Open AccessFormation of silica by low‐temperature acid alteration of Martian rocks: Physical‐chemical constraints
Author(s) -
McAdam Amy C.,
Zolotov Mikhail Y.,
Mironenko Mikhail V.,
Sharp Thomas G.
Publication year - 2008
Publication title -
journal of geophysical research: planets
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.67
H-Index - 298
eISSN - 2156-2202
pISSN - 0148-0227
DOI - 10.1029/2007je003056
Subject(s) - geology , dissolution , igneous rock , saturation (graph theory) , mineralogy , martian , dissolved silica , mars exploration program , aqueous solution , geochemistry , chemical engineering , chemistry , astrobiology , physics , mathematics , combinatorics , engineering
Theoretical geochemical modeling has been used to evaluate the formation conditions of amorphous silica during aqueous alteration of typical Martian igneous rocks at 0°C. The models show that some silica can form during low‐temperature alteration of mafic to ultramafic rocks over a large range of pH and water/rock ratios. Silica‐dominated deposits, like those found at the Columbia Hills in Gusev crater on Mars, could form at solution pH below ∼2 and water/rock ratios of ∼10 2 –10 4 . High‐water/rock conditions could represent acid flow through rocks, solution discharge from an acid spring, and/or surface flow of released solutions. Low pH favors dissolution of silicates and saturation of solution with respect to relatively insoluble silica, which then precipitates. Partial evaporation or freezing of released solutions would also cause precipitation of amorphous silica. Modeling shows that Ti oxides are also present in silica‐rich deposits. More soluble minerals (e.g., ferric oxides, phyllosilicates) could precipitate downstream from partially neutralized, evaporated, or frozen solutions. Temperatures above ∼0°C are not required to form abundant silica through acid alteration of Martian rocks.