Laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) U–Pb carbonate geochronology: strategies, progress, and limitations
Laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) U–Pb carbonate geochronology: strategies, progress, and limitations
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DOI：
10.5194/gchron-2-33-2020
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发表时间：
2020-04
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通讯作者：
N. Roberts;K. Drost;M. Horstwood;D. Condon;D. Chew;H. Drake;A. Milodowski;N. McLean;A. Smye;R. Walker;R. Haslam;K. Hodson;J. Imber;N. Beaudoin;JackKieran Lee
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作者：
N. Roberts;K. Drost;M. Horstwood;D. Condon;D. Chew;H. Drake;A. Milodowski;N. McLean;A. Smye;R. Walker;R. Haslam;K. Hodson;J. Imber;N. Beaudoin;JackKieran Lee
摘要。激光烧蚀电感耦合等离子体质谱法（LA-ICP-MS）对碳酸盐矿物，特别是方解石的U-Pb年代学作为一种绝对测年方法正迅速得到普及。LA-ICP-MS U-Pb碳酸盐岩地质年代学的高空间分辨率优于传统的同位素稀释方法，特别是对于成岩和热液方解石，因为铀和铅在亚毫米尺度上不均匀分布。与此同时，这也给该方法带来了局限性，因为定位放射性铅的区域可能很耗时，而且“命中或不命中”。在这里，我们提出了用原位技术测定碳酸盐岩年代的策略，通过成像和岩石学技术来解释数据；我们的例子来自于裂缝充填方解石的定年，但我们的讨论与所有碳酸盐的应用有关。我们回顾了该方法的几个局限性，包括开放系统行为，可变初始铅组成和u -女儿不平衡。我们还讨论了两种数据收集方法：由岩石学和元素成像指导的传统斑点分析和利用LA-ICP-MS元素和同位素图数据的基于图像的定年。
Abstract. Laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) U–Pb geochronology of carbonate minerals, calcite in particular, is rapidly gaining popularity as an absolute dating method. The high spatial resolution of LA-ICP-MS U–Pb carbonate geochronology has benefits over traditional isotope dilution methods, particularly for diagenetic and hydrothermal calcite, because uranium and lead are heterogeneously distributed on the sub-millimetre scale. At the same time, this can provide limitations to the method, as locating zones of radiogenic lead can be time-consuming and “hit or miss”. Here, we present strategies for dating carbonates with in situ techniques, through imaging and petrographic techniques to data interpretation; our examples are drawn from the dating of fracture-filling calcite, but our discussion is relevant to all carbonate applications. We review several limitations to the method, including open-system behaviour, variable initial-lead compositions, and U–daughter disequilibrium. We also discuss two approaches to data collection: traditional spot analyses guided by petrographic and elemental imaging and image-based dating that utilises LA-ICP-MS elemental and isotopic map data.