Elasticity of clinopyroxene (Ca, Na) (Mg, Al, Fe) Si2O6 under Earth's upper mantle conditions

地球上地幔是地球上最具活力的层之一，与许多对人类造成不利影响的构造过程密切相关。例如，俯冲和剥离是将地壳物质循环到地球深处的两个主要地质过程，可能导致地球内部的地震不均一性和各向异性，以及地球表面的破坏性地震和火山爆发。因此，了解地球上地幔的性质和动力学不仅对研究地幔组成和对流至关重要，而且与社会有关。由于直接采样的困难，地震学提供了迄今为止最准确的地球上地幔图像。有关矿物的声速和密度测量对于理解上地幔地震观测是必不可少的。单斜辉石是地球上地幔的主要矿物相(体积分数为10-30%)和榴辉岩的主要矿物(体积分数约为60-70%)，是地球内部最重要但研究最少的矿物群之一。榴辉岩密度高，被广泛认为是俯冲和拆沉的主要驱动力。因此，为了计算地球内部榴辉岩的浮力，需要在高压(P)-温度(T)条件下直接测量单斜辉石的密度。此外，单斜辉石是地球上地幔中最具各向异性的主要矿物。它也是造成榴辉岩各向异性的唯一相。对地震观测到的上地幔各向异性的解释需要了解单斜辉石在真实地球P-T条件下的单晶弹性。以前的实验研究主要局限于高对称性材料，如石榴石，其P-T条件远远低于地球内部预期的条件。这项研究的目的是现场测量单斜辉石的密度和单晶弹性，在新墨西哥大学实施完成拟议实验所需的光学系统，将所获得的实验结果应用于真实的地球，并为研究生和本科生，特别是未被充分代表的少数民族学生创造独特的机会，参与校园和国家实验室最先进的实验设施的科学研究。调查人员将使用同步加速器单晶显微衍射和单晶布里渊光谱结合CO2激光加热或电阻加热方法，系统地研究不同化学组成的单斜辉石在1800K和18 GPa时的热弹性性质(包括密度和单晶弹性)，覆盖地球上地幔的整个稳定场。所获得的实验结果将用于辅助地震解释和地球动力学模拟，这最终将有助于我们理解在地球上地幔观察到的各向异性和非均质性的起源和性质。

The Earth's upper mantle is one of the most dynamic layers of our planet and closely related to many tectonic processes adversely affecting human beings. For example, subduction and delamination, which are the two major geological processes of recycling crustal materials into the deep Earth, can result in seismic heterogeneities and anisotropies in the Earth's interior, as well as destructive Earthquakes and volcanisms on the Earth's surface. Therefore, understanding the nature and dynamics of the Earth's upper mantle is not only crucial for studying the mantle composition and convection but also relevant to society. Due to the difficulties of direct sampling, seismology provides by far the most accurate image of the Earth's upper mantle. Sound velocity and density measurements of relevant minerals are essential for understanding upper mantle seismic observations. Clinopyroxene, as a major phase of the Earth's upper mantle (10-30 vol%) and the dominating mineral of eclogite (about 60-70 vol%), is one of the most important yet least studied groups of minerals of the Earth's interior. Eclogite is widely believed to be the main driving force for subduction and delamination because of its high density. Thus direct density measurements of clinopyroxene at high pressure (P)-temperature (T) conditions are needed for calculating the buoyancy of eclogite in the Earth's interior. In addition, clinopyroxene is the most anisotropic major mineral in the Earth's upper mantle. It is also the only phase that contributes to any observed anisotropy of eclogite. Explanation of seismically observed upper mantle anisotropy requires knowledge of single-crystal elasticity of clinopyroxene at real Earth P-T conditions. Previous experimental studies have been limited mainly to high-symmetry materials, such as garnet, under P-T conditions far less than those expected in the Earth's interior. The purpose of this study is to measure the density and single-crystal elasticity of clinopyroxene in-situ, implement the optical system that is needed to complete the proposed experiments at University of New Mexico, apply the obtained experimental results to real Earth, and create unique opportunities for graduate and undergraduate students, especially underrepresented minority students, to participate in scientific research at the state-of-the-art experimental facilities both on campus and at national laboratories.The investigators will use synchrotron single-crystal micro-diffraction and single-crystal Brillouin spectroscopy combined with CO2 laser heating or resistive heating methods to systematically investigate the thermoelastic properties (including density and single-crystal elasticity) of clinopyroxene with different chemical compositions up to 1800K and 18 GPa, covering the entire stability field in the Earth's upper mantle. The obtained experimental result will be used to assist seismic interpretation and geodynamical modeling, which will eventually contribute to our understanding of the origin and nature of the anisotropy and heterogeneity observed in the Earth's upper mantle.