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标题：Short time interval for condensation of high-temperature silicates in the solar accretion disk
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作者：Tu-Han Luu ; Edward D. Young ; Matthieu Gounelle 等
期刊名称：Proceedings of the National Academy of Sciences
印刷版ISSN：0027-8424
电子版ISSN：1091-6490
出版年度：2015
卷号：112
期号：5
页码：1298-1303
DOI：10.1073/pnas.1414025112
语种：English
出版社：The National Academy of Sciences of the United States of America
摘要：SignificanceCombining bulk and in situ Mg isotope measurements allows dating the formation of chondrule precursors relative to that of chondrules themselves. This has never been achieved before and has profound implications for the origin of chondrules, the origin of their precursors, and the evolution of the solar protoplanetary disk. There is a minimum bulk chondrule isochron, analogous in some ways to the bulk calcium-aluminum-rich inclusion isochron, which dates either the cessation of condensation of chondrule precursors or the cessation of their transport to the regions where chondrules formed. Chondritic meteorites are made of primitive components that record the first steps of formation of solids in our Solar System. Chondrules are the major component of chondrites, yet little is known about their formation mechanisms and history within the solar protoplanetary disk (SPD). We use the reconstructed concentrations of short-lived 26Al in chondrules to constrain the timing of formation of their precursors in the SPD. High-precision bulk magnesium isotopic measurements of 14 chondrules from the Allende chondrite define a 26Al isochron with 26Al/27Al = 1.2({+/-}0.2) x 10-5 for this subset of Allende chondrules. This can be considered to be the minimum bulk chondrule 26Al isochron because all chondrules analyzed so far with high precision ([~]50 chondrules from CV and ordinary chondrites) have an inferred minimum bulk initial (26Al/27Al) [≥] 1.2 x 10-5. In addition, mineral 26Al isochrons determined on the same chondrules show that their formation (i.e., fusion of their precursors by energetic events) took place from 0 Myr to [~]2 Myr after the formation of their precursors, thus showing in some cases a clear decoupling in time between the two events. The finding of a minimum bulk chondrule 26Al isochron is used to constrain the astrophysical settings for chondrule formation. Either the temperature of the condensation zone dropped below the condensation temperature of chondrule precursors at [~]1.5 My after the start of the Solar System or the transport of precursors from the condensation zone to potential storage sites stopped after 1.5 My, possibly due to a drop in the disk accretion rate.
关键词：Mg isotope analyses ; MC-SIMS ; HR-MC-ICPMS ; chondrule history ; short-lived ²⁶Al