HR: 08:15h
AN: P31C-02    [Abstracts]
TI: A Primitive Achondrite With Oxygen Isotopic Affinities to CV Chondrites: Implications for Differentiation and Size of the CV Parent Body
AU: * Irving, A J
EM: irving@ess.washington.edu
AF: Dept. of Earth $&$ Space Sciences, University of Washington, Seattle, WA 98195 United States
AU: Larson, T E
AF: Dept. of Earth Sciences, University of Western Ontario, London, ON N6A 5B7 Canada
AU: Longstaffe, F J
AF: Dept. of Earth Sciences, University of Western Ontario, London, ON N6A 5B7 Canada
AU: Rumble, D
AF: Geophysical Laboratory, 5251 Broad Branch Rd., N.W., Washington, DC 20015 United States
AU: Bunch, T E
AF: Dept. of Geology, Northern Arizona University, Flagstaff, AZ 86011 United States
AU: Wittke, J H
AF: Dept. of Geology, Northern Arizona University, Flagstaff, AZ 86011 United States
AU: Kuehner, S M
AF: Dept. of Earth $&$ Space Sciences, University of Washington, Seattle, WA 98195 United States
AB: NWA 3133 found in Northwest Africa (as several stones totaling $\sim$ 4 kg) has a metamorphic texture with $\sim$120$\deg$ triple grain junctions (mean grainsize = 0.28 mm); no chondrules are present. Olivine (46 vol.$%$; Fa$_{22}$, FeO/MnO = 64) and orthopyroxene (28 vol.$%$; Fs$_{18.9}$Wo$_{2.3}$, FeO/MnO = 42) are the most abundant phases, with less intermediate plagioclase (An$_{53.5}$Or$_{2.3}$), Cr-diopside (Fs$_{7.5}$Wo$_{48.3}$, Cr$_{2}$O$_{3}$ = 0.71 wt.$%$), Al-Ti-bearing chromite (Cr/(Cr+Al) = 0.73, TiO$_{2}$ = 2.6 wt.$%$), Na-Mg-bearing merrillite, troilite (1-5 wt.$%$ Ni) and Fe-Ni metal (15-20 wt.$%$ Ni). Clinopyroxene, chromite and merrillite are inhomogeneously distributed as relatively large grains. Metal is partially altered to limonite (W1-2), and minor limonite and calcite occur along grain boundaries. Oxygen isotopic compositions ($\delta$$^{17}$O, $\delta$$^{18}$O) determined in two laboratories by laser fluorination on handpicked olivine (-3.67, +0.94; -3.62, +0.89; -2.91, +1.78 per mil) and on acid-washed whole rock fragments (-2.25, +2.46; -1.75, +3.06 per mil) plot on the mixing line for Allende and other CV3 chondrites. Thus, NWA 3133 could be regarded as the first known "CV7 chondrite", and may have been formed by metamorphic recrystallization (or perhaps igneous processes) in the CV parent body. Other meteorites with oxygen and/or Cr isotopic affinities to the CV3 chondrites are the three members of the Eagle Station pallasite grouplet and the silicated irons Bocaiuva and NWA 176 (Clayton and Mayeda., 1996; Liu et al, 2001; Shukolyukov and Lugmair, 2001). Our inference from these data is that the CV parent body was an at least partially differentiated (and relatively large) object consisting of a metal+silicate core region surrounded by a presumably silicate-rich mantle and a chondrule-CAI-rich regolith, the deepest portions of which were metamorphosed and/or partially melted to form primitive achondritic lithologies.
DE: 6240 Meteorites and tektites
DE: 3660 Metamorphic petrology
DE: 3662 Meteorites
DE: 1040 Isotopic composition/chemistry
SC: Planetary Sciences [P]
MN: 2004 AGU Fall Meeting