Well-resolved variations in the formation ages for Ca-Al-rich inclusions in the early Solar System

Recent whole-rock magnesium-isotopic data for calcium-aluminum-rich inclusions (CAIs) in chondrite meteorites indicate that the primary nebular fractionation of aluminum from magnesium, probably by condensation, occurred within <20,000 years at 4.567 Ga. However, high-precision multicollector ion microprobe data for diverse CAIs from Vigarano (CV3) yield internal isochrons with a clearly resolved spread in initial Al-26/Al-27, meaning that CAIs formed and were reprocessed over a much longer time span. Primitive (unmelted) CAIs have a consistent value of 52 +/- 0.1 x 10(-5), melted CAIs range from 5.17 x 10(-5) to 4.24 x 10(-5), and one single object with a complex multistage history has an internal range of Al-26/Al-27 = (4.77 - 2.77) x 10(-5). The entire range corresponds to an age span of similar to 0.7 Ma. Thus not all CAIs formed at time zero, and only the most primitive CAIs should be used as benchmarks for earliest Solar System chronology. Published by Elsevier B.V.