High P-T Elasticity of Deep Earth Materials With New Gigahertz-Ultrasonic Techniques

这项研究旨在通过实验了解地球内部的构成。深地材料的高压和高温弹性已被NSF COMPRES联盟确定为一个重大的大挑战。地球所有主要边界层和内核中地震各向异性的存在突出了矿物物理各向异性弹性数据的重要性。通过该合同，最先进的千兆赫超声干涉仪将与下一代大体积、宝石和化学气相沉积（CVD）钻石顶压单元相连接，以努力获得一些地球物理学上相关的地球形成矿物的精确热力学状态方程。高P-T实验将以PI开发的超声波方法的最新突破为特色，其中纯极化超声波剪切波通过p - s转换传输到金刚石砧细胞中。采用大型宝石砧的气体加载技术将大大扩展超声测量的工作P-T范围。本研究的超声实验将集中在颜色较深、含铁的硅酸盐、氧化物和金属，如菱辉石、菱镁砂和金属铁，因为对这些材料的研究对于现有的光学方法来说是有问题的。单晶样品中的声波传播时间将用于确定纵波速度，横波速度，弹性波各向异性和完全弹性张量，从中可以很容易地确定绝热体和剪切模量，以便与地震观测直接比较。最后，将使用ghz技术精确地确定退火CVD金刚石的弹性张量，因为单个弹性常数的知识将有助于表征新的砧材料，并可能为CVD金刚石晶体非凡机械性能的起源提供见解。这项工作将促进地球物理实验室和德国拜罗伊特的Bayerisches地质研究所之间的合作，涉及至少一名研究生和可能的几名本科生实习生参加卡内基研究所暑期实习计划，该计划部分由PI管理。

This study is aimed towards understanding the constitution of Earth's interior through experiment. The high-pressure and high-temperature elasticity of deep-Earth materials has been identified as a major Grand Challenge by the NSF COMPRES consortium. The presence of seismic anisotropy within all of Earth's major boundary layers and inner core highlights the importance of anisotropic elasticity data from mineral physics. Through this award, a state-of-the-art gigahertz-ultrasonic interferometer will be interfaced with the next generation of large-volume, gem and chemical vapor deposition (CVD) diamond-anvil pressure cells in an effort to obtain accurate thermodynamic equations of state for some geophysically relevant Earth-forming minerals. The high P-T experiments will feature a recent breakthrough in ultrasonic methods developed by the PI, wherein purely-polarized ultrasonic shear waves are transmitted into the diamond-anvil cell using a P-to-S conversion. The employment of gas-loading techniques with large gem anvils will greatly extend the working P-T range over which ultrasonic measurements can be made. The ultrasonic experiments in this study will focus on the darker, Fe-bearing silicates, oxides and metals such as ringwoodite, magnesiowustite, and metallic iron because the study of these materials is problematic for existing optical methods. Acoustic-wave travel times in single-crystal samples will be used to determine P-wave velocity, S-wave velocity, elastic-wave anisotropy and the complete elastic tensor, from which the adiabatic bulk and shear moduli are readily determined for direct comparison with seismological observation. Finally, the elastic tensor of annealed CVD diamond will be accurately determined using the GHz-technique because knowledge of the individual elastic constants will help to characterize the new anvil material and may provide insight into the origin of the extraordinary mechanical properties of CVD diamond crystals. This work will nurture collaborations between the Geophysical Laboratory and the Bayerisches Geoinstitut in Bayreuth, Germany, involving at least one graduate student and possibly several undergraduate interns attending the Carnegie Institution Summer Internship Program, which is managed in part by the PI.