Determination of U–Pb Ages for Young Zircons using Laser Ablation‐ICP‐Mass Spectrometry Coupled with an Ion Detection Attenuator Device. Issue 4 (28th November 2014)

• Record Type: Journal Article
• Authors: Sakata, Shuhei; Hattori, Kentaro; Iwano, Hideki; Yokoyama, Takaomi D.; Danhara, Tohru; Hirata, Takafumi
• Is Part Of: Geostandards and geoanalytical research. Volume 38:Issue 4(2014)
• Page Start: 409
• Page End: 420
• Publication Date: 2014-11-28
• Subjects: Analytical geochemistry -- Periodicals; Géochimie analytique -- Périodiques; 551.9
• DOI: 10.1111/j.1751-908X.2014.00320.x
• Languages: English
• ISSNs: 1639-4488

Abstract

<abstract abstract-type="main" id="ggr12045-abs-0005"> <title> <x xml:space="preserve">Abstract</x> </title> <p>We have developed new analytical procedures to measure precise and accurate <sup>238</sup>U–<sup>206</sup>Pb and <sup>235</sup>U–<sup>207</sup>Pb ages for young (~ 1 Ma) zircons using laser ablation‐ICP‐mass spectrometry. For young zircons, both careful correction for the background counts and analysis of very small Pb/U ratios (i.e., <sup>206</sup>Pb/<sup>238</sup>U < 0.00016 and <sup>207</sup>Pb/<sup>235</sup>U < 0.0001 for 1 Ma zircons) are highly desired. For the correction of the background, the contribution of the background signal intensities for the analytes, especially for the residual signal intensities for <sup>206</sup>Pb and <sup>207</sup>Pb, was defined through laser ablation of synthesised zircons (ablation blank) containing negligible Pb. The measured signal intensities for <sup>202</sup>Hg, <sup>206</sup>Pb and <sup>207</sup>Pb signals obtained by the ablation blank were slightly higher than those obtained by data acquisition without laser ablation (gas blank). For the wider dynamic range measurements on Pb/U ratios, an attenuator device for the ion detection system was employed to extend the capability to monitor high‐intensity signals (i.e., > 3 Mcps). Through the attenuator device, the ion currents were reduced to 1/450 of the signal intensity without the attenuator. Because the switching time for the attenuator was shorter than 1 ms, signal intensities for only specific isotopes could be reduced. With attenuation of the <sup>238</sup>U signal, counting statistics on <sup>206</sup>Pb and <sup>207</sup>Pb isotopes could be improved and counting loss on the <sup>238</sup>U signal could be minimised. To demonstrate the reliability of this new analytical technique, <sup>238</sup>U–<sup>206</sup>Pb and <sup>235</sup>U–<sup>207</sup>Pb ages for three young zircon samples (collected from Osaka Group Pink Volcanic Ash, Kirigamine and Bishop Tuff) were measured. The data presented here demonstrate clearly that the present technique could become a major analytical tool for <italic>in situ</italic> U–Pb age determination of young zircons (~ 1 Ma).</p> </abstract>