Lower mantle seismic anisotropy and heterogeneities - insight from the thermoelastic properties of CaSiO3 perovskite

下地幔地震各向异性和异质性——从 CaSiO3 钙钛矿热弹性性质的洞察

• 批准号: 2240506
• 负责人: Jin Zhang
• 金额: $ 39.92万
• 依托单位: Texas A&M University
• 依托单位国家: 美国
• 项目类别: Continuing Grant
• 财政年份: 2023
• 资助国家: 美国
• 起止时间: 2023-02-15 至 2026-01-31
• 项目状态: 未结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=2240506&HistoricalAwards=false
• 关键词: Lower; mantle; seismic; anisotropy; heterogeneities

Growing evidence shows that the motions of mantle convection do not effectively mix the Earth’s deep interior, most notably at the top and the bottom of the lower mantle. Seismic observations show significant variations in both wave speeds and anisotropy, indicative of poor mixing of different rock types. One of the most important materials that may be responsible for these observations is calcium silicate perovskite, or CaSiO3. It is not only a major component of the ambient lower mantle, but also an important phase in the surface crustal materials that are transported into the lower mantle. Thus, estimating the amount of CaSiO3 throughout the Earth’s lower mantle can elucidate the material exchange process between the Earth’s interior and the surface. This requires measurement of the wave speeds through this mineral as a function of direction and minor element composition, which is the focus of this project. This work will also enable PI Zhang and her research group to develop a seminar course at Texas A&M University focusing on modern synchrotron experimental techniques used to the Earth and other planets from the surface to the interior. No similar class has been offered at Texas A&M University, and such class will open enable research opportunities for students, bringing potential users to synchrotron facilities, and training the next-generation researchers and scientists in US. High school students from underrepresented groups will be recruited to work with PI on research projects, promoting diversity of the geoscience community.This project will evaluate CaSiO3 perovskite (davemaoite, Ca-pv) as the potential candidate for explaining the observed seismic anisotropy and heterogeneities in the Earth’s lower mantle. The thermoelastic properties of cubic and tetragonal Ca-pv will be measured through Brillouin spectroscopy methods combined with diamond anvil cell technique. Due to the unquenchable nature of Ca-pv and the poor coupling between CaSiO3 and Nd:YAG laser with the 1024 nm wavelength, the sample will be synthesized in-situ using the CO2 laser heating method. Equation of state of Ca-pv will be determined using synchrotron X-ray diffraction. Utilizing the better constrained thermoelastic properties of cubic and tetragonal Ca-pv, PI Zhang and her group will evaluate the role of Ca-pv in the observed seismic heterogeneities in the lower mantle, as well as estimate the seismic anisotropy produced by Ca-pv after combining with textural measurements of Ca-pv.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.

越来越多的证据表明，地幔对流运动并不能有效地混合地球内部深处，尤其是在下地幔的顶部和底部，地震观测显示波速和各向异性存在显着变化，表明不同岩石的混合不良。可能对这些观测负责的最重要材料之一是硅酸钙钛矿（CaSiO3），它不仅是周围下地幔的主要成分，也是地幔中的重要相。因此，估算整个地球下地幔中 CaSiO3 的含量可以阐明地球内部和地表之间的物质交换过程，这需要测量通过这种矿物的波速。方向和微量元素组成的函数，这是该项目的重点，这项工作也将使 PI 张和她的研究小组能够在德克萨斯农工大学开发一门研讨会课程，重点关注用于地球的现代同步加速器实验技术。德克萨斯农工大学还没有开设过类似的课程，为学生提供研究机会，为同步加速器设施带来潜在用户，并培训美国下一代研究人员和科学家。来自代表性不足群体的高中生将被招募与 PI 一起开展研究项目，促进地球科学界的多样性。该项目将评估 CaSiO3 钙钛矿（davemaoite，Ca-pv）作为解释观察到的现象的潜在候选者。由于Ca-pv的不可淬灭性质以及CaSiO3和CaSiO3之间的不良耦合，将通过布里渊光谱方法结合金刚石砧池技术来测量地球下地幔的地震各向异性和不均匀性。 Nd:YAG激光波长为1024 nm，采用CO2激光加热状态方程法对样品进行原位合成。 Ca-pv 将使用同步加速器 X 射线衍射来确定，利用立方和四方 Ca-pv 更好的受约束热弹性特性，PI 张和她的团队将评估 Ca-pv 在观测到的下地幔地震不均匀性中的作用，以及结合 Ca-pv 的结构测量后估计 Ca-pv 产生的地震各向异性。该奖项反映了 NSF 的法定使命，并被认为值得支持使用基金会的智力价值和更广泛的影响审查标准进行评估。