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.

通过 NASA InSight 着陆器上的 SEIS 地震仪，对火星内部地震波速度结构的观测越来越多。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，以便测试合理的成分和温度梯度。然而，迄今为止，火星地幔的此类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，要么不适合确定火星的成分。在同时高压和高温条件下存在的弹性测量很少，需要在一定程度上外推大多数矿物的数据，这引入了很大的不确定性。在该项目的第一阶段，开发了一种新系统来测量压力和温度下的声波速度。相当于整个火星地幔的温度。该系统在金刚石砧室中同时进行布里渊光谱测量和二氧化碳激光加热，并通过对镁铝榴石单晶进行测量，成功地进行了基准测试。通过将这些数据与对富铁尖晶橄榄岩的进一步测量以及文献中的最新数据相结合，获得了火星地幔底部的最新矿物物理模型。与之前基于陆地材料特性的模型存在显着差异。使用新模型来解释拟议的 1140 km 处的火星地幔不连续性，意味着该深度的温度在 1870-1970 K 范围内。在更新阶段，还将实施同步单晶 X 射线衍射测量，以获得真正独特的系统，能够在任何类地行星的条件下确定任何矿物的完整弹性张量。使用该系统，将通过检查主要石榴石、橄榄石甚至低对称性矿物单斜辉石在火星地幔中的稳定性压力和温度下的富铁单晶来完成对主要火星矿物的全弹性张量的测定。这些数据将用于开发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，并大大降低不确定性。该模型不仅将用于解释火星地震结构的新兴观测结果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影响火星内部的观测结果。此外，通过研究由不同固溶体成分组成的矿物，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性质的线性组合有效地描述中间组合物的性质。