TRACE-ELEMENT ABUNDANCES AND MAGNESIUM, CALCIUM, AND TITANIUM ISOTOPIC COMPOSITIONS OF GROSSITE-CONTAINING INCLUSIONS FROM THE CARBONACEOUSCHONDRITE ACFER-182

The carbonaceous chondrite Acfer 182 contains Ca, Al-rich inclusions(C AIs) that differ from most CAIs in other meteorites. Many of them cont ain grossite (CaAl4O7), whose modal abundance exceeds 30 vol % in most of these CAIs (''grossite-rich inclusions''). Similar inclusions have been found only in the CH chondrite ALH85085 and the CR chondrite Acf er 059-EI Djouf 001. Ion microprobe analyses of trace elements were ma de on nineteen CAIs from Acfer 182 and two CAIs from Acfer 059-El Djou f 001, of Al-Mg isotopes on eighteen Acfer 182 and the two Acfer 059-E l Djouf 001 inclusions, and of calcium isotopes on ten Acfer 182 inclu sions (on six of them also of titanium isotopes) and one Acfer 059-El Djouf 001 inclusion. Trace element and isotopic signatures of grossite -containing inclusions from Acfer 182 resemble those of some inclusion s from ALH85085. Volatility-fractionated trace element abundance patte rns, ranging from ultrarefractory-depleted (similar to Group II patter n) to volatile-enhanced, are predominant (17 CAIs, including both incl usions from Acfer 059-El Djouf 001). Two inclusions have ultrarefracto ry patterns, one has a Group III pattern, and one inclusion has a Grou p III-related pattern similar to patterns found in HAL-type inclusions . Only one CAI from Acfer 182, but both inclusions from Acfer 059-El D jouf 001, have nonlinear excesses of Mg-26 corresponding to the initia l Al-26/Al-27 ratio of similar to 5 x 10(-5). None of the twenty inclu sions has a significant intrinsic isotopic mass fractionation of Mg. T itanium is normal in all analyzed CAIs and only small Ca-48 excesses ( 4.3 and 3.8 parts per thousand) are present in two inclusions. Isotope s of both Ca and Ti show no significant intrinsic mass fracrionations. Grossite-containing inclusions from Acfer 182 occur in different petr ographic contexts. In many cases petrographic characteristics are corr elated with trace element abundances. Almost all inclusions studied in this work have a condensation history but no evidence for extensive e vaporation processes is present. Many of the CAIs must have formed by direct gas-solid condensation, while some inclusions with clearly iden tifiable igneous textures formed from a refractory melt. Grossite, who se formation was the subject of controversy in the past, probably cond ensed from a reservoir with a higher-than-chondritic Ca/Al-ratio and d epleted in the highly refractory trace elements, os crystallized from a Ca,Al-rich melt. The two ultrarefractory inclusions from Acfer 182 h ave extremely high refractory trace element abundances(sometimes excee ding 10(5) x CI). The lack of isotopic fractionation indicates a forma tion at very high temperatures by condensation rather than evaporation . The lack of Mg-26 excesses in almost all inclusions from Acfer 182 i s best explained by heterogeneous distribution of Al-26 in the primiti ve solar nebula. Grossiterich inclusions having volatility-fractionate d ultrarefractory-depleted trace element abundance patterns and lackin g Mg-26 excesses could be the complement of platy hibonites (PLACs) fr om Murchison with Group III or ultrarefractory patterns and likewise n o Mg-26 excesses.