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年代学精度的主要因素。Mattinson（2005）最近开发的化学磨损TIMS (CA-TIMS)，包括通过一系列日益激烈的浸出步骤，在部分溶解实验之前对辐射损伤进行热退火，作为在接近一致的锆石群体中（在早期溶解步骤中）完全去除高u， pb损失域的技术，显示出巨大的前景。SIMS和LA-ICP-MS等微束技术依赖于外部标准化来表征锆石，其封闭系统行为已在多粒TIMS分析的基础上得到证实。该项目的目的有两个：1)验证用CA-TIMS方法表征和清理的锆石同质石比现有的未经处理的受微量铅损失影响的同质石能更好地监测微束仪器行为的假设；2)生产大量处理后的准合成锆石标准品，在SIMS和LA-ICP-MS实验室中分发，以提高未知样品原位分析的外部精度。一套改进的锆石标准将分发给SIMS和LA-ICP-MS实验室，代表着对地质年代学界的重要服务。该项目为早期职业地球科学家提供支持（Hourigan）。此外，分析预算为UCSB同位素比质谱实验室的日常运作提供设施支持，该实验室由多名研究生组成。本科生将通过参与分析工作而受益。

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.