Other
Scientific paper
Dec 2009
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2009agufm.p13a1252n&link_type=abstract
American Geophysical Union, Fall Meeting 2009, abstract #P13A-1252
Other
[1034] Geochemistry / Hydrothermal Systems, [1039] Geochemistry / Alteration And Weathering Processes, [8445] Volcanology / Experimental Volcanism, [8450] Volcanology / Planetary Volcanism
Scientific paper
A question of major relevance to the assessment of habitability of the Martian crust is to what extent hydrothermal activity could have produced the alteration assemblages identified on the surface. This study focuses specifically on the possible role of magmatic fluids in producing these assemblages. Evidence for magmatic fluids is found in melt inclusions of several SNC Meteorites. Potassic jarosite (intergrown with hematite and goethite) has been found along with potassic chlor-hastingsite in a pyroxene-hosted melt inclusion of MIL 03346. It provides evidence for magmatic fluid that was retained as the rock cooled to below 200οC. Hydrothermal chlor-hastingsite with high chlorine contents (~1.8 sfu) suggests high chlorinity and relatively low water content of this fluid. The melt-inclusion jarosite contains significant Fe and only a small proportion of Al (0.10 sfu) in the M-site in spite of the presence of significant available Al (as evidenced by the presence of aluminous Fe-Si glass). This suggests that the parental liquids were dominated by Fe and that the pH of the parental aqueous phase was too low to facilitate hydrolysis of Al. The assemblage observed suggests that magmatic fluids on Mars can produce oxidized S-and Fe-rich assemblage. Although the late-stage mineral assemblages can provide insights into the evolution of the fluid, little evidence remains of the nature of the initial fluid composition and the minerals and/or melt with which it was in equilibrium, or of the nature of alteration minerals it would produce if interacting with Martian wallrock. Experiments are ongoing to define the chemistry of such fluids. They involve using a synthetic melt of composition of Backstay that has evolved to pyroxene saturation with 1.5 wt% Cl, 0.3 wt% S, and 0.3 wt% water. When crystallized at 50MPa, the melt becomes fluid-saturated during crystallization and the magmatic minerals associated with this fluid define the composition of the fluid. “Three-stage” experiments were designed to (i) melt the starting material above the liquidus temperature, (ii) allow the melt to crystallize slightly above the solidus temperature, and (iii) allow the exsolved fluid to back-react with the minerals in the subsolidus regime. Data on the magmatic and alteration assemblages provide insights into compositional evolution of the fluid with decreasing temperature.
McCubbin F.
Nekvasil Hanna
Ustunisik G. K.
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