Physics
Scientific paper
Dec 2002
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2002agufm.p12c..11m&link_type=abstract
American Geophysical Union, Fall Meeting 2002, abstract #P12C-11
Physics
5418 Heat Flow, 5430 Interiors (8147), 6218 Jovian Satellites
Scientific paper
Some of the most visually distinctive features on Europa's surface are the ~ 10 km-diameter roughly circular lenticulae. Many are domes, showing positive elevations of up to ~~100~m, and sometimes displaying surrounding moats. Most explanations for lenticulae formation have suggested some kind of diapiric or convective activity though icy volcanism and melt-through of the icy crust have also been considered. We investigate a specific model of dome formation by diapirism. In strongly temperature-dependent convection, a stagnant lid forms at the surface with approximately isoviscous convection occurring beneath this lid. The hot bottom boundary layer creates discrete buoyant regions which are often termed ``thermals'' or ``diapir plumes''. These diapirs will spread laterally as the stagnant lid is approached. The density difference between the diapir and the surrounding ice gives rise to the surface deformation, which will also be affected by the stagnant lid thickness. By using observations of dome diameter we can constrain the thickness of the top (stagnant) and bottom thermal boundary layers, and hence infer the characteristics of the convecting system. Most of the inferences are not sensitive to the thickness of the ice layer. We use the observed lower limit on dome diameter of 4~km to deduce that the conductive (stagnant) lid thickness must be <=~5~km. Such a lid thickness implies a minimum surface heat flux of 90~mW/m2, compatible with recent estimates of tidal heating. We also use the mean observed dome diameter to infer a lower thermal boundary layer thickness of ~~1~km. We find that the ice is probably deforming in the diffusion creep regime with a grain size in the range 0.02-0.06~mm. The fraction of internal heating is >0.5, the ice viscosity 1012-1013~Pa~s, and the crustal solidification rate < 5km/Ma.
Manga Michael
Nimmo Francis
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