The correlation of chondrule texture and magnesium isotope abundance in Allende meteorite

The Mg isotope abundance of the individual chondrules in the Allende meteorite was measured by ion microprobe mass analysis. The amounts of ^Mg excess with respect to the terrestrial fractionation line were obtained for each chondrule. Barred olivine and glassy chondrules tend to have relatively large ^Mg excess, whereas porphyritic and radial pyroxene chondrules have relatively small ^Mg excess. The following three factors were taken into consideration in connection with the formation process of these chondrules in the Allende meteorite; (1) the temperature conditions at the formation of the chondrules, (2) the relative abundance of each chondrule type, (3) the amount of ^Mg excess in each chondrule type. It is shown that chondrules formed at high temperature or by rapid cooling have relatively large ^Mg excess and their relative abundance is small, whereas chondrules formed at low temperature or by slow cooling tend to have small ^Mg excess and their relative abundance is large. A model of chondrule formation process in the early solar nebula is proposed to explain the relations between factors (1)-(3)