Abstract
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-dose non-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.
Highlights
U–Pb geochronology is a widely used radiometric dating tool applied to geological time-scales from 800 thousand years to >4 billion years
As a result of this, U is compatible but Pb is incompatible in the zircon crystal structure, so that common Pb is preferentially excluded at the time of zircon formation, whereas 206Pb and 207 Pb can reside within zircon following in-situ radioactive decay from the parent U isotopes
This study aims to investigate if chemical abrasion can be applied to LA-ICP-MS U–Pb zircon geochronology to reduce discordance
Summary
U–Pb geochronology is a widely used radiometric dating tool applied to geological time-scales from 800 thousand years to >4 billion years. This is made possible due to dual uranium parent isotopes of. Plasma Ionization Mass Spectrometry (LA-ICP-MS) are generally used when there is a requirement for a greater number of analyses at a lower analytical precision, or where a spatially resolved analysis is beneficial. As a result of this, U is compatible but Pb is incompatible in the zircon crystal structure, so that common (or initial) Pb is preferentially excluded at the time of zircon formation, whereas 206Pb and 207 Pb can reside within zircon following in-situ radioactive decay from the parent U isotopes. The exact mode of incorporation and place of residence of radiogenic Pb in the zircon crystal structure is thought to be strongly dependent on composition, such as the presence or absence of phosphate or hydrous phases [6]
Sign-in/Register to view highlights & summary Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
