High Pressure-Temperature Single-Crystal Elasticity of the Lower-Mantle Bridgmanite

地球的下地幔从670公里的深度一直延伸到2900公里深的地核-地幔边界。那里的压力和温度超过130万大气压和3500 K（5840华氏度）。了解它的性质对约束地球动力学至关重要。下地幔将热量从外核传导出去。这有助于为地球磁场提供能量，从而保护我们免受太阳风的影响。此外，地幔中的热对流驱动板块构造和相关的危险，如地震和火山爆发。地震学，研究地震波（弹性），可以直接观察下地幔结构。但他们的解释需要了解本构矿物的弹性特性。桥辉石占下地幔体积的3/4以上，是地球上储量最丰富的矿物。在研究下地幔性质时，这也是至关重要的。在这里，研究小组通过实验量化了桥菱石在地球深处极端条件下的弹性特性。结合高压设备和最先进的分析技术，它们提供了解释下地幔结构的数据；值得注意的是，大的神秘省份显示出低地震切变速度。该项目在地震学和地球动力学方面具有重要意义。它还为一些研究生和本科生提供矿物物理学方面的支持和培训，并向当地小学和中学提供教育推广。在这项研究中，研究小组在实验室中合成了含（Al,Fe）的大单晶菱镁石。研究了金刚石砧池在极端压力和温度条件下的晶体特性。这个装置在两个相对的钻石顶端产生高压。高温是通过外部加热或使用聚焦激光束获得的。利用实验室布里渊和脉冲受激光散射以及国家同步加速器设施的x射线衍射相结合，原位测量了晶体的弹性特性。这是可以实现的，因为该团队正在开发时间分辨脉冲激光光谱的新技术。这些新技术将与社区分享，用于未来极端条件下材料性能的研究。研究人员利用获得的数据来约束桥菱石的全弹性模量作为压力、温度及其在铁和铝中的含量的函数。将结果外推到与下地幔有关的条件，以及建模，可以解释地震学观测结果。该项目的成果是进一步了解地震速度、温度剖面和地球深处的化学成分。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

Earth's lower mantle extends from 670 km depth down to the core-mantle boundary, 2900 km deep. There, pressure and temperature exceed 1.3 million atm and 3500 K (5840 degree Fahrenheit). Understanding its properties is critical to constrain the planet dynamics. The lower mantle conducts heat away from the outer core. This contributes to power the Earth's magnetic field which shields us from the solar wind. Furthermore, thermal convection in the mantle drives plate tectonics and associated hazards, such as earthquakes and volcanic eruptions. Seismology, the study of seismic (elastic) waves, allows to observe directly the lower-mantle structures. But their interpretation requires knowledge of the elastic properties of the constitutive minerals. Bridgmanite accounts for more than 3/4th of the volume of the lower mantle, making it the most abundant mineral in the Earth. It is also of crucial interest when investigating lower-mantle properties. Here, the team quantifies experimentally the elastic properties of bridgmanite at the extreme conditions of the deep Earth. Coupling high pressure devices and state-of-the-art analytical techniques, they provide data allowing the interpretation of lower-mantle structures; notably that of large enigmatic provinces showing low seismic shear velocities. The project has strong implications in Seismology and broad impacts in Geodynamics. It also provides support and training in Mineral Physics for several graduate and undergraduate students, as well as educational outreach toward local elementary and middle schools. In this study, the team synthesize large single crystals of (Al,Fe)-bearing bridgmanite in the laboratory. Crystal properties are investigated at extreme conditions of pressure and temperature in the diamond-anvil cell. This apparatus generates high pressures at the tip of two opposing diamonds. The high temperatures are obtained by external heating or using focused laser beams. Crystal elastic properties are measured in situ using a combination of laboratory Brillouin and impulsive stimulated light scattering, as well as X-ray diffraction at national synchrotron facilities. This is achievable because the team is developing new technology in time-resolved impulsive laser spectroscopy. These new techniques will be shared with the community for future studies of material properties at extreme conditions. The researchers use the obtained data to constrain bridgmanite full elastic moduli as a function of pressure, temperature and of its contents in iron and aluminum. Extrapolation of the results to conditions relevant to the lower mantle, as well as modeling, allows interpreting seismological observations. The project outcomes further the understanding of seismic velocities, temperature profiles and chemical compositions in the deep Earth.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.