The formation of chondrules at high gas pressures in the solar nebula

High-precision magnesium isotope measurements of whole chondrules from the Allende carbonaceous chondrite meteorite show that some aluminum-rich Allen de chondrules formed at or near the time of formation of calcium-aluminum-r ich intrusions and that some others formed later and incorporated precursor s previously enriched in magnesium-26. Chondrule magnesium-25/ magnesium-24 correlates with [magnesium]/[aluminum] and size, the aluminum-rich, smalle r chondrules being the most enriched in the heavy isotopes of magnesium. Th ese relations imply that high gas pressures prevailed during chondrule form ation in the solar nebula.