HR: 14:40h
AN: P53A-05 INVITED     [Abstracts]
TI: Geophysical Limits to Europan Hydrothermal History
AU: * McKinnon, W B
EM: mckinnon@wustl.edu
AF: Dept. Earth and Planetary Sci. and McDonnell Center for Space Sci., Washington University, St. Louis, MO 63130 United States
AB: As Europa accreted, the heat released would have melted accreted ice and led to the formation of a primordial ocean. Following accretion, the Europan primordial ocean would have interacted hydrothermally with the subjacent rock "core." The hydrothermal circulation would have been driven by the release of radiogenic and tidal heat and by the heat released by the serpentinization of unaltered olivine and pyroxene. The depth of this circulation is not known. Fracture-assisted hydrothermal circulation at terrestrial mid-ocean ridges extends to at least 10 km. Assuming a similar pressure scale for Europan hydrothermal systems, 300 MPa is reached at (~100 km total depth for a "thin" (~45-km-deep) ocean overlying an oxidized and hydrated but undifferentiated solar composition interior (McKinnon and Zolensky, Astrobiology 3, 879-897). The ability of hydrothermal systems to penetrate thoroughly altered "Europa rock" at depth is, however, a critical limiting factor. I expect that porosity would have been largely eliminated by precipitation, mineral bulking, and pressure-induced deformation during initial postaccretion alteration (e.g., serpentinization). The intrinsic permeability of serpentine itself is quite poor, and hydrothermal circulation in a massive, nonporous, serpentinitic Europan mantle is essentially impossible. Hydrothermal interaction more similar to that at terrestrial mid-ocean ridges, if it is to occur, would be delayed until after metallic core formation (>1 Gyr), which plausibly would have led to overturn and final dewatering of the rock mantle. In this case 300 MPa is reached ~20-25 km beneath a thick ocean.
DE: 5220 Hydrothermal systems and weathering on other planets
DE: 5430 Interiors (8147)
SC: Planetary Sciences [P]
MN: Fall Meeting 2005