Mathematics – Logic
Scientific paper
Dec 2011
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2011agufm.p41f..09p&link_type=abstract
American Geophysical Union, Fall Meeting 2011, abstract #P41F-09
Mathematics
Logic
[5400] Planetary Sciences: Solid Surface Planets, [5422] Planetary Sciences: Solid Surface Planets / Ices
Scientific paper
Europa, a satellite of Jupiter, is one of the most intriguing worlds in the solar system. Its dearth of impact craters and plethora of surface morphologies point to a dynamic evolution of its icy shell in geologically recent times. Double ridges are a common landform on Europa and appear to have formed over a significant portion of the satellite's observed geologic history. These features can run remarkably uniformly for more than 1000 km across the surface, a challenge for any model for their formation. A clue to the formation of ridges may lie in evidence for flexure of the lithosphere in response to a load imposed by the ridge itself. Several groups have interpreted the presence of marginal troughs and subparallel flanking fractures associated with ridges as characteristic of flexure. When this flexure is modeled, a simple elastic lithosphere has typically been assumed; however, the generally thin lithospheres suggested by these models require very high heat flows that are inconsistent with Europa's expected thermal budget (of order 1 W m-2 vs. of order 10 mW m-2). Each of the proposed models, however, possesses a thermal anomaly that may facilitate the flexure of Europa's lithosphere. Here, we simulate this flexure in the presence of these anomalies, as a means to evaluate the different models of ridge formation. These models can be lumped into 4 broad classes. A first predicts regional compression near the ridge, which is not consistent with the presence of the flanking fractures. A second class possesses a central conduit where high temperatures are maintained along a vertical crack through the ice shell beneath the central axis of the ridge. A third presupposes that the ridge marks a cryovolcanic system, which in addition to a central conduit thermal anomaly also possesses a cryovolcanic sill extending away from the ridge at the depth of neutral buoyancy of water in ice (~ 1 km deep). A last class appeals to shear heating beneath the forming ridge. We simulate each of these last 3 classes using a thermomechanical finite element approach with an elastoviscoplastic rheology. While the uniformity of double ridges over long distances and the relatively short timescales for freezing of a sill remain issues, our results indicate that only the cryovolcanic sill model is consistent with the observed flexure.
Dombard Andrew J.
Lederer A. P.
Patterson Wesley G.
Prockter Louise M.
Schenk Paul
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