Other
Scientific paper
Dec 2005
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2005agufm.p53a..08f&link_type=abstract
American Geophysical Union, Fall Meeting 2005, abstract #P53A-08
Other
5220 Hydrothermal Systems And Weathering On Other Planets, 5455 Origin And Evolution, 6040 Origin And Evolution, 6221 Europa, 8424 Hydrothermal Systems (0450, 1034, 3017, 3616, 4832, 8135)
Scientific paper
The recent discovery of electrolyte-enriched liquid water layer in Jupiter icy satellite, Europa, has triggered numerous investigations to assess the chemical composition and physicochemical processes occurring within Europan ocean. Europa appears to be strongly differentiated composed by a metallic core and a hydrated silicate mantle. Thus, heat fluxes could be generated in the planetary core through radioactive decay stimulating volcanic events and serving as the driving force for subseafloor hydrothermal activity. Beyond doubt, the chemical composition of the seawater and the oceanic substrate on Europa plays a key role in regulating pH and redox reactions during presumed hydrothermal alteration processes. Hydrothermal alteration of basalt and peridotite, for example, will likely yield different pH conditions, with the ultramafic-hosted hydrothermal system resulting in higher pH, significantly affecting the ratio of reduced/oxidized sulfur and the metal fluxes. Incipient alteration of basalt and peridotite will also generate reducing conditions, although the H2/H2S ratio of the coexisting fluid will be higher in the ultramafic systems. An important chemical control on Europan ocean evolution is the redox state of the sulfur originated from the oceanic crust and the SO4-enriched neutral-alkaline seawater. In general, relatively alkaline and oxidizing conditions favor the formation of SO4, while more acidic and reducing conditions yield H2S(aq) stable. Thus, hydrothermal alteration of basalt and peridotite facilitates sulfate reduction, while constraints imposed by a more oxidizing mineral assemblage (e.g. hematite-magnetite-pyrite) would render low H2(aq) conditions inhibiting formation of reduced sulfate species. Extensive hydrothermal alteration of fresh basalt, however, forming epidote and anhydrite, would preclude phase equilibria involving hematite. Consequently, initial neutral pH would be shifted towards more acidic conditions, limiting by this way any significant hydrothermal flux of sulfate back into the Europan ocean. Thermodynamic calculations at elevated P-T conditions, assuming significantly briny Mg-SO4 oceanic water, however, suggest that anhydrite and hematite can coexist, rendering extreme oxidizing and low pH conditions. Moreover, salting-out effects associated with the neutral H2(aq) and H2S(aq) aqueous species will impose serious limitations on the range of redox conditions achieved, affecting the overall mineral-fluid equilibria predicted through theoretical models.
Foustoukos D.
Seyfried William
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