In-situ SIMS U-Pb dating of phanerozoic apatite with low U and high common Pb
In-situ SIMS U-Pb dating of phanerozoic apatite with low U and high common Pb
复制标题
低U高共Pb显生宙磷灰石原位SIMS U-Pb定年
DOI：
10.1016/j.gr.2011.07.008
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发表时间：
2012-05-01
影响因子：
6.1
通讯作者：
Zhang, Chuan-Lin
中科院分区：
文献类型：
--
作者：
Li, Qiu-Li;Li, Xian-Hua;Zhang, Chuan-Lin
磷灰石是各种火成岩、变质岩和沉积岩中常见的副矿物。它具有很强的潜力，为地质年代学和岩石成因提供重要信息。然而，由于磷灰石，特别是年轻样品的U丰度较低，且放射性成因较少，因此很难对其进行精确的U- th -Pb定年，这对准确的普通Pb校正提出了重大挑战。另一个问题是缺乏合适的磷灰石作为原位分析的标准。本文提出了低U高铅磷灰石的SIMS原位U- pb分析的分析和数据简化方案。以从加拿大草原湖杂岩中分离出的NW-1磷灰石为U-Pb年龄标准，从科拉半岛的科夫多碳酸岩中分离出的磷灰石，其U-Pb年龄为低U（大部分接近2.5 ppm）和高普通Pb(20-80%)，加权平均Pb- Pb年龄分别为375 +/- 13 Ma （KV-8和KV-18）和377 +/- 11 Ma （KV-A）。来自中国西北库鲁克塔格超镁质岩体的磷灰石含低U（接近2.3 ppm）和高普通Pb (bbb70 %)，其Pb-207校正U-Pb年龄为805 +/- 21 Ma。新生代杜兰戈磷灰石年龄为31 +/- 2 Ma。所有这些新的磷灰石U-Pb年龄与独立已知的年龄约束在2-4%之间难以区分。我们的研究结果表明，通过适当的标准和仔细选择常见的Pb组成，SIMS可以准确准确地测量低U（50%）磷灰石的U-Pb年龄。(C) 2011年国际冈瓦纳研究协会。Elsevier B.V.版权所有。
Apatite is a common accessory mineral in various igneous, metamorphic and sedimentary rocks. It has strong potential to provide important information for geochronology and petrogenesis. However, precise U-Th-Pb dating of apatite, especially young samples, is difficult due to low abundances of U and less radiogenic Pb, posing significant challenges for accurate common Pb correction. An additional issue is the lack of suitable apatite to serve as a standard for in-situ analyses. Here we present both analytical and data reduction protocols for SIMS in-situ U-Pb analyses on apatite with low U and high common lead. With NW-1 apatite as the U-Pb age standard, which was separated from similar to 1160 Ma carbonatite in the Prairie Lake complex in Canada, apatites from the Kovdor carbonatite in the Kola peninsula which contains low U (mostly similar to 2.5 ppm) and high common Pb (20-80%) yielded weighted average Pb-207-corrected U-Pb ages of 375 +/- 13 Ma (KV-8 and KV-18) and 377 +/- 11 Ma (KV-A), respectively. Apatites from the Quruqtagh ultramafic intrusion in NW China containing low U (similar to 2.3 ppm) and high common Pb (>70%) yield Pb-207-corrected U-Pb age of 805 +/- 21 Ma. The Cenozoic Durango apatite was dated at 31 +/- 2 Ma. All these new apatite U-Pb ages are indistinguishable from independently known age constraints to within 2-4%. Our results demonstrate that a U-Pb age can be accurately and precisely measured for apatite with low U (50%) by SIMS with a suitable standard and a careful choice of common Pb composition. (C) 2011 International Association for Gondwana Research. Published by Elsevier B.V. All rights reserved.