@Article{Aleon:2005, author = {J. Al\'{e}on and A.N. Krot and K.D. McKeegan and G.J. MacPherson and A. Ulyanov}, title={Fine-grained, spinel-rich inclusions from the reduced {CV3} chondrite {E}fremovka : {II}. {O}xygen isotopic compositions}, journal={Meteor. Planet. Sci.}, year={2005}, volume={40}, number={}, month={Jul}, pages={1043--1058}, note={}, annote={}, keywords={}, url={http://sims.ess.ucla.edu/PDF/Aleon_et_al_MAPS_2005.pdf}, doi={}, abstract={Oxygen isotopes have been measured by ion microprobe in individual minerals (spinel, Al-Ti-diopside, melilite, and anorthite) within four relatively unaltered, fine-grained, spinel-rich Ca-Alrich inclusions (CAIs) from the reduced CV chondrite Efremovka. Spinel is uniformly $^{16}$O-rich ($\Delta$$^{17}$O $\geq$ -20$\permil$) in all four CAIs; Al-Ti-diopside is similarly $^{16}$O-rich in all but one CAI, where it has smaller $^{16}$O excesses (-15$\permil$ $\geq$ $\Delta$$^{17}$O $\geq$ -10$\permil$). Anorthite and melilite vary widely in composition from $^{16}$O-rich to $^{16}$O-poor (-22$\permil$ $\geq$ $\Delta$$^{17}$O $\geq$ -5$\permil$). Two of the CAIs are known to have group II volatility-fractionated rare-earth-element patterns, which is typical of this variety of CAI and which suggests formation by condensation. The association of such trace element patterns with $^{16}$O-enrichment in these CAIs suggests that they formed by gas-solid condensation from an $^{16}$O-rich gas. They subsequently experienced thermal processing in an $^{16}$O-poor reservoir, resulting in partial oxygen isotope exchange. Within each inclusion, oxygen isotope variations from mineral to mineral are consistent with solid-state oxygen self-diffusion at the grain-to-grain scale, but such a model is not consistent with isotopic variations at a larger scale in two of the CAIs. The spatial association of $^{16}$O depletions with both elevated Fe contents in spinel and the presence of nepheline suggests that late-stage iron-alkali metasomatism played some role in modifying the isotopic patterns in some CAIs. One of the CAIs is a compound object consisting of a coarse-grained, melilite-rich (type A) lithology joined to a fine-grained, spinel-rich one. Melilite and anorthite in the fine-grained portion are mainly $^{16}$O-rich, whereas melilite in the type A portion ranges from $^{16}$O-rich to $^{16}$O-poor, suggesting that oxygen isotope exchange predated the joining together of the two parts and that both $^{16}$O-rich and $^{16}$O-poor gaseous reservoirs existed simultaneously in the early solar nebula.} } %%%%% 2006 Publications %%%%%