Transformations of Mg- and Ca-sulfate hydrates in Mars regolith
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and
Abstract
Salt hydrates have an active role in regolith development on Mars. The Mg-sulfate system, with highly variable values of n in the formula MgSO4·nH2O, is particularly subject to transformations among several crystalline and amorphous forms. The Ca-sulfate system, CaSO4·nH2O, is likely to be associated with the Mg-sulfates in most occurrences, but is less susceptible to transformations in n. Desiccation of MgSO4·nH2O occurs in exposed soils at the martian equator in summer where higher daytime temperatures at low relative humidity prevail against sluggish nighttime rehydration at high relative humidity. Desiccation and rehydration are both accelerated in the finest size fractions, particularly in silt-size aeolian particles subject to global redistribution by dust storms. This redistribution and periodic excursions into long-term episodes of high obliquity work to rehydrate desiccated MgSO4·nH2O to form epsomite, MgSO4·7H2O, at higher latitudes in the first case and more globally in the latter. Kieserite, a monohydrate form of MgSO4·nH2O resistant to desiccation, can survive equatorial summer conditions, but not protracted high relative humidity; preservation of kieserite at the surface may place limits on the equatorial distribution of ice during past episodes of high obliquity. Deeper horizons in equatorial regolith may preserve hydrated phases through repeated obliquity episodes, raising the possibility of an ancient regolith archive of past hydration. At shallower depths in the regolith, in situ determination of the hydration states of the Mg-sulfates, and possibly the Ca-sulfates, may be used to constrain regolith dynamics if rates and modes of transitions in n can be fully characterized.
© 2015 by Walter de Gruyter Berlin/Boston
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- Orbicular oxides in carbonatitic kimberlites
- Fluid-mediated polymetamorphism related to Proterozoic collision of Archean Wyoming and Superior provinces in the Black Hills, South Dakota
- Lithium isotopic systematics of granites and pegmatites from the Black Hills, South Dakota
- Identifying the effects of petrologic processes in a closed basaltic system using trace- element concentrations in olivines and glasses: Implications for comparative planetology
- Tectonic implications of diverse igneous blocks in Franciscan mélange, Northern California and southwestern Oregon
- The petrogenesis of the Apollo 14 high-Al mare basalts
- Experimental insights on crystal chemistry of high-Ti garnets from garnet-melt partitioning of rare-earth and high-field-strength elements
- The atomic arrangement of merrillite from the Fra Mauro Formation, Apollo 14 lunar mission: The first structure of merrillite from the Moon
- The behavior of Li and B in lunar mare basalts during crystallization, shock, and thermal metamorphism: Implications for volatile element contents of martian basalts
- Pyroxene europium valence oxybarometer: Effects of pyroxene composition, melt composition, and crystallization kinetics
- Comparative planetary mineralogy: Pyroxene major- and minor-element chemistry and partitioning of vanadium between pyroxene and melt in planetary basalts
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- An experimental study of trace-element partitioning between Ti-Al-clinopyroxene and melt: Equilibrium and kinetic effects including sector zoning
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- An experimental study of the oxidation state of vanadium in spinel and basaltic melt with implications for the origin of planetary basalt
- Valence state partitioning of vanadium between olivine-liquid: Estimates of the oxygen fugacity of Y980459 and application to other olivine-phyric martian basalts
- Identification of relict forsterite grains in forsterite-rich chondrules from the Mokoia CV3 carbonaceous chondrite
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- α-PbO2-type nanophase of TiO2 from coesite-bearing eclogite in the Dabie Mountains, China–Reply
- Rietveld structure refinement of perovskite and post-perovskite phases of NaMgF3 (Neighborite) at high pressures
- Letter. Si vacancies in the 10-Å phase
