Magnesium isotopic fractionations in barred olivine chondrules from the Allende meteorite

he Mg-isotopic compositions in five barred olivine (BO) chondrules, one coa rse-grained rim of a BO chondrule, a relic spinel in a BO chondrule, one sk eletal olivine chondrule similar to BO chondrules in mineralogy and composi tion, and two non-BO chondrules from the Allende meteorite have been measur ed by thermal ionization mass spectrometry. The Mg isotopes are not fractio nated and are within terrestrial standard values (+/-2.00 parts per thousan d per amu) in seven of the eight analyzed ferromagnesian chondrules. A clum p of relic spinel grain and its host BO chondrule R-11 give well-resolvable Mg fractionations that show an enrichment of the heavier isotopes, up to 2.5 parts per thousand per amu. The Mg-isotopic compositions of coarse-grai ned rim are identical to those of the host chondrule with BO texture. The r esults imply that ferromagnesian and refractory precursor components of the Allende chondrule may have been formed from isotopically heterogeneous res ervoirs. In the nebula region where Allende chondrules formed, recycling of chondrules and multiple high-temperature heating did not significantly alt er the chemical and isotopic memory of earlier generations.