HR: 0800h
AN: P31A-0961    [Abstracts]
TI: Stresses Generated in Cooling Viscoelastic ice Shells: Application to Europa
AU: * Nimmo, F
EM: nimmo@ess.ucla.edu
AF: Dept. Earth and Space Sciences, UCLA, 595 Charles Young Drive E, Los Angeles, CA 90095-1567 United States
AB: A cooling and thickening viscoelastic ice shell overlying an ocean develops stresses due to two effects: thermal contraction of the ice due to cooling; and the expansion of the shell due to the ice-water volume change. The former effect generates near-surface compression and deeper extension; the second effect generates extension only. In both cases, stresses generally decrease with depth due to viscous creep. The resulting combined stresses are extensional except at shallow ($<$1~km) depths in thin ice shells. These extensional stresses exceed 10~MPa for shells thicker than 20~km, and thus dominate all other likely sources of stress as long as shell cooling occurs. The dominantly extensional nature of the stresses may help to explain the puzzling lack of compression observed on Europa, Ganymede and other large icy satellites. In particular, the proposed mechanism suggests that Europa's extensional features are due to a thickening ice shell, in agreement with observed stratigraphic relationships and impact crater characteristics.
DE: 8160 Rheology--general
DE: 5430 Interiors (8147)
DE: 5475 Tectonics (8149)
DE: 6218 Jovian satellites
SC: Planetary Sciences [P]
MN: 2004 AGU Fall Meeting