Stability of micas on the surface of Venus

Recent thermodynamic modeling shows that some micas might be stable on Venussurface. However, prior studies considered only pure micas and did not consider mica solidsolutions, which are commonly observed on Earth. Here we use chemical equilibriumcalculations to evaluate the stability of mica solid solutions on Venus surface as a function ofatmospheric chemistry (H2O and HF abundances, and redox state), and surface elevation. Ourprior calculations show that the end-member micas eastonite (KMg2Al3Si2O10(OH)2) andfluorphlogopite (KMg3AlSi3O10F2) are stable on Venus surface, while the end-member micasphlogopite (KMg3AlSi3O10(OH)2), annite (KFe3AlSi3O10(OH)2), and siderophyllite (KFe2+2Al3Si2O10(OH)2) are unstable. Based on these results and known petrologic phase relationships, weconsider binary solutions of eastonite with either phlogopite or siderophyllite, andfluorphlogopite with phlogopite. We calculate that micas along all three binaries are stable onVenus. Micas containing ∼20 mole% eastonite and ∼80% phlogopite are stable in the lowertemperature highlands, and very eastonite-rich micas are stable over Venus entire surface.Fluorphlogopite-rich micas are also stable over Venus surface, while fluorphlogopite-poor micasare stable at higher elevations. Iron-poor micas along the eastonite-siderophyllite join, containing>80 mole% eastonite, are stable in both the highlands and lowlands. Finally, we use thethermodynamic calculations, terrestrial geology, and petrologic phase equilibria to discussplausible geological settings where micas may be present on Venus. These suggestions areimportant for the design of geochemical experiments on future lander and automated balloonmissions to Venus.