HR: 14:40h
AN: V23D-05    [Abstracts]
TI: Modelling Sulfur Content in Volcanic Gases of Mars
AU: Scaillet, B
EM: bscaille@cnrs-orleans.fr
AF: ISTO CNRS, Institut des Sciences de la Terre d'Orléans (ISTO), UMR 6113 CNRS, 1A rue de la Ferollerie, 45071 Orléans CEDEX 2, France, Orléans, 45071, France
AU: * Gaillard, F
EM: gaillard@cnrs-orleans.fr
AF: ISTO CNRS, Institut des Sciences de la Terre d'Orléans (ISTO), UMR 6113 CNRS, 1A rue de la Ferollerie, 45071 Orléans CEDEX 2, France, Orléans, 45071, France
AB: Both landed experiments and remote sensing instruments on spacecraft sent to Mars have shown the Martian regolith to be uniformly rich in sulphur, with abundances typically exceeding 2 orders of magnitude those of common sedimentary or igneous rocks on Earth. Various hypotheses have been put forward to explain such an enrichment, including remnants of primitive chondritic material during accretion and volcanic degassing, but none has been quantitatively evaluated. Here, by performing thermodynamic calculations on sulphur partitioning between molten iron core and magma ocean, we show that the Martian mantle has a sulphur content at least 3-4 times higher than that of its Earth counterpart due to more oxidant conditions during core-mantle separation. The high FeO content of the martian basalts implies that although sulphur-rich, these magma are not sulphide saturated at depth. As a result, partial melting of Martian mantle yields basaltic magmas with 3-10 times more sulphur than those of primitive mid-ocean ridge basalts on Earth. Calculations of gas compositions in equilibrium with Martian and Earth like basalts (MORB) at near surface conditions show that volcanic gases on Mars have 10-100 times more sulphur than those on Earth. In addition, the lower pressure of lava delivery on Mars relative to Earth suggests that Martian volcanic exhalations, although equilibrated under low fO2 conditions, may have been dominated by SO2 not H2S, ie unlike those on Earth. Higher sulphur contents and SO2 scrubbing by aquifers, both may have produced widespread acidic conditions in any putative ocean, which were unparalleled on Earth, and prevented carbonate precipitation on Mars. Altogether, our results show that the strength of sulphur degassing, and thus the compositions of planetary atmospheres, may have widely varied between planets of the Solar system, depending in particular upon the redox state prevailing during accretion or its modification thereafter : present day Io volcanism could ressemble what was once Mars magmatism.
DE: 0370 Volcanic effects (8409)
DE: 1011 Thermodynamics (0766, 3611, 8411)
DE: 3612 Reactions and phase equilibria (1012, 8412)
DE: 8430 Volcanic gases
SC: Volcanology, Geochemistry, Petrology [V]
MN: 2007 Fall Meeting