Pb-Pb ages of feldspathic clasts in two Apollo 14 breccia samples
Pb-Pb ages of feldspathic clasts in two Apollo 14 breccia samples
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DOI：
10.1016/j.gca.2017.08.024
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发表时间：
2017-11
影响因子：
5
通讯作者：
A. Nemchin;H. Jeon;J. Bellucci;N. Timms;J. Snape;M. Kilburn;M. Whitehouse
中科院分区：
文献类型：
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作者：
A. Nemchin;H. Jeon;J. Bellucci;N. Timms;J. Snape;M. Kilburn;M. Whitehouse
用二次离子质谱仪(SIMS)测定了阿波罗14号角砾岩14303和14083中3个富钾长石碎屑的PbPb等时线年龄(约3.92nGa)。这些年龄被解释为代表了碎屑中U-Pb系统的重新设置，这是在海盆撞击期间角砾作用的结果。其中一个碎屑含有锆石颗粒，记录了该碎屑所代表的岩石的明显较老的结晶年龄(约4.33-4.35Ga)。碎屑的初始铅成分测定，结合之前从几个阿波罗14号角砾岩样品中测得的钾长石颗粒的铅同位素组成，限制了阿波罗14号着陆点约3.9GaFra毛罗组的初始铅成分范围。这些碎屑所代表的岩石或这些岩石的来源在相当长的一段时间内以高的238U/204Pb(μ值)演化，尽管这里所研究的至少两个碎屑所代表的岩石的精确结晶年龄是未知的。
Pb-Pb isochron ages of ca. 3.92 Ga for three K-feldspar-rich clasts from Apollo 14 breccias 14303 and 14083 were determined using Secondary Ion Mass Spectrometry (SIMS). These ages are interpreted to represent the resetting of the U-Pb system in the clasts as a result of brecciation during the Imbrium impact. One of the clasts contains zircon grains that record a significantly older crystallization age (ca. 4.33–4.35 Ga) for the rock represented by that clast. Initial Pb compositions determined for the clasts, combined with the previously measured Pb isotopic compositions of K-feldspar grains from several Apollo 14 breccia samples, constrain a range of initial Pb compositions in the ca. 3.9 Ga Fra Mauro formation at the Apollo 14 landing site. This range in initial Pb compositions indicates that the rocks represented by these clasts, or the sources of those rocks, evolved with a high238U/204Pb (μ-value) for substantial periods of time, although the precise crystallization ages of the rocks represented by at least two of the clasts investigated here are unknown.