Collaborative Research: Development of Improved Zircon Standards for SIMS and LA-ICP-MS-U-Pb Geochronology using CA-TIMS Pre-Treatment

部分开放体系行为是限制锆石U-Pb年代学准确度的主要因素。最近开发的Mattinson(2005)的化学磨损TIMS(CA-TIMS)包括在部分溶解实验之前通过一系列日益激进的浸出步骤对辐射损伤进行热退火，这显示出在近协调的锆石群体中完全消除(在早期溶解步骤中)高U、Pb损失域的技术的巨大前景。微束技术，如SIMS和LA-ICPMS，依赖于对表征良好的锆石的外部标准化，其闭合系统行为已经在多颗粒TIMS分析的基础上被证明。该项目的目标有两个：1)检验假设，即用CA-TIMS方法表征和清理的等分锆石比现有的受轻微铅损失影响的未处理等分锆石可以更好地监测微束仪器的行为；2)产生大量经过处理的准合成锆石标准品，供SIMS和LA-ICPMS实验室分配，以提高未知样品现场分析的外部精确度。一套改进的锆石标准将在SIMS和LA-ICPMS实验室之间分发，这是对地质年代学社区的一项重大服务。该项目为职业生涯早期的地球科学家(Hourigan)提供支持。此外，分析预算为UCSB同位素比质谱分析实验室的日常运营提供了设施支持，该实验室有多名研究生。本科生将从参与分析工作中受益。

Partially open system behavior is a major factor limiting accuracy in zircon U-Pb geochronology. The recently developed chemical abrasion TIMS (CA-TIMS) of Mattinson (2005) involving thermal annealing of radiation damage prior to partial dissolution experiments through a series of increasingly aggressive leaching steps shows great promise as technique for complete removal (during early dissolution steps) of high-U, Pb-loss domains within near-concordant zircon populations. Microbeam techniques such as SIMS and LA-ICP-MS rely on external standardization to well-characterized zircon for which closed system behavior has been demonstrated on the basis of multi-grain TIMS analyses. The goals of this project are twofold: 1) to test the hypothesis that aliquots of zircon characterized and cleaned-up with the CA-TIMS method function as better monitors of microbeam instrument behavior than extant untreated aliquots which are affected by minor Pb loss; 2) to produce large aliquots of treated quasi-synthetic zircon standards for distribution amongst SIMS and LA-ICP-MS labs to improve the external precision of in situ analyses of unknown samples. A suite of improved zircon standards will be distributed amongst SIMS and LA-ICP-MS labs alike representing a significant service to the geochronologic community. The project provides support for an early career geoscientist (Hourigan). Furthermore, the analytical budget provides facilities support for day-to-day operation of the UCSB Isotope Ratio Mass Spectrometry Lab which is staffed by multiple graduate students. Undergraduates will benefit through participation in analytical work.