http://arxiv.org/abs/2208.09582
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 (Ghiorso et al. 1995) with gas-species properties from multiple thermochemistry tables (e.g. Chase et al. 1998). VapoRock calculates abundances 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 within a factor of ~3, consistent with measurement uncertainties. We also benchmark against a wide selection of igneous rock compositions including bulk silicate Earth, predicting elemental vapor abundances that are comparable (Na, Ca, & Al) or more realistic (K, Si, Mg, Fe, & Ti) than those of the closed-source MAGMA code (with maximum deviations by factors of 30-300 for K). Calculated vapor abundances depend critically on liquid activities, and the MELTS model underpinning VapoRock was specifically calibrated on natural igneous liquids and has been extensively tested & refined over the last 3 decades. In contrast, MAGMA’s underlying liquid model assumes ideal mixtures of liquid pseudo-species, which are incapable of capturing the non-ideal compositional interactions that typify the behavior of natural silicate melts. Using VapoRock, we finally 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.
A. Wolf, N. Jäggi, P. Sossi, et. al.
Tue, 23 Aug 22
6/79
Comments: N/A