Abstract
We used thermochemical equilibrium calculations to predict stabilities
of pure rock-forming hydrous silicates on Venus' surface as a function
of elevation, atmospheric H2O and SO2 concentrations, and oxygen
fugacity (fo(2),), About 50 different hydrous silicates were included
in our calculations. We find that many of these are unstable on Venus's
surface because of the low atmospheric H,O-2 content of 30-45 parts
per million by volume (ppmv) and the high surface temperatures (660
K on Maxwell Montes to 740 K in the plains), Hydrous Fe2+-bearing
silicates are unstable due to oxidation to magnetite and/or hematite
at the fo(2) Of the near-surface atmosphere. Ca-bearing hydrous silicates
are unstable because of sulfatization to anhydrite, Some Fe-free
micas (e.g.,, eastonite, eastonite-phlogopite micas), and some alkali
amphiboles might be stable on Venus' surface, especially in the lower
temperature highlands, We discuss hydrous mineral formation in the
interior and on the surface of Venus. We review the literature on
mica and amphibole thermal decomposition and find that dehydration
of phlogopitic micas and fibrous amphiboles produces (metastable)
dehydroxylated anhydrides that decompose to more stable minerals
at temperatures hundreds of degrees higher than the onset of dehydroxylation,
These observations raise the possibility that anhydrides formed from
hydrous silicates, which may have been present during a wetter period
in Venus' history, may persist somewhere on Venus' present surface.
We discuss experiments that could be used on future spacecraft missions
to detect hydroxyl in rocks and hydrous silicates on Venus, Finally,
we review estimates of the amount of water and OH (hydroxyl) in the
Earth's mantle. Based on this review, we suggest that even if no
hydrous silicates are stable on Venus, significant amounts of water
are plausibly present in surface rocks as OH in nominally anhydrous
minerals, (C) 1997 Academic Press.
Users
Please
log in to take part in the discussion (add own reviews or comments).