Vaporization and thermodynamics of forsterite-rich olivine and some implications for silicate atmospheres of hot rocky exoplanets
Vaporization and thermodynamics of forsterite-rich olivine and some implications for silicate atmospheres of hot rocky exoplanets
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DOI：
10.1016/j.icarus.2017.02.006
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发表时间：
2017-06-01
期刊：
影响因子：
3.2
通讯作者：
Fegley, Bruce, Jr.
中科院分区：
文献类型：
--
作者：
Costa, Gustavo C. C.;Jacobson, Nathan S.;Fegley, Bruce, Jr.
本文描述了橄榄石[Mg2SiO4 (Fo)-Fe2SiO4 (Fa)]汽化的实验和理论研究。在1750 ~ 2250K范围内，用高温Knudsen液质谱（KEMS）研究了富培养石橄榄石(Fo（95)Fa(5)）的汽化行为和热力学性质。观察到的气体（按分压递减的顺序）分别是Fe、SiO、Mg、O-2和o。我们测量了固相温度（类似于2050K）、各个气体的分压、总蒸汽压以及Fo(95)Fa(5)橄榄石的MgO、FeO和SiO2的热力学活度和偏摩尔焓。结果与其他测量结果和橄榄石体系的模型进行了比较。我们的实验数据表明橄榄石的蒸发是不一致的。我们将该体系作为Fo-Fa的准二元体系和MgO-'FeO'- sio2的准三元体系来讨论。样品中铁/镁的摩尔比在气化前（类似于0.05）和气化后（类似于0.04）与所研究的组成（例如，Nafziger和Muan， 1967）中橄榄石中铁/镁的理想值（γ类似于1.17）的小正偏差是一致的。我们关于橄榄石+熔体的数据证实了先前的理论模型，该模型预测熔融硅酸盐中Fe相对于Mg的部分汽化（Fegley和Cameron, 1987； Schaefer和Fegley, 2009； Ito等人，2015）。如果硅酸盐大气的损失发生在具有岩浆海洋的热岩系外行星上，那么残留的行星可能相对于铁富含镁。(C) 2017爱思唯尔公司版权所有。
We describe an experimental and theoretical study of olivine [Mg2SiO4 (Fo)-Fe2SiO4 (Fa)] vaporization. The vaporization behavior and thermodynamic properties of a fosterite-rich olivine (Fo(95)Fa(5)) have been explored by high-temperature Knudsen effusion mass spectrometry (KEMS) from 1750 to 2250K. The gases observed (in order of decreasing partial pressure) are Fe, SiO, Mg, O-2 and O. We measured the solidus temperature (similar to 2050K), partial pressures of individual gases, the total vapor pressure, and thermodynamic activities and partial molar enthalpies of MgO, 'FeO', and SiO2 for the Fo(95)Fa(5) olivine. The results are compared to other measurements and models of the olivine system. Our experimental data show olivine vaporizes incongruently. We discuss this system both as a psuedo-binary of Fo-Fa and a psuedo-ternary of MgO-'FeO'-SiO2. Iron/magnesium molar ratios in the sample before (similar to 0.05) and after (similar to 0.04) vaporization are consistent with the small positive deviations from ideality of fayalite (gamma similar to 1.17) in olivine of the composition studied (e.g., Nafziger and Muan, 1967). Our data for olivine+melt confirm prior theoretical models predicting fractional vaporization of Fe relative to Mg from molten silicates (Fegley and Cameron, 1987; Schaefer and Fegley, 2009; Ito et al., 2015). If loss of silicate atmospheres occurs from hot rocky exoplanets with magma oceans the residual planet may be enriched in magnesium relative to iron. (C) 2017 Elsevier Inc. All rights reserved.