Core formation and geophysical properties of Mars
Core formation and geophysical properties of Mars
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DOI：
10.1016/j.epsl.2019.115923
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发表时间：
2020-01-15
影响因子：
5.3
通讯作者：
Irving, Jessica C. E.
中科院分区：
文献类型：
--
作者：
Brennan, Matthew C.;Fischer, Rebecca A.;Irving, Jessica C. E.
类地行星内部的化学和物理特性在很大程度上是在其形成和分化过程中决定的。对行星的形成进行建模可以提供对其核心和地幔特性的重要见解，相反，对这些特性的了解可能会限制形成的叙述。在这里，我们提出了火星核心形成的多阶段模型，其中我们使用高压高温金属硅酸盐分配实验的参数化来计算核心-地幔平衡。我们考虑了不断变化的核幔边界（CMB）条件、成分相关的分配以及金属和硅酸盐的部分平衡，并且我们自洽地演化出氧逸度（102）。该模型成功地再现了已发表的基于陨石的对大量硅酸盐火星中大多数元素丰度的估计，这可用于估计核心形成条件和核心成分。这种成分意味着，形成火星的原始物质比地球的氧化程度明显更高（比铁废料缓冲区低0.9-1.4个对数单位），并且火星的核-地幔平衡发生在演化的CMB压力的42-60%处。平均而言，每次撞击中至少有 84% 的增生金属和至少 40% 的地幔达到平衡，这比之前报道的地球金属平衡程度要高得多。与之前的研究一致，模拟的火星核心富含硫（18-19 wt%），0 重量百分比不到 1%，Si 可以忽略不计。我们使用这些核心和地幔成分来生成当今火星内部的物理模型，并评估核心半径对地壳厚度、地幔温度、核心成分、核心温度和核心合金密度的敏感性。这些属性如何影响可观测的物理参数（如行星质量、半径、转动惯量和潮汐乐夫数 k(2)）的权衡定义了可能的核心半径范围：1620-1870 公里。模型参数的几种组合的地震速度剖面已用于预测地震体波传播时间和行星简正模式频率。这些结果可以与即将发布的火星地震数据进行比较，以进一步限制岩心形成条件和地球物理特性。 (C) 2019 Elsevier B.V. 保留所有权利。
The chemical and physical properties of the interiors of terrestrial planets are largely determined during their formation and differentiation. Modeling a planet's formation provides important insights into the properties of its core and mantle, and conversely, knowledge of those properties may constrain formational narratives. Here, we present a multi-stage model of Martian core formation in which we calculate core-mantle equilibration using parameterizations from high pressure-temperature metal silicate partitioning experiments. We account for changing core-mantle boundary (CMB) conditions, composition-dependent partitioning, and partial equilibration of metal and silicate, and we evolve oxygen fugacity (102) self-consistently. The model successfully reproduces published meteorite-based estimates of most elemental abundances in the bulk silicate Mars, which can be used to estimate core formation conditions and core composition. This composition implies that the primordial material that formed Mars was significantly more oxidized (0.9-1.4 log units below the iron-wastite buffer) than that of the Earth, and that core-mantle equilibration in Mars occurred at 42-60% of the evolving CMB pressure. On average, at least 84% of accreted metal and at least 40% of the mantle were equilibrated in each impact, a significantly higher degree of metal equilibration than previously reported for the Earth. In agreement with previous studies, the modeled Martian core is rich in sulfur (18-19 wt%), with less than one weight percent 0 and negligible Si.We have used these core and mantle compositions to produce physical models of the present-day Martian interior and evaluate the sensitivity of core radius to crustal thickness, mantle temperature, core composition, core temperature, and density of the core alloy. Trade-offs in how these properties affect observable physical parameters like planetary mass, radius, moment of inertia, and tidal Love number k(2) define a range of likely core radii: 1620-1870 km. Seismic velocity profiles for several combinations of model parameters have been used to predict seismic body-wave travel times and planetary normal mode frequencies. These results may be compared to forthcoming Martian seismic data to further constrain core formation conditions and geophysical properties. (C) 2019 Elsevier B.V. All rights reserved.