自旋跃迁会对宿主矿物的物理、化学和输运性质产生一系列影响。因此，研究下地幔矿物在铁自旋跃迁过程中的声速分布可以帮助我们了解该地区的化学和物理。本项目以自旋跃迁效应为重点，旨在广泛了解下地幔矿物在相关压力-温度-成分条件下的热弹性，提供直接的矿物物理结果和热力学数据库，以便与地震层析图像、地球化学分析和地幔地球动力学模型相结合。将通过模拟铁方镁石和硼镁石中铁的热弹性和分配系数，沿沿着预期的下地幔地热，研究下地幔自旋转变的地球物理和地球化学后果。这些结果将有助于检验地震波剖面的假设，阐明铁的化学成分及其组成模型，并确定地球深部地幔的动力学行为。拟议的矿物物理学研究使用同步加速器X射线和内部激光光谱在金刚石砧室，旨在探测地幔矿物的结构和弹性特性在压力-温度条件下的地球地幔。在该项目的倡议下，学生和博士后研究人员将有独特的研究机会，使用先进的同步加速器X射线设施在先进的光子源和激光光谱在得克萨斯大学奥斯汀分校获得所需的实验室结果破译地震和地球化学观测地球的下地幔。这些活动将有助于教育下一代对地球深层内部有透彻了解的独立研究人员。在这个项目中的推广活动的重点是暴露代表性不足的K-12年级的深地球研究，让他们参与夏季外展计划。该奖项的研究成果将通过教学，研讨会，会议和同行评审的出版物广泛传播。拟议的工作通过使用共享设施和发展不同领域研究人员之间的新合作来加强研究和教育的基础设施。该项目将为学生和博士后研究人员提供与地震学，地球动力学和地球化学多学科领域的科学家合作的绝佳机会。

Earth's mantle is a silicate rocky shell about 2900 km thick that constitutes approximately 84% of the planet's volume. It is further separated into three layers, upper mantle, transition zone, and lower mantle, as a result of the structural phase transitions of the olivine polymorphs. The lower mantle ranging from 670 km to 2900 km in depth is mainly made of bridgmanite (silicate perovskite) and ferropericlase in which iron is the most abundant transition metal. Deep-Earth scientists have recently discovered that the spin transitions of iron in these lower-mantle minerals can have a series of effects on physical, chemical, and transport properties of the host minerals. Studying the sound velocity profiles of the lower-mantle minerals across the spin transition of iron can thus help us understand the chemistry and physics of the region. With an emphasis on the effects of the spin transitions, this project aims broadly to understand thermal elasticity of the lower-mantle minerals at relevant pressure-temperature-composition conditions, providing direct mineral physics results and thermodynamic database to be integrated with seismic tomographic images, geochemical analyses, and geodynamic models of the mantle. The geophysical and geochemical consequences of the spin transition in the lower mantle will be examined through modelling the thermal elasticity and the partitioning coefficient of iron in ferropericlase and bridgmanite along an expected lower-mantle geotherm. These results will help test hypotheses on seismic wave profiles, elucidate the chemistry of iron and its compositional model, and determine the dynamic behavior of the Earth's deep mantle.The proposed mineral physics research uses synchrotron X-ray and in-house laser spectroscopies in a diamond anvil cell designed to probe structural and elastic properties of the mantle minerals at pressure-temperature conditions of the Earth's mantle. Under the initiatives of the project, students and postdoctoral researchers will have unique research opportunities to use advanced synchrotron X-ray facilities at the Advanced Photon Source and laser spectroscopies at the University of Texas at Austin to obtain laboratory results needed to decipher seismic and geochemical observations of the planet's lower mantle. These activities will contribute to the education of the next generation of independent researchers with a thorough knowledge of the Earth's deep interior. Outreach activities in this project focus on exposing underrepresented K-12th graders to deep-Earth research by involving them in the outreach summer programs. Research results from this award will be disseminated broadly through teaching, seminars, conferences, and peer-reviewed publications. The proposed work enhances infrastructure for research and education by using shared facilities and the development of new collaborations among researchers in different fields. The project will provide students and postdoc researchers with a great opportunity to collaborate with scientists in the multidisciplinary fields of seismology, geodynamics, and geochemistry.