Single-crystal elasticity of martian mantle minerals and a flexible CO2 laser heating system

火星地幔矿物的单晶弹性和灵活的二氧化碳激光加热系统

• 批准号: 411764160
• 负责人: Dr. Alexander Kurnosov
• 金额: --
• 依托单位: Bayerisches Forschungsinstitut für Experimentelle Geochemie und Geophysik (BGI)
• 依托单位国家: 德国
• 项目类别: Research Grants
• 财政年份: 2018
• 资助国家: 德国
• 起止时间: 2017-12-31 至 2021-12-31
• 项目状态: 已结题
• 来源: https://gepris.dfg.de/gepris/projekt/411764160?language=en
• 关键词: Single; crystal; elasticity; martian; mantle

Observations of the seismic wave velocity structure of the Martian interior are becoming increasingly available from the SEIS seismometer on the NASA InSight lander. The interpretation of such data relies crucially on the ability to model the mineralogy and seismic velocities of the Martian interior in order to test plausible compositions and temperature gradients. To date, however, such models for the Martian mantle are constructed using thermodynamic parameters that are either estimated, not determined from the most recent phase equilibria and elasticity data or are not suitable for determining Martian compositions. Very few elasticity measurements exist at simultaneous high pressure and temperature conditions, requiring data for most minerals to be extrapolated to some extent, which introduces significant uncertainties.In the first period of this project a new system was developed to measure acoustic wave velocities at pressures and temperatures corresponding to the entire Martian mantle. The system, where Brillouin spectroscopy measurements are performed simultaneously with CO2-laser heating in a diamond anvil cell, has been successfully benchmarked by performing measurements on single crystals of pyrope. By combining these data with further measurements on Fe-rich ringwoodite and recent data from the literature, an updated mineral-physics model for the base of the Martian mantle has been obtained. Significant differences exist with previous models based on properties of terrestrial materials. Using the new model to interpret a proposed Martian mantle discontinuity at 1140 km, implies a temperature at this depth in the range 1870-1970 K. In the renewal phase, simultaneous single crystal X-ray diffraction measurements will be also implemented, to obtain a truly unique system capable of determining the full elastic tensor of any mineral throughout the conditions of any terrestrial planet. Using this system, the determination of the full elastic tensors of the main Martian minerals will be completed by examining Fe-rich single crystals of majoritic garnet, olivine and even the low symmetry mineral clinopyroxene, at pressures and temperatures of their stability in the Martian mantle. These data will be used to develop a an internally consistent thermodynamic model to predict the mineralogy and seismic wave velocities of the Martian mantle with vastly reduced uncertainties. This model will not only be used to interpret the emerging observations of Martian seismic structure and assess the uncertainties in these interpretations, but will also provide a first assessment of how seismic anisotropy has the potential to influence observations of the Martian interior. Moreover, by studying minerals comprised of different solid solution components, we will address a central issue in mineral physics as to whether the properties of intermediate compositions can be effectively described using linear combinations of end member properties.

从NASA Insight着陆器上的SEIS地震仪可以越来越多地观察到火星内部的地震波速度结构。对这些数据的解释主要依赖于对火星内部的矿物学和地震速度进行建模的能力，以便测试可信的成分和温度梯度。然而，到目前为止，火星地幔的这种模型是使用热力学参数构建的，这些热力学参数要么是估计的，不是根据最新的相平衡和弹性数据确定的，要么是不适合确定火星成分的。在高压和高温同时存在的情况下，很少有弹性测量，这需要对大多数矿物的数据进行一定程度的外推，这带来了显著的不确定性。在该项目的第一阶段，开发了一个新的系统来测量与整个火星地幔对应的压力和温度下的声波速度。该系统的布里渊光谱测量是在金刚石顶压室中与CO2激光加热同时进行的，该系统已经通过对镁铝榴石单晶的测量成功地进行了基准测试。通过将这些数据与对富铁环木岩的进一步测量和文献中的最新数据相结合，得到了一个更新的火星地幔底部矿物物理模型。根据陆地材料的性质，与以前的模型存在显著差异。使用新的模型来解释所提出的1140公里处的火星地幔不连续面，意味着在这个深度的温度范围在1870-1970年K。在更新阶段，还将实施同步的单晶X射线衍射测量，以获得一个真正独特的系统，能够在任何类地行星的条件下确定任何矿物的全部弹性张量。利用这一系统，在火星地幔稳定的压力和温度下，通过检查主要石榴石、橄榄石甚至低对称性矿物单斜辉石的富铁单晶，就可以完成对主要火星矿物的全弹性张量的测定。这些数据将被用来开发一个内部一致的热力学模型，以预测火星地幔的矿物学和地震波速度，并大大减少不确定性。该模型不仅将用于解释对火星地震结构的新兴观测，并评估这些解释中的不确定性，还将首次评估地震各向异性如何潜在地影响对火星内部的观测。此外，通过研究由不同固溶体组成的矿物，我们将解决矿物物理学中的一个中心问题，即是否可以使用端元属性的线性组合来有效地描述中间组成的性质。