HR: 0800h
AN: P51B-0925    [Abstracts]
TI: Mantle Convection and the Uplift of Tharsis, Mars: The Importance of Time-Dependent Loading
AU: * Kiefer, W S
EM: kiefer@lpi.usra.edu
AF: Lunar and Planetary Institute, 3600 Bay Area Blvd., Houston, TX 77058 United States
AB: The Tharsis province on Mars is 5000 km across and up to 10 km high. The mechanisms responsible for the uplift of Tharsis remain contentious. Volcanic activity has occurred in Tharsis for most of martian history, including in the last 200 million years as required by both the igneous martian meteorites and by the impact cratering record. The occurrence of pressure-release melting requires that some form of convective upwelling has existed under Tharsis throughout martian history. This upwelling must also contribute to the topographic uplift and geoid anomaly at Tharsis. On the other hand, some investigators have concluded that a thick elastic lithosphere on Mars resists present-day convective uplift and thus limits the contribution of mantle convection to just 15-25% of the observed long-wavelength geoid and topography, with the remainder due to flexurally supported volcanic loads. Because convective upwelling under Tharsis has been important for much of martian history and because the elastic lithosphere has thickened over time, one cannot simply calculate convective topographic uplift by applying all of the present-day convective load against the present-day elastic lithosphere. Rather, the final amplitude of the convective uplift depends on the time history of the loading. Each increment of convective load must be applied against the lithosphere that exists at that point in time; the total topographic uplift can therefore be written as an integral function of convective load over time. The portion of the Tharsis convective load that existed early in martian history was applied against a thin elastic lithosphere with little ability to resist convective uplift. As Mars cooled, later incremental changes in the convective load were applied to progressively thicker lithospheres and thus were less able to produce convective uplift. Because the details of the convective loading history of Mars are not known, we can not hope to precisely calculate the present-day convective uplift at Tharsis. However, on-going analysis of several plausible loading histories should at least permit improved bounds to be set on the role convective uplift plays in present-day Tharsis.
UR: http://www.lpi.usra.edu/science/kiefer/home.html
DE: 5475 Tectonics (8149)
DE: 6225 Mars
DE: 8121 Dynamics: convection currents, and mantle plumes
SC: Planetary Sciences [P]
MN: Fall Meeting 2005