Zircon U-Pb chemical abrasion ("CA-TIMS") method: Combined annealing and multi-step partial dissolution analysis for improved precision and accuracy of zircon ages
Zircon U-Pb chemical abrasion ("CA-TIMS") method: Combined annealing and multi-step partial dissolution analysis for improved precision and accuracy of zircon ages
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DOI：
10.1016/j.chemgeo.2005.03.011
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发表时间：
2005-07-12
期刊：
影响因子：
3.9
通讯作者：
Mattinson, JM
中科院分区：
文献类型：
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作者：
Mattinson, JM
高精度、高精度锆石U-Pb年代学的一个长期目标是完全消除Pb损失引起的不一致。从理论上讲，这是相当简单的，但在现实中，它已被证明是非常困难的，以达到（甚至证明达到）这一目标。然而，一种新的方法，“CA（化学磨蚀）-TIMS”，能够完全去除已经失去铅的锆石域，然后分析残留的，完全封闭系统的锆石。CA-TIMS使用高温处理（在800-1100摄氏度范围内持续48小时）来退火来自自然α、α反冲和自发裂变过程的锆石晶格辐射损伤;这种退火消除了元素和同位素浸出效应，这些效应限制了早期在化学“浸出”或多步“逐步溶解”或“部分溶解分析（PDA）"方面的努力。然后，退火的锆石在逐渐升高的温度下经历一系列部分溶解步骤。这些步骤最初去除（通常是外部）具有高U+Th浓度的锆石区。由于Ph损失，这些最早的部分溶解步骤总是轻微到强烈不一致。随后的步骤样品逐渐降低U + Th锆石域。在缺乏继承性的锆石样品中，这些后续步骤对完全没有Pb损失的锆石区域进行取样，以优于0.1%的精度（和精度，受衰变常数和示踪剂校准精度的影响）确定Pb-206*/U-238平台年龄。(c)2005 Elsevier B. V.保留所有权利。
A long-standing goal in high-precision and high-accuracy U-Pb zircon geochronology is the total elimination of discordance caused by Pb loss. In theory, this is fairly straightforward, but in reality it has proven extremely difficult to attain (or even demonstrate attainment of) this goal. However, a new method, "CA (Chemical Abrasion)-TIMS", is capable of completely removing zircon domains that have lost Pb, and then analyzing residual, perfectly closed-system zircon. CA-TIMS uses high-temperature treatment (in the range of 800-1100 degrees C for 48 h) to anneal zircon lattice radiation damage from natural alpha, alpha recoil, and spontaneous fission processes; this annealing eliminates elemental and isotopic leaching effects that have limited earlier efforts at chemical "leaching" or multi-step "step-wise dissolution" or "partial dissolution analysis (PDA)". The annealed zircons are then subjected to a series of partial dissolution steps at progressively higher temperatures. These steps initially remove (usually outer) zircon zones with high U+Th concentrations. These earliest partial dissolution steps are invariably slightly to strongly discordant, due to Ph loss. Later steps sample progressively lower U + Th zircon domains. In zircon samples that lack inheritance, these later steps sample zircon domains that are completely free from Pb loss, defining Pb-206*/U-238 plateau ages with precisions (and accuracies, subject to decay constant and tracer calibration accuracies) better than 0.1%. (c) 2005 Elsevier B.V. All rights reserved.