Ion microprobe U-Pb dating and REE analyses of phosphates in H4-chondrite, Yamato-74371
Ion microprobe U-Pb dating and REE analyses of phosphates in H4-chondrite, Yamato-74371
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DOI：
10.1029/2001gl013945
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发表时间：
2002-05-15
影响因子：
5.2
通讯作者：
Sano, Y
中科院分区：
文献类型：
--
作者：
Terada, K;Sano, Y
[1] 使用离子微探针测量 H4 球粒陨石 Y-74371 的单个磷酸盐颗粒中的 U 和 Pb 同位素以及稀土元素 (REE)。对白磷矿（merrillite）的九次分析和对磷灰石的五次分析表明总 Pb/U 等时线年龄为 4533 +/- 40 Ma (2 sigma)，这与之前使用热电离质谱仪 (TIMS) 的结果一致。然而，观察到的磷灰石年龄为 4525 +/- 30 Ma (2 sigma)，比之前的工作要年轻。另一方面，由于存在很大的不确定性，没有观察到白磷灰石年龄 4601 +/- 94 Ma (2 sigma) 与磷灰石年龄之间的时间差异。归一化为 CI 球粒陨石的辉锁辉石的 REE 丰度模式的特点是几乎持续富集 200-800 倍 CI 丰度，以及显着的负 Eu 异常。磷灰石的稀土元素丰度低于白磷灰石颗粒，并且不同颗粒之间的稀土元素丰度存在较大差异。证实了Eu异常（Eu/Eu*）与REE总浓度之间的显着相关性，但没有观察到Eu异常与单个颗粒形成年龄的显着相关性。
[1] U and Pb isotopes and rare earth elements (REEs) in individual phosphate grains from H4-chondrites, Y-74371 were measured by using an ion microprobe. Nine analyses of whitlockite (merrillite) and five analyses of apatites indicate a total Pb/U isochron age of 4533 +/- 40 Ma (2 sigma), which are consistent with the results from previous using Thermal ionization mass spectrometer (TIMS). The observed apatites age of 4525 +/- 30 Ma (2 sigma), however, is younger than those of previous works. On the other hand, the time difference between the whitlockite age of 4601 +/- 94 Ma (2 sigma) and those of apatites are not observed, because of the large uncertainties. The REE abundance patterns of the whitlockites normalized to CI chondrite are characterized by an almost constant enrichment of 200-800 times CI abundance, and a striking negative Eu anomaly. The REE abundances of the apatites are lower than those of whitlockite grains, and vary appreciably among different grains. The remarkable correlation between the Eu anomaly (Eu/Eu*) and total concentration of REE is confirmed, but significant correlation with Eu anomaly and formation age of individual grains are not observed.