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

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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.