Chemical Abrasion Applied to LA-ICP-MS U–Pb Zircon Geochronology

Minerals

David Chew¹  Quentin G. Crowley¹  Kyle Heron¹  Balz Kamber¹  Brian McConnell²  Nancy Riggs³  Keith Benn⁴ 

[1] Department of Geology, School of Natural Sciences, Trinity College, Dublin 2, Ireland;Geological Survey of Ireland, Beggars Bush, Dublin 4, Ireland;School of Earth Sciences and Environmental Sustainability, Northern Arizona University, Flagstaff, AZ 86011, USA;Tasiast Mauritanie Limited SA, ZRA 741, BP 5051, Nouakchott, Mauritania, West Africa;

关键词: U–Pb geochronology;    zircon;    chemical abrasion;    Laser Ablation Inductively Coupled Plasma Mass Spectrometry (LA-ICP-MS);    Pb-loss;   

DOI  :  10.3390/min4020503

来源: DOAJ

【 摘 要 】

Zircon (ZrSiO4) is the most commonly used mineral in U–Pb geochronology. Although it has proven to be a robust chronometer, it can suffer from Pb-loss or elevated common Pb, both of which impede precision and accuracy of age determinations. Chemical abrasion of zircon involves thermal annealing followed by relatively low temperature partial dissolution in HF acid. It was specifically developed to minimize or eliminate the effects of Pb-loss prior to analysis using Thermal Ionization Mass Spectrometry (TIMS). Here we test the application of chemical abrasion to Laser Ablation Inductively Coupled Plasma Mass Spectrometry (LA-ICP-MS) by analyzing zircons from both untreated and chemically abraded samples. Rates of ablation for high alpha-dosenon-treated zircons are up to 25% faster than chemically abraded equivalents. Ablation of 91500 zircon reference material demonstrates a ca. 3% greater down-hole fractionation of 206Pb/238U for non-treated zircons. These disparities necessitate using chemical abrasion for both primary reference material and unknowns to avoid applying an incorrect laser induced fractionation correction. All treated samples display a marked increase in the degree of concordance and/or lowering of common Pb, thereby illustrating the effectiveness of chemical abrasion to LA-ICP-MS U–Pb zircon geochronology.

【 授权许可】

Unknown