TY - JOUR

T1 - Xenotime at the Nanoscale

T2 - U-Pb Geochronology and Optimisation of Analyses by Atom Probe Tomography

AU - Joseph, Cilva

AU - Fougerouse, Denis

AU - Saxey, David W.

AU - Verberne, Rick

AU - Reddy, Steven M.

AU - Rickard, William D. A.

N1 - Funding Information: Mounts UWA A‐13 and 05‐12 used in this project are part of the McNaughton Legacy Collection, which was created by the John de Laeter Centre (Brent McInnes – 0000‐0002‐2776‐0574, Eleanore Blereau – 0000‐0001‐8850‐397X and Neal McNaughton), Curtin University Library (Amanda Bellenger, David Lewis, John Brown, and Colin Meikle) and the Geological Survey of Western Australia (Michael Wingate – 0000‐0003‐2528‐417X). The project was jointly enabled by NCRIS via AuScope, GSWA and Curtin University. This study was supported by the Australian Science and Industry Endowment Fund (grant SIEF RI13‐01) and the Discovery Early Career Research Award from the Australian Research Council to D. Fougerouse (DE190101307). Publisher Copyright: © 2021 The Authors. Geostandards and Geoanalytical Research © 2021 International Association of Geoanalysts

PY - 2021

Y1 - 2021

N2 - Xenotime (YPO4) 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 206Pb/238U and 207Pb/206Pb 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 206Pb/238U fractionation and 238UO22+/238UO2+ was used to correct for the atom probe instrument parameters variability between specimens. For 207Pb/206Pb ages, we employed two methods of background correction owing to the 206Pb2+ thermal tail contribution to the 207Pb2+ 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.

AB - Xenotime (YPO4) 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 206Pb/238U and 207Pb/206Pb 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 206Pb/238U fractionation and 238UO22+/238UO2+ was used to correct for the atom probe instrument parameters variability between specimens. For 207Pb/206Pb ages, we employed two methods of background correction owing to the 206Pb2+ thermal tail contribution to the 207Pb2+ 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.

KW - Pb/U

KW - Pb/Pb

KW - APT

KW - atom probe tomography

KW - nanogeochronology

KW - radiometric dating

U2 - 10.1111/ggr.12398

DO - 10.1111/ggr.12398

M3 - Journal article

AN - SCOPUS:85110624301

VL - 45

SP - 443

EP - 456

JO - Geostandards and Geoanalytical Research

JF - Geostandards and Geoanalytical Research

SN - 1639-4488

IS - 3

ER -