HR: 09:15h
AN: P31A-06    [PDF]
TI: Tharsis: Consequence of Mars' Dichotomy and Layered Mantle
AU: * Wenzel, M J
EM: markw@seismo.berkeley.edu
AF: Department of Earth and Planetary Science, University of California, Berkeley, 307 McCone Hall, Berkeley, CA 94720 United States
AU: Manga, M
EM: manga@seismo.berkeley.edu
AF: Department of Earth and Planetary Science, University of California, Berkeley, 307 McCone Hall, Berkeley, CA 94720 United States
AU: Jellinek, A M
EM: markj@physics.utoronto.ca
AF: Department of Physics, University of Toronto, 60 St. George St., Toronto, ON M5S 1A7 Canada
AB: The two largest and most striking features on Mars are the crustal dichotomy, the nearly hemispheric division in topography, gravity, crustal thickness, and age, and Tharsis, a volcanic center active from the Noachian to the present. Tharsis' long-term persistence of localized volcanism is, to the best of our knowledge, unique in the solar system. Explaining the timing of Tharsis volcanism, from initiation early in martian history to recent activity, has been an enduring challenge.\\ \\ Here we present an model of the martian mantle that can explain early and persistent volcanism at Tharsis by incorporating the effects of the crustal dichotomy and a compositionally layered mantle. As the crust is expected to be enriched in heat-producing elements, this dichotomy in thickness leads to a dichotomous heat flux boundary condition on the mantle, which affects the internal dynamics. The evidence for layering includes the ability of a layered mantle to simultaneously meet a chondritic bulk composition and the moment-of-inertia factor (Elkins-Tanton et al., in revision), which can not be done with a one-layered mantle. In addition, studies of the martian meteorites suggest that the martian mantle is heterogeneous, a constraint that can be met with layering.\\ \\ We perform analog laboratory experiments with corn syrup to simulate Mars' thermal evolution. We vary the presence of a partial insulating lid, to simulate the effect of the dichotomy, and layering in the convecting fluid. We show that in the case of a layered mantle and an insulating lid, a large swell, which acts to localize upwelling plumes under the lid, forms early and endures for the scaled equivalent of billions of years.\\ \\ Linda T. Elkins-Tanton, E. M. Parmentier, and P. C. Hess, "Magma ocean fractional crystallization and cumulate overturn in terrestrial planets: implications for Mars," in revision for {\it Meteoritics and Planetary Science}.
DE: 5430 Interiors (8147)
DE: 5480 Volcanism (8450)
DE: 8121 Dynamics, convection currents and mantle plumes
SC: Planetary Sciences [P]
MN: 2003 Fall Meeting