HR: 09:00h
AN: P31A-05    [Abstracts]
TI: Geochemistry of Asteroid 4 Vesta: HED Meteorites as Constraints for Interpreting Gamma- Ray and Neutron Spectra from the Dawn Mission
AU: * McSween, H Y
EM: mcsween@utk.edu
AF: Department of Earth and Planetary Sciences, University of Tennessee, Knoxville, TN 37996-1410, United States
AU: Usui, T
EM: tusui@utk.edu
AF: Department of Earth and Planetary Sciences, University of Tennessee, Knoxville, TN 37996-1410, United States
AB: Rotational spectra of Vesta have revealed compositionally distinct units that are smaller than the footprint of the GRaND instrument on the Dawn orbiting spacecraft. Geochemical analyses by GRaND will thus represent lithologic mixtures. HED meteorites, thought to have been derived from Vesta, can be used to quantify the admixed components. Using selected meteorites representing basaltic eucrite, cumulate eucrite, and diogenite as endmembers, we have modeled the chemical compositions of other HED meteorites. Element ratios are more accurately determined by this method than are absolute element abundances. A mixing model utilizing molar (Mg+Fe)/Si versus Al/Si ratios accurately calculates all major and minor element abundances. Surface analyses of Vesta can thus be deconvolved into the relative proportions of these HED lithologies. In addition, the model calculates the abundances of elements not analyzed by GRaND, such as Na, Mn, and Cr. The full set of elements enables the calculation of normative mineralogy, which can be compared with minerals identified by Dawn's VIR spectrometer. Another model, substituting Ca/Si for Al/Si, allows the direct estimation of olivine proportions in olivine-bearing diogenites, and presumably within a large 460 km-diameter crater that exposures the mantle or lower crust on Vesta.
DE: 5410 Composition (1060, 3672)
DE: 6063 Volcanism (5480, 8450)
DE: 6205 Asteroids
DE: 6240 Meteorites and tektites (1028, 3662)
DE: 6297 Instruments and techniques
SC: Planetary Sciences [P]
MN: 2007 Joint Assembly