Precise U-Pb and Pb-Pb dating of Phanerozoic baddeleyite by SIMS with oxygen flooding technique
Precise U-Pb and Pb-Pb dating of Phanerozoic baddeleyite by SIMS with oxygen flooding technique
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SIMS氧驱法对显生界斜锆石进行U-Pb和Pb-Pb精密定年
DOI：
10.1039/b923444f
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发表时间：
2010-01-01
影响因子：
3.4
通讯作者：
Zhu, Wei-Guang
中科院分区：
文献类型：
--
作者：
Li, Qiu-Li;Li, Xian-Hua;Zhu, Wei-Guang
斜锆石是硅不饱和火成岩测年的重要含铀矿物之一。斜锆石的年龄测定要求在小体积内使用高分辨率二次离子质谱（西姆斯）进行分析，因为它的粒度很小，以及潜在的蚀变域或微包裹体。然而，精确的西姆斯U-Pb测年一直阻碍斜锆石由于晶体取向的影响，偏见的Pb/U比测量斜锆石。本文利用Cameca 1280型多接收器IMS氧驱技术对古生代斜锆石进行了U-Pb和Pb-Pb测量。结果表明，氧驱不仅使斜锆石的二次Pb+离子产率提高了7倍，而且使斜锆石U/Pb取向效应降低到约2%（RSD = 1）。因此，西姆斯Pb-Pb和/或U-Pb测量可以精确测定新生代斜锆石的年龄，其精度为1-3%（2 RSE）。
Baddeleyite has long been recognized as one of the most important U-bearing minerals for dating silica undersaturated igneous rocks. Age determination of baddeleyite calls for analysis within small volumes using high-resolution secondary ion mass spectrometry (SIMS) because of its minuscule grain size as well as potential altered domains or micro-inclusions. However, precise SIMS U-Pb dating has been hampered for baddeleyite owing to crystal orientation effects that bias Pb/U ratio measured in baddeleyite. In this study we carried out a series of tests of U-Pb and Pb-Pb measurements on Phanerozoic baddeleyite using a multi-collector Cameca 1280 IMS with oxygen flooding technique. Our results demonstrate that the oxygen flooding can not only enhance secondary Pb+ ion yield by a fact of 7 for baddeleyite, but also depress the baddeleyite U/Pb orientation effect down to similar to 2% (1 RSD). Therefore, Phanerozoic (as young as Cenozoic) baddeleyite can be precisely dated by SIMS Pb-Pb and/or U-Pb measurements with precision of 1-3% (2 RSE).