Heterogeneous distribution of 26Al at the birth of the Solar System: Evidence from corundum-bearing refractory inclusions in carbonaceous chondrites

摘要: Abstract We report on the mineralogy, petrology, and in situ oxygen- magnesium-isotope measurements using secondary ion mass spectrometry of 10 corundum-bearing calcium–aluminum-rich inclusions (CAIs) from Adelaide (ungrouped), Murray Murchison (CM) carbonaceous chondrites. also measured oxygen-isotope compositions several isolated corundum grains matrices Murchison. Most objects studied are uniformly 16O-rich [Δ17O values range −17‰ to −28‰ (2σ = ±2.5‰) (Δ17Oavr = −23 ± 5‰)], suggesting that they formed a gas approximately solar composition largely avoided subsequent thermal processing an 16O-poor gaseous reservoir. There is large spread initial 26Al/27Al ratio [(26Al/27Al)0] CAIs. Two CAIs show no resolvable excess radiogenic 26Mg (δ26Mg∗): inferred (26Al/27Al)0 (0.6 ± 2.0) × 10−6 (−0.9 ± 1.2) × 10−6, respectively. Slopes model 26Al–26Mg isochrons five (4.4 ± 0.2) × 10−5, (3.3 ± 0.3) × 10−5, (4.1 ± 0.3) × 10−5, (3.9 ± 0.4) × 10−5, (4.0 ± 2.0) × 10−6, These lower than canonical (5.23 ± 0.13) × 10−5 whole-rock CV CAIs, but similar (4.1 ± 0.2) × 10−5 CAI F5 Murray. Five other previously Acfer 094 (ungrouped) CM chondrites showed δ26Mg∗. conclude as well acid-resistant residues unequilibrated ordinary chondrites, recorded heterogeneous distribution 26Al Solar System during epoch formation. The 26Al-rich 26Al-poor represent different generations refractory this epoch. As result, its duration cannot be systematics Oxygen-isotope protoplanetary disk was probably time reflecting either differences oxygen isotopic solid reservoirs early or rapid evolution these with time. suggest injected into protosolar molecular cloud core, possibly by wind neighboring massive star low-mass asymptotic giant branch star, prior formation grains, subsequently homogenized through radial mixing.