Mathematics – Logic
Scientific paper
Dec 2001
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2001agufm.p32c0564k&link_type=abstract
American Geophysical Union, Fall Meeting 2001, abstract #P32C-0564
Mathematics
Logic
5430 Interiors (8147), 6225 Mars, 8121 Dynamics, Convection Currents And Mantle Plumes
Scientific paper
The shergottite meteorites are the most common type of the so-called SNC meteorites, which are believed to be from Mars. The shergottites are igneous rocks, many with radiometric ages of about 180 million years. Observations of very low crater density in some Mars Global Surveyor images indicate that parts of the Tharsis and Elysium volcanic provinces on Mars have been active in the last 30 million years. Together, these observations indicate that volcanism has been an important process in the recent past on Mars. Thus, upwelling mantle convection and adiabatic decompression melting likely remain important at present on Mars. I am using finite element mantle convection simulations to explore the relationship between convection and magmatism on Mars. The best existing observational constraint on deep density heterogeneities on Mars is the non-hydrostatic geoid, which is to first order axisymmetric about Tharsis. Thus, formulating the models in spherical axisymmetric geometry is a reasonable approximation. The models have a 200 km thick high viscosity near-surface layer and use radioactive heating rates and Rayleigh numbers that are appropriate for the present. Estimates for the radioactive heating rates are taken from geochemical models of Mars that are based on the observed composition of the shergottite meteorites. An important parameter being explored in these models is the fraction of total radioactivity that has fractionated into the crust of Mars. By combining temperature and velocity fields from the convection simulations with estimated melting relationships for the mantle of Mars, one can calculate a variety of quantities related to adiabatic decompression melting on Mars. (1) What is the current volumetric rate of magma production? (2) What is the spatial distribution of magma production? Is it localized near upwelling mantle plumes, or is it more widely distributed? (3) What is the typical melt fraction? What is the maximum melt fraction? (4) What depth range does melt form at? Results for 1 and 2 can be tested using regional geological mapping. Results for 3 can be tested against geochemical observations such as trace element distribution patterns in the shergottites. These comparisons between models and observations should permit new constraints on parameters such as the total radioactivity budget and the fraction of the radioactivity that is contained in the crust. >http://www.lpi.usra.edu/science/kiefer/home.html
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