Electron-microprobe dating of monazite: The story
Electron-microprobe dating of monazite: The story
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DOI：
10.1016/j.chemgeo.2017.11.001
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发表时间：
2017-11
期刊：
影响因子：
3.9
通讯作者：
J. Montel;Takenori Kato;M. Enami;A. Cocherie;F. Finger;Michael L. Williams;M. Jercinovic
中科院分区：
文献类型：
--
作者：
J. Montel;Takenori Kato;M. Enami;A. Cocherie;F. Finger;Michael L. Williams;M. Jercinovic
本文是独居石电子探针测年技术在90年代早期发展的见证。从名古屋、克莱蒙-费兰德、奥尔良、萨尔茨堡和阿默斯特收集了五份资料。这项技术是由名古屋的铃木教授使用旧的JXA-5A JEOL电子显微探针设计的。第一批结果于1991年发表，困难重重。铃木教授还创建了类似等时线的Pb-Th* 图来展示数据。方法的逐步改进最终使名古屋团队能够确定新生代独居石的年代。这项技术是在克莱蒙-费兰德使用Cameca Camebax微探针重新发现的。该团队证明了该方法的准确性，并提出了统计工具来提高精度和处理多模态人群。第一批结果于1993年发表。在奥尔良，法国地质调查局（BRGM）利用Cameca SX 50开发了该方法，以支持绘图项目。他们开发了一种计算年龄的新方法，并表明这种技术对确定混合岩中独居石的年龄非常有效。1996年，在萨尔茨堡，使用Jeol JX 8600获得了第一个结果。在阿尔卑斯山地区，区分Cadomian、Ordovician、Variscan和Alpine事件是非常有效的。它使该团队能够直接确定他们首次描述的独居石-褐帘石反应的日期。最后，阿默斯特小组详细研究了电子探针独居石测年的技术问题。他们表明，最好的分析程序必须至少包括：详细的化学绘图，几个干扰校正和特殊照顾的背景测量。在Cameca的帮助下，他们设计了一种用于测年的特定微探针，名为“Ultrachron”。利用这台仪器，可以在薄片上获得具有良好特征的单个颗粒的高精度年龄，开创了复杂变质岩年代学的新纪元。
This paper is a testimony of how electron microprobe dating of monazite was developed in the early days of this technique, in the 90's. Five contributions have been collected from Nagoya, Clermont-Ferrand, Orléans, Salzburg, and Amherst. The technique was designed in Nagoya by Professor Suzuki, using an old JXA-5A JEOL electron microprobe. The first results were published in 1991, with great difficulty. Professor Suzuki also created the isochron-like Pb-Th* diagram to present the data. Progressive improvement of the method finally allowed the Nagoya team to date Cenozoic monazite. The technique was re-discovered in Clermont-Ferrand using a Cameca Camebax microprobe. This team demonstrated the accuracy of the method, and proposed statistical tools to improve the precision and to handle multimodal populations. The first results were published in 1993. In Orléans, the French Geological Survey (BRGM) developed the method with a Cameca SX50 to support mapping projects. They developed a new method for calculating the age, and showed that this technique was very efficient for dating monazite in migmatites. In Salzburg, the first results were obtained in 1996, using a Jeol JX 8600. It proved to be very efficient in the Alps to distinguish Cadomian, Ordovician, Variscan and Alpine events. It allowed this team to directly date a monazite-allanite reaction they described for the first time. Finally, the Amherst team investigated in detail the technical issues of electron microprobe monazite dating. They showed that the best analytical procedures must include at least: detailed chemical mapping, several interference corrections and special care for background measurements. With the help of Cameca they designed a specific microprobe for dating, named “Ultrachron”. With this machine, high precision ages can be obtained on well characterized individual grains in thin section, giving birth to a new era in geochronology of complex metamorphic rocks.