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首页> 外文期刊>Contributions to Mineralogy and Petrology >Micro-drilling ID-TIMS U-Pb dating of single monazites: A new method to unravel complex poly-metamorphic evolutions. Application to the UHT granulites of Andriamena (North-Central Madagascar).
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Micro-drilling ID-TIMS U-Pb dating of single monazites: A new method to unravel complex poly-metamorphic evolutions. Application to the UHT granulites of Andriamena (North-Central Madagascar).

机译：独居石的微钻ID-TIMS U-Pb定年：揭示复杂多变质演化的新方法。应用于Andriamena（马达加斯加中北部）的UHT颗粒。

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摘要

In terranes subject to complex metamorphic evolution, zircon and monazite U-Pb system can record successive growth and/or resetting episodes. Conventional isotope dilution-thermal ionisation mass spectrometry (ID-TIMS) dating of fractions or single grains from conventionally separated zircon and monazite populations may produce inaccurate ages. A new technique combining textural analysis and ID-TIMS dating on single monazite crystals is proposed. This method is applied directly on thin sections with three successive steps comprising (1) a characterisation of textural relationships using electron microprobe analyses and images, (2) extraction by micro-drilling of selected monazites and (3) U-Pb dating of each extracted grain by ID-TIMS. The potential for this “in situ” dating technique are tested on Ultra High Temperature (UHT) granulites from North-Central Madagascar. Four distinct events on a single thin section were distinguished. The UHT metamorphism was dated at 2.5 Ga, while two retrogression events were dated at 790 and 500 Ma. Finally, a single crystal shielded in quartz seems to preserve a pre-metamorphic age around 2.7 Ga.
机译：在经历复杂变质演化的地层中，锆石和独居石U-Pb系统可以记录连续的生长和/或重置事件。常规同位素稀释-热电离质谱法（ID-TIMS）对来自常规分离的锆石和独居石种群的馏分或单颗粒进行测年可能会产生不准确的年龄。提出了一种结合结构分析和ID-TIMS定年独居石晶体的新技术。该方法通过三个连续步骤直接应用于薄截面，包括（1）使用电子微探针分析和图像表征纹理关系，（2）通过微钻孔选择的独居石进行萃取以及（3）每次萃取的U-Pb测年谷物由ID-TIMS提供。在马达加斯加中北部的超高温（UHT）花岗石上测试了这种“原位”测年技术的潜力。区分了单个薄片上的四个不同事件。 UHT的变质期为2.5 Ga，两次倒退事件的日期为790和500 Ma。最后，用石英屏蔽的单晶似乎保留了约2.7 Ga的变质前年龄。

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