Al‐Mg systematics of hibonite‐bearing Ca,Al‐rich inclusions from Ningqiang
Al‐Mg systematics of hibonite‐bearing Ca,Al‐rich inclusions from Ningqiang
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宁强富钙铝质包裹体的铝镁系统学
DOI：
10.1111/j.1945-5100.2011.01185.x
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发表时间：
2011
影响因子：
2.2
通讯作者：
Ying Wang
中科院分区：
文献类型：
--
作者：
W. Hsu;Y. Guan;Ying Wang
摘要-含海宝岩的富钙铝包裹体（CAIs）通常出现在CM和CH中，具有不同于其他典型CAIs的岩相学和同位素特征。尽管它们具有高度耐火的性质，但大多数含有黑云母的CAIs很少或没有26 Mg过量（26 Al的衰变产物），但确实显示出Ca和Ti同位素异常的广泛变化。一些尖晶石-黑云母球粒保留了活性26 Al的证据，推断的26 Al/27 Al接近标准值。含黑云母的CAIs中26 Al丰度的双峰分布激发了关于短寿命核素起源和太阳星云演化的几种解释。在此，我们发现宁强的含碳球粒陨石CAIs（一种未分组的碳质球粒陨石）也为26 Al的双峰分布提供了证据。两个黑碳岩集合体和两个黑碳岩-辉石球粒显示没有26 Mg过量，对应于推断的26 Al/27 Al <8 × 10−6。 两个黑云母-黄长石球粒在化学和矿物学方面彼此无法区分，但具有不同的Mg同位素组成。其中一个黑云母和黄长石显示出正的26 Mg过剩（高达25‰），与Al/Mg相关，推断26 Al/27 Al为（5.5 ± 0.6）× 10−5。 另一个含有正常的Mg同位素，推测26 Al/27 Al <3.4 × 10−6。 黑碳尖晶石碎片中的黑碳尖晶石显示出大量的26 Mg过剩（高达38‰），这与Al/Mg相关，推测26 Al/27 Al为（4.5 ± 0.8）× 10−5。 含灰云母的CAIs的形成时间延长和热蚀变似乎与宁强的岩石学和同位素观察不一致。我们的研究结果支持了在26 Al从附近的恒星源注入太阳星云之前形成无26 Al/贫含黑云母的CAIs的理论。
Abstract– Hibonite‐bearing Ca,Al‐rich inclusions (CAIs) usually occur in CM and CH chondrites and possess petrographic and isotopic characteristics distinctive from other typical CAIs. Despite their highly refractory nature, most hibonite‐bearing CAIs have little or no 26Mg excess (the decay product of 26Al), but do show wide variations of Ca and Ti isotopic anomalies. A few spinel‐hibonite spherules preserve evidence of live 26Al with an inferred 26Al/27Al close to the canonical value. The bimodal distribution of 26Al abundances in hibonite‐bearing CAIs has inspired several interpretations regarding the origin of short‐lived nuclides and the evolution of the solar nebula. Herein we show that hibonite‐bearing CAIs from Ningqiang, an ungrouped carbonaceous chondrite, also provide evidence for a bimodal distribution of 26Al. Two hibonite aggregates and two hibonite‐pyroxene spherules show no 26Mg excesses, corresponding to inferred 26Al/27Al < 8 × 10−6. Two hibonite‐melilite spherules are indistinguishable from each other in terms of chemistry and mineralogy but have different Mg isotopic compositions. Hibonite and melilite in one of them display positive 26Mg excesses (up to 25‰) that are correlated with Al/Mg with an inferred 26Al/27Al of (5.5 ± 0.6) × 10−5. The other one contains normal Mg isotopes with an inferred 26Al/27Al < 3.4 × 10−6. Hibonite in a hibonite‐spinel fragment displays large 26Mg excesses (up to 38‰) that correlate with Al/Mg, with an inferred 26Al/27Al of (4.5 ± 0.8) × 10−5. Prolonged formation duration and thermal alteration of hibonite‐bearing CAIs seem to be inconsistent with petrological and isotopic observations of Ningqiang. Our results support the theory of formation of 26Al‐free/poor hibonite‐bearing CAIs prior to the injection of 26Al into the solar nebula from a nearby stellar source.
DOI：
--
发表时间：
2005
期刊：
Astrophysical Journal 622
影响因子：
--
作者：
Krot;A.N.
通讯作者：
A.N.
DOI：
--
发表时间：
2004
期刊：
Science 305
影响因子：
--
作者：
Yurimoto H.;Kuramoto K.
通讯作者：
Kuramoto K.