HR: 1330h
AN: P12B-1070    [PDF]
TI: PGEs, Re, Mo, W and Au in Meteoritic Fe-Ni Metal and the Differentiation of Metal-rich Meteoritic Parent Bodies
AU: * Jacobsen, S B
EM: jacobsen@neodymium.harvard.edu
AF: Department of Earth and Planetary Sciences, Harvard University, 20 Oxford Street, Cambridge, MA 02138 United States
AU: Petaev, M I
EM: mpetaev@cfa.harvard.edu
AF: Department of Earth and Planetary Sciences, Harvard University, 20 Oxford Street, Cambridge, MA 02138 United States
AU: Petaev, M I
EM: mpetaev@cfa.harvard.edu
AF: Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138 United States
AB: Extinct nuclide (182Hf, 53Mn, 26Al) evidence suggests that achondrite parent planets formed and differentiated within 2-4 Ma of the origin of the Solar System. Since then many of these parent planets have been disrupted, often leaving behind only fragments of their cores in the form of iron meteorites. Thus, chemical and isotopic studies of iron meteorites can provide important information about the early differentiation of asteroidal parent bodies. Iron meteorites exhibit both old metal-silicate segregation ages (182Hf-182W extinct nuclide system) and younger crystallization ages (long-lived 187Re-190Pt-187,186Os systems). To make use of the discordant age information exhibited by different isotopic systems we have initiated a study aiming to model the trace element behavior during the early stages of planetary evolution together with the isotopic evolution of both long-lived and extinct isotope systems. We expect to establish reliable timescales of the metal-silicate fractionation and core crystallization in the parent planets of iron meteorites. For the purpose of such study we have obtained, for the first time, a consistent set of concentrations of Mo, Ru, Rh, W, Re, Os, Ir, Pt, and Au in the iron meteorites Arispe, Bennett County, Grant, Cape of Good Hope, Cape York, Carbo, Chinga, Coahuila, Duchesne, Gibeon, Henbury, Mundrabilla, Negrillos, Odessa, Sikhote-Alin, and Toluca. The measurement technique involves EPMA and LA-ICP-MS analyses of individual phases of iron meteorites, followed by calculation of bulk compositions. The comparison of our LA-ICP-MS data for a number of iron meteorites with high-precision isotope dilution and INAA data demonstrates good precision and accuracy of our technique. The narrow ranges of variations of Mo and Pd concentrations within individual groups of iron meteorites suggest that these elements can provide important insights in the evolution of parent bodies of iron meteorites. Mo concentrations can be used to estimate mass fractions of the metal-sulfide cores in the parent bodies of iron meteorites. Pd variations within a group of iron meteorites can serve as a useful indicator of S content in the core of its parent body.
DE: 1040 Isotopic composition/chemistry
DE: 1060 Planetary geochemistry (5405, 5410, 5704, 5709, 6005, 6008)
DE: 1065 Trace elements (3670)
DE: 6040 Origin and evolution
DE: 6205 Asteroids and meteoroids
SC: Planetary Sciences [P]
MN: 2003 Fall Meeting