Improving U-Th-Pb electron microprobe dating using monazite age references
Improving U-Th-Pb electron microprobe dating using monazite age references
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DOI：
10.1016/j.chemgeo.2018.02.014
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发表时间：
2018-05
期刊：
影响因子：
3.9
通讯作者：
P. Konečný;M. Kusiak;D. Dunkley
中科院分区：
文献类型：
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作者：
P. Konečný;M. Kusiak;D. Dunkley
本文提出了一种改进的独居石电子探针测年方法，其中包括独居石年龄参考校正(MARC)。在分析过程中，在会议开始时测量一组具有已确定的同位素年龄的不同独居石标准物质。这些测量用于测试分析设置，如有必要，还可计算可应用于独居石样品的MARC因子。MARC的目的不是为了纠正由于设置问题造成的系统性错误，而是为了对单届会议期间不容易评估的因素进行精细调整。对MARC因子的长期、多时段计算允许在各个时段内精确监测独居石年龄参考物质中的异常行为。该方法还可以帮助识别独居石中的化学不均质性，例如通常由于与交代流体相互作用而产生的化学不均质性。介绍了一套具有代表性的电子探针独居石年龄标准物质，其中包括两个独居石的参考独居石，它们是独居石交代引起年龄扰动的很好的例子。提出了对分析方案的其他修改，包括a)对长束停留时间期间的计数速率增加的校正，以及b)通过考虑平均原子序数的影响来改进线位置处的背景值的估计。
This article proposes an improved approach to monazite dating by electron microprobe that includes a “monazite age reference correction” (MARC). During analysis, a set of differing monazite standard reference materials with established isotopic ages are measured at the start of the session. These measurements are used to test the analytical set-up and, if necessary, to calculate MARC factors that can be applied to monazite samples. The MARC is not intended as a way to correct systematic errors due to problems in set-up, but rather as a fine-scale adjustment for factors that cannot be readily assessed during single sessions. Long-term, multi-session calculation of MARC factors allows for precise monitoring of anomalous behavior among monazite age reference materials during individual sessions. The method can also assist in the identification of chemical inhomogeneity in monazite, such as that commonly produced by interaction with metasomatic fluids. A representative set of electron microprobe monazite age reference materials are presented, including two ‘reference monazites’ that are good examples of monazite with age disturbance induced by metasomatism. Additional modifications to analytic protocols are proposed, including a) corrections for count rate increases during long beam dwell times, and b) improved estimation of background values at line positions by accounting for the effect of mean atomic number.