Combined U-Pb geochronology and Sr-Nd isotope analysis of the Ice River perovskite standard, with implications for kimberlite and alkaline rock petrogenesis

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• 作者：Sebastian Tappe^a ; ^{sebastian.tappe@uni-muenster.de} ; Antonio Simonetti^b
• 关键词：Ice River perovskite ; Natural mineral standard ; Isotope dilution mass spectrometry ; U&ndash ; Pb geochronology ; Sr&ndash ; Nd isotope geochemistry ; Canadian Cordillera
• 刊名：Chemical Geology
• 出版年：2012
• 期刊代码：12_00092541
• 类别：ear
• 出版时间：18 April, 2012
• 卷：304-305
• 期：Complete
• 页码：10-17
• 文件大小：629 K

摘要

Growing interest in the mineral perovskite (CaTiO₃) as a U-Pb chronometer and archive of near-primary Sr and Nd isotope compositions in magmatic systems highlights the need for well-characterized mineral standards. Based on a conventionally determined, high-precision Sr and Nd isotope data set, we propose perovskite from the alkaline Ice River intrusion as a natural reference material for Sr and Nd isotope ratio determinations. Ice River perovskite has mean present-day ⁸⁷Sr/⁸⁶Sr (TIMS) and ¹⁴³Nd/¹⁴⁴Nd (ID-MC-ICP-MS) ratios of 0.702838 卤 51 and 0.512581 卤 32, respectively (2-sigma uncertainties). The TIMS ²⁰⁶Pb/²³⁸U age of 361.7 卤 1.0 Ma (2-sigma), determined on the same crystal fragments as the Sr and Nd isotope compositions, falls within the accepted range of 355-372 Ma for the Ice River intrusion. Although there is a ~ 2.2%difference between the ages of Ice River perovskite (~ 355-363 Ma) reported in various U-Pb studies (determined by TIMS, SIMS, and LA-MC-ICP-MS methods), the material investigated here has the currently best-calibrated U-Pb systematics for perovskite. We therefore recommend the ²⁰⁶Pb/²³⁸U age of 361.7 卤 1.0 Ma as a reference value for use in geochronology studies.

Perovskite is a prime target for petrogenetic studies of kimberlites and related alkaline rocks, because it preserves primary magmatic signatures. The ability to combine important petrogenetic information with high-resolution U-Pb emplacement ages at mineral scale will be instrumental for an improved understanding of deep magmatism beneath cratons and areas of rifted continental lithosphere.