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Xenotime at the Nanoscale: U‐Pb Geochronology and Optimisation of Analyses by Atom Probe Tomography
Author(s) -
Joseph Cilva,
Fougerouse Denis,
Saxey David W.,
Verberne Rick,
Reddy Steven M.,
Rickard William D. A.
Publication year - 2021
Publication title -
geostandards and geoanalytical research
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.037
H-Index - 73
eISSN - 1751-908X
pISSN - 1639-4488
DOI - 10.1111/ggr.12398
Subject(s) - geochronology , geology , archean , atom probe , mineralogy , materials science , geochemistry , microstructure , metallurgy
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.