Oxygen isotopes and high ^(26)Mg excesses in a U-depleted fine-grained Allende CAI

Abstract

CAIs are thought to be among the first solids formed in the early Solar System (ESS). As such, they are prime samples to study when (1) investigating ESS high-temperature processes, and (2) searching for evidence of short-lived radionu-clides at the time of formation of the SS. A recent systematic study of fine-grained CAIs characterized by a Group II REE pat-tern from Allende [1], found an extremely large ^(235)U excess (δ^(235)U >50 ‰ rel. to CRM-112a) in one sample: ME-3364 3.2. The discovery of this large ^(235)U excess provides definite evidence of the existence of live ^(247)Cm in the ESS, as previously suggested by [2]. In this study, we analyzed the oxygen isotope composi-tions and Al-Mg systematics of CAI ME-3364 3.2 to constrain the conditions of its formation.

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