SS14‐28: An Age Reference Material for Zircon U‐Th Disequilibrium Dating. Issue 1 (16th November 2021)

• Record Type: Journal Article
• Authors: Marsden, Ruby C.; Danišík, Martin; Schmitt, Axel K.; Rankenburg, Kai; Guillong, Marcel; Ahn, Ung‐San; Kirkland, Christopher L.; Evans, Noreen J.; Bachmann, Olivier; Tacchetto, Tommaso; McDonald, Bradley J.; Olierook, Hugo K. H.
• Is Part Of: Geostandards and geoanalytical research. Volume 46:Issue 1(2022)
• Page Start: 57
• Page End: 69
• Publication Date: 2021-11-16
• Subjects: U‐Th‐Pb dating -- zircon -- trachyte -- reference material -- LA‐ICP‐MS -- SIMS; Analytical geochemistry -- Periodicals; Géochimie analytique -- Périodiques; 551.9
• DOI: 10.1111/ggr.12406
• Languages: English
• ISSNs: 1639-4488

Abstract

Abstract : U‐Th disequilibrium dating uses the ratio of the intermediate 230 Th daughter isotope to the 238 U parent isotope to date zircon crystallisation for volcanic and plutonic rocks in Pleistocene–Holocene deposits. It is frequently used to constrain the duration and rate of magma recharge in volcanic systems. While ≲ 350 ka zircon is not in secular equilibrium in the 230 Th system, the current U‐Th disequilibrium methodology uses reference materials that are > 350 ka. No reference material ≲ 350 ka has been available to validate the accuracy of the approach and ensure methods are repeatable across laboratories. This study presents zircon SS14‐28 from Jeju Island (South Korea) as a suitable reference material for U‐Th disequilibrium dating. Zircon SS14‐28 was analysed using two analytical approaches (SIMS and LA‐ICP‐MS) and four instruments: CAMECA IMS 1280, ASI SHRIMP II, sector field high‐resolution LA‐ICP‐MS and multi‐collector LA‐ICP‐MS, in four laboratories. These methods each individually result in isochrons gradients within uncertainty (2 s ) of each other (CAMECA: 0.532 ± 0.051 (MSWD = 0.64); SF‐HR‐LA‐ICP‐MS: 0.536 ± 0.054 (MSWD = 1.3); MC‐LA‐ICP‐MS: 0.533 ± 0.041 (MSWD = 0.67); SHRIMP II: 0.68 ± 0.22 (MSWD = 0.3)). The age proposed in this study is 82 ± 6 ka calculated from a combined isochron gradient of 0.529 ± 0.025 (MSWD = 0.87, n = 132). Abstract : Key Points The age homogeneity and U‐Th mass fraction heterogeneity of zircon SS14‐28 makes it a suitable secondary age reference material for U‐Th disequilibrium dating. Analysis by SIMS and LA‐ICP‐MS (4 instruments in 4 laboratories) gave individual isochron gradients within 2 s of each other. A crystallisation age of 82 ± 6 ka was determined from an isochron gradient of 0.529 ± 0.025.