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

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.

Muztaghata Dome Miocene Eclogite Facies Metamorphism: A Record of Lower Crustal Evolution of the NE Pamir

“…While our Sm-Nd ages document peak metamorphism as Cenozoic in ages, the dominance of Jurassic U-Pb zircon ages from the western terrane raise interesting questions on the behavior of zircon growth in the dome, as well as whether this event is recorded throughout the dome, that is, the eastern orthogneiss terrane. To investigate these issues, we employed LA-ICP-MS depth profile analysis (e.g., Kelly et al, 2014) on zircon from the terranes of Muztaghata dome. Figure 7.…”

“…Tectonics LA-ICP-MS depth profiling of unpolished zircon grains is an effective method to date micron thick metamorphic zircon rims, yielding robust U-Pb ratios and REE concentrations within~1 um thickness intervals from zircon rims to interiors, and avoiding mixing age domains (Cottle et al, 2009;Kelly et al, 2014). Zircon grains were separated from rock samples via conventional crushing, density, and magnetic methods.…”

High-spatial resolution dating of monazite and zircon reveals the timing of subduction–exhumation of the Vaimok Lens in the Seve Nappe Complex (Scandinavian Caledonides)

“…Zircon depth-profiling, using either Laser Ablation Inductively Coupled Mass Spectrometry (LA-ICP-MS) or Secondary Ion Mass Spectrometry (SIMS), has proven to be a powerful technique to extract radiogenic isotopes and trace elements from micrometerscale rims (e.g. Breeding et al 2004;Kelly et al 2014Kelly et al , 2017Marsh and Stockli 2015;Schneider et al 2011;Skipton et al 2016;Woodhead et al 2004). We applied these techniques to accessory phases hosted in the (U)HP rocks of the Seve Nappe Complex (SNC), Scandinavian Caledonides (Fig.…”

Atomic spectrometry update – a review of advances in environmental analysis

“…Kelly et al 401 investigated the effectiveness of depth proling using laser ablation as an alternative to SIMS for measuring changes in mineral chemistry or age as a function of depth. Use of a single-pulse approach rather than continuous ablation made it possible to reduce the volume of material analysed by LA-ICP-MS to levels required for SIMS analysis.…”