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。深部地球材料的高压和高温弹性已被NSF COMPRES财团确定为一项重大挑战。地球所有主要边界层和内核中地震各向异性的存在，突显了矿物物理各向异性弹性数据的重要性。通过这一奖项，一台最先进的千兆赫超声波干涉仪将与下一代大体积宝石和化学气相沉积(CVD)金刚石顶锤压力室对接，努力获得一些与地球物理相关的地球形成矿物的准确热力学状态方程。高P-T实验将以PI开发的超声波方法的最新突破为特色，其中纯极化的超声波横波通过P-to-S转换传输到钻石-顶锤单元中。大型宝石顶锤充气技术的应用将极大地扩展超声波测量的工作P-T范围。这项研究中的超声波实验将集中在较暗的、含铁的硅酸盐、氧化物和金属，如环木石、镁闪锌矿和金属铁，因为这些材料的研究对现有的光学方法来说是有问题的。声波在单晶样品中的传播时间将被用来确定P波速度、S波速度、弹性波各向异性和完全弹性张量，由此可以很容易地确定绝热体积和剪切模数，以便与地震观测直接比较。最后，使用GHz技术将精确地确定CVD金刚石退火后的弹性张量，因为对单个弹性常数的了解将有助于表征新的砧座材料，并可能为CVD金刚石晶体非凡的机械性能的起源提供洞察。这项工作将促进地球物理实验室和德国拜罗伊特的巴耶里斯地质研究所之间的合作，包括至少一名研究生和可能参加卡内基研究所暑期实习方案的几名本科生，该方案部分由国际地球物理研究所管理。

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.