Tephrochronology is one of the most effective ways to correlate and date Quaternary deposits across large distances. However, it can be challenging to obtain direct ages on tephra beds when they are beyond the limit of radiocarbon dating, do not contain mineral phases suitable for ⁴⁰K-⁴⁰Ar (or ⁴⁰Ar/³⁹Ar) dating, or suitable glass shards for fission-track dating are not available. Zircon U-Pb dating by laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS) is an emerging technique for dating young (<1 Ma) tephra. Here, we demonstrate that LA-ICP-MS zircon U-Pb dating can produce reliable ages for key tephra beds found in Yukon and Alaska. We assessed five different techniques for calculating tephra maximum depositional ages from zircon U-Pb ages for eight tephra beds. Our preferred zircon U-Pb ages (reported with 2σ uncertainties), based on a Bayesian model for calculating maximum depositional ages, are broadly consistent with previously established chronology constructed from stratigraphy, paleomagnetism, and/or glass fission track and ⁴⁰Ar/³⁹Ar ages: Biederman tephra (178 ± 17 ka), HP tephra (680 ± 47 ka), Gold Run tephra (688 ± 44 ka), Flat Creek tephra (708 ± 43 ka), PA tephra (1.92 ± 0.06 Ma), Quartz Creek tephra (2.62 ± 0.08 Ma), Lost Chicken tephra (3.14 ± 0.07 Ma), and GI tephra (542 ± 64 ka). We also present newly revised glass fission-track and ⁴⁰Ar/³⁹Ar ages recalculated from previous determinations using updated ages for the Moldavite tektite and Fish Canyon Tuff standards, and updated K decay constants. For Pleistocene age zircon crystals, corrections for ²³⁰Th disequilibrium and common-Pb are significant and must be treated with caution. Similarly, apparent tephra ages are sensitive to the choice of method used to calculate a maximum depositional age from the assemblage of individual crystallization ages. This study demonstrates that LA-ICP-MS zircon U-Pb dating can be successfully applied to numerous Pliocene-Pleistocene Alaskan-Yukon tephra, providing confidence in applying this method to other stratigraphically important tephra in the region.

年代学是跨远距离关联和确定第四纪沉积物年代的最有效方法之一。然而，当火山灰岩层超出放射性碳测年限制、不包含适合⁴⁰ K- ⁴⁰ Ar（或⁴⁰ Ar/ ³⁹Ar) 测年，或适合裂变轨道测年的玻璃碎片不可用。通过激光烧蚀电感耦合等离子体质谱法 (LA-ICP-MS) 进行锆石 U-Pb 测年是一种用于测年年轻 (<1 Ma) 火山灰的新兴技术。在这里，我们证明 LA-ICP-MS 锆石 U-Pb 测年可以为育空和阿拉斯加发现的关键火山岩层提供可靠的年龄。我们评估了五种不同的技术，用于从 8 个火山岩层的锆石 U-Pb 年龄计算火山岩最大沉积年龄。我们首选的锆石 U-Pb 年龄（以 2σ 不确定性报告），基于用于计算最大沉积年龄的贝叶斯模型，与先前建立的由地层学、古地磁学和/或玻璃裂变轨迹和⁴⁰ Ar/ ^{39构建的年代学大致一致}Ar年龄：Biederman tephra (178 ± 17 ka), HP tephra (680 ± 47 ka), Gold Run tephra (688 ± 44 ka), Flat Creek tephra (708 ± 43 ka), PA tephra (1.92 ± 0.06 Ma), Quartz Creek tephra (2.62 ± 0.08 Ma)、Lost Chicken tephra (3.14 ± 0.07 Ma) 和 GI tephra (542 ± 64 ka)。我们还展示了新修订的玻璃裂变轨迹和⁴⁰ Ar/ ³⁹ Ar 年龄，这些年龄是使用更新的陨石陨石和鱼峡谷凝灰岩标准的年龄和更新的 K 衰变常数从以前的测定中重新计算的。对于更新世锆石晶体，校正为²³⁰Th 不平衡和常见的 Pb 是显着的，必须谨慎对待。类似地，表观火山灰年龄对用于从单个结晶年龄的组合计算最大沉积年龄的方法的选择很敏感。本研究表明，LA-ICP-MS 锆石 U-Pb 测年可成功应用于众多上新世-更新世阿拉斯加-育空火山灰，为将该方法应用于该地区其他重要地层的火山灰提供了信心。