VapoRock: Thermodynamics of Vaporized Silicate Melts for Modeling Volcanic Outgassing and Magma Ocean Atmospheres
VapoRock: Thermodynamics of Vaporized Silicate Melts for Modeling Volcanic Outgassing and Magma Ocean Atmospheres
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DOI：
10.3847/1538-4357/acbcc7
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发表时间：
2022-08
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影响因子：
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通讯作者：
A. Wolf;N. Jäggi;P. Sossi;D. Bower
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文献类型：
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作者：
A. Wolf;N. Jäggi;P. Sossi;D. Bower
硅酸盐蒸汽在行星演化中起着关键作用，特别是在岩石行星形成的早期阶段，通过排出的岩浆海洋大气层。我们的开源热力学建模软件“VapoRock”将MELTS液体模型与来自多个热化学表的气体种类属性相结合。VapoRock计算了Si-Mg-Fe-Al-Ca-Na-K-Ti-Cr-O系统中在所需温度和氧逸度（fO 2或O2分压）下与岩浆液体平衡的34种气体物质的分压。与实验的比较表明，压力和熔体氧化物的活动（在许多数量级上变化）被复制到一个因子的10.3，与测量不确定性一致。我们还基准的模型对广泛选择的火成岩成分，包括散装硅酸盐地球，预测元素蒸气丰度是可比的（钠，钙，铝）或更现实的比（K，硅，镁，铁，钛）的闭源MAGMA代码（与K和硅的最大偏差的10-300倍）。蒸汽丰度主要取决于液体组分的活动。支撑VapoRock的MELTS模型在天然火成岩液体上进行了校准和广泛测试。相比之下，MAGMA的液体模型假设一组有限的化学简化的赝物种的理想混合物，这只是粗略地近似的非理想成分的相互作用典型的多组分天然硅酸盐熔体。最后，我们探讨如何相对丰富的SiO和SiO2提供了一个光谱可测量的代理氧逸度脱挥发的系外行星大气，可能会限制氧在脱气的系外行星地幔。
Silicate vapors play a key role in planetary evolution, especially dominating early stages of rocky planet formation through outgassed magma ocean atmospheres. Our open-source thermodynamic modeling software “VapoRock” combines the MELTS liquid model with gas-species properties from multiple thermochemistry tables. VapoRock calculates the partial pressures of 34 gaseous species in equilibrium with magmatic liquid in the system Si–Mg–Fe–Al–Ca–Na–K–Ti–Cr–O at desired temperatures and oxygen fugacities (fO2, or partial pressure of O2). Comparison with experiments shows that pressures and melt-oxide activities (which vary over many orders of magnitude) are reproduced to within a factor of ∼3, consistent with measurement uncertainties. We also benchmark the model against a wide selection of igneous rock compositions including bulk silicate Earth, predicting elemental vapor abundances that are comparable to (Na, Ca, and Al) or more realistic than (K, Si, Mg, Fe, and Ti) those of the closed-source MAGMA code (with maximum deviations by factors of 10–300 for K and Si). Vapor abundances depend critically on the activities of liquid components. The MELTS model underpinning VapoRock was calibrated and extensively tested on natural igneous liquids. In contrast, MAGMA’s liquid model assumes ideal mixtures of a limited set of chemically simplified pseudospecies, which only roughly approximates the nonideal compositional interactions typical of many-component natural silicate melts. Finally, we explore how relative abundances of SiO and SiO2 provide a spectroscopically measurable proxy for oxygen fugacity in devolatilized exoplanetary atmospheres, potentially constraining fO2 in outgassed exoplanetary mantles.