Dating Micrometre‐Thin Rims Using a LA‐ICP‐MS Depth Profiling Technique on Zircon from an Archaean Metasediment: Comparison with the SIMS Depth Profiling Method |
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Authors: | Colter J Kelly Christopher RM McFarlane David A Schneider Simon E Jackson |
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Institution: | 1. Department of Earth Sciences, University of Ottawa, , Ottawa, K1N 6N5, Canada;2. Department of Earth Sciences, University of New Brunswick, , Fredericton, E3B 5A3 Canada;3. Natural Resources Canada, Geological Survey of Canada, , Ottawa, K1A 0E4 Canada |
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Abstract: | Laser ablation‐inductively coupled plasma‐mass spectrometry (LA‐ICP‐MS) was examined as a tool for measuring isotopic variation as a function of ablation depth in unpolished zircon from an Archaean metasediment specimen. This technique was able to identify micrometre‐thin (> 3 μm) isotopically distinct mineral domains characterised by ca. 100 Myr younger 207Pb/206Pb ages associated with 2s age uncertainties as low ~ 0.2%, as well as elevated U content relative to grain interiors (up to an order of magnitude). Our calculated drilling rate suggests that each laser pulse excavated depths of ~ 0.06 μm. Ages resolved through the LA‐ICP‐MS methods overlap the 2s uncertainties of 207Pb/206Pb ages measured using SIMS depth profiling on the same zircon population. The rims were further evinced by the detection of relative enrichment (> 3 orders of magnitude) in REE in the outermost micrometres of the same zircon, measured using a different and independent LA‐ICP‐MS depth profiling technique. We propose a LA‐ICP‐MS U–Pb technique capable of quickly identifying and quantifying rims, which are indication of late, yet geologically significant, fluid events that are otherwise undefined. |
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Keywords: | geochronology LA‐ICP‐MS depth profile zircon
REE
SIMS
Gé ochronologie LA‐ICP‐MS profil en profondeur zircon REE SIMS |
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