Chronological study of oxygen isotope composition for the solar protoplanetary disk recorded in a fluffy Type A CAI from Vigarano

摘要: Abstract Fluffy Type A Ca–Al-rich inclusions (CAIs) containing reversely zoned melilite crystals are suggested to be aggregates of direct condensates from solar nebular gas. We conducted an investigation 26 Al− Mg systematics a fluffy CAI Vigarano, named V2-01, with known oxygen isotopic distributions crystals; we also isotope measurements coexisting minerals. Two six show continuous variations in magnesium composition, δ 25 decreasing along the inferred direction crystal growth, which supports idea that they originated through condensation. Petrography suggests constituent minerals V2-01 formed following order: first spinel and fassaite enclosed by melilite, then crystals, diopside Wark–Lovering rim. The has 16 O-rich compositions (Δ 17 O ∼ −24‰) on Al−Mg evolutionary diagram plots model isochron initial value ( Al/ 27 Al) 0  = (5.6 ± 0.2) × 10 −5 . shows variable O ∼ −12‰ −17‰) showed Δ O suggesting surrounding gas, during formation changed O-poor values larger than −10‰) O ∼ −25‰). indistinguishable Al average (4.7 ± 0.3) × 10 , is clearly distinguishable fassaite, indicating younger age fassaite. rim O ∼ −23‰)  = (4.5 ± 0.4) × 10 consistent sequence petrography. period for estimated 0.18 ± 0.07 Myr difference values. These data suggest composition gas back ∼0.2 Myr Solar System formation.