Xenotime at the Nanoscale: U‐Pb Geochronology and Optimisation of Analyses by Atom Probe Tomography

Abstract

Xenotime (YPO 4 ) is an accessory phase common in low to high-temperature geological environments. Xenotime is an established geochronometer, though its small size, low modal abundance and textural complexity make it more difficult to analyse with traditional techniques but makes a prime candidate for nanoscale analysis. In this study, we develop an atom probe tomography (APT) protocol to determine the 206 Pb/ 238 U and 207 Pb/ 206 Pb ages of micro-scale xenotime crystals with analytical volumes four to six orders of magnitude smaller than typical geochronology techniques. A linear correlation between the 206 Pb/ 238 U fractionation and 238 UO 2 2+ / 238 UO 2+ was used to correct for the atom probe instrument parameters variability between specimens. For 207 Pb/ 206 Pb ages, we employed two methods of background correction owing to the 206 Pb 2+ thermal tail contribution to the 207 Pb 2+ counts: A constant background correction for the younger (~1000 Ma) Y1 reference material and a variable correction of background for Archaean age reference material xtc to correct for the thermal tail influence. This contribution also proposes strategies for optimisation of xenotime analysis using APT and permits us to explore the various geological problems in the nanoscale realm. This methodology potentially allows determining the age of small xenotime crystals in sedimentary rocks, low metamorphic grade settings and deformation microstructures.

Atomic spectrometry update – a review of advances in environmental analysis

“…There has been much research activity focused on the U–Pb dating of accessory minerals other than zircon by microanalytical techniques. Minerals investigated included: apatite 245 by LA-ICP-MS/MS, carbonates 246 by LA-MC-ICP-MS, cassiterite 247 by LA-SF-ICP-MS, garnet 248 by SIMS, ilmenite 249 by LA-ICP-MS, rutile 250 by LA-ICP-MS, scheelite 251 by LA-SF-ICP-MS, titanite 250,252 by LA-ICP-MS and SIMS, vesuvianite 253 by LA-SF-ICP-MS, wolframite 254 by LA-ICP-MS and xenotime 255 by APT. The continued development of U–Pb dating methods to a wide range of minerals is fundamental in increasing the number of geochronological tools available for unravelling geological processes.…”

Standardizing Spatial Reconstruction Parameters for the Atom Probe Analysis of Common Minerals

“…Xenotime is routinely used as a U-Th-Pb geochronometer and a petrogenetic indicator (Spear & Pyle, 2002; Fletcher et al, 2004). Protocol has been developed to define APT 206 Pb/ 238 U and 207 Pb/ 206 Pb ages of xenotime (Joseph et al, 2021). A fragment of the xenotime BS-1 reference material (Fletcher et al, 2004) was prepared in a resin mount and polished.…”

“…New applications of APT in the Earth and planetary sciences have spanned a wide range of minerals of various crystallography and chemistry. However, only a few studies have aimed at defining standard practices for data acquisition, spectral processing, and reporting (Blum, Reinhard et al, 2018; Blum, Darling et al, 2018; La Fontaine et al, 2017; Exertier et al, 2018; Saxey et al, 2018; Verberne et al, 2019; Fougerouse et al, 2020; Joseph et al, 2021).…”

Nanoscale features revealed by a multiscale characterisation of discordant monazite highlight mobility mechanisms of Th and Pb

“…Evidence of mineralogical processes that affect geochronometers and that induce element mobility may be recorded within the crystal. The benefits of examining geochronometers at the nanoscale using transmission electron microscopy (TEM) and atom probe tomography (APT) to address broader issues of element mobility has been demonstrated for zircon (Utsunomiya et al 2004;Kusiak et al 2015Kusiak et al , 2019Valley et al 2015;Peterman et al 2016Peterman et al , 2019Piazolo et al 2016;Whitehouse et al 2017), monazite (Seydoux-Guillaume et al 2003Fougerouse et al 2018Fougerouse et al , 2021aBudzyń et al 2021Budzyń et al , 2022Turuani et al 2022), rutile (Verberne et al 2020), xenotime (Joseph et al 2021;Budzyń et al 2023) and baddeleyite (White et al 2017).…”

“…Several processes promoting Pb mobility at the nanoscale, all with the potential to leave behind nanoscale features (cluster, nanophases) operate within monazite. A variety of such features have been recognized (Seydoux-Guillaume et al 2003;Fougerouse et al 2018Fougerouse et al , 2021Turuani et al 2022) but have not, as yet, been studied systematically in a single sample so that their significance and potential use for nanoscale geochronology can be assed in detail.…”