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Mud Tank Zircon: Long‐Term Evaluation of a Reference Material for U‐Pb Dating, Hf‐Isotope Analysis and Trace Element Analysis
Author(s) -
Gain Sarah E. M.,
Gréau Yoann,
Henry Hadrien,
Belousova Elena,
Dainis Ivars,
Griffin William L.,
O'Reilly Suzanne Y.
Publication year - 2019
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.12265
Subject(s) - zircon , trace element , isotope analysis , geology , rare earth element , isotope , mineralogy , inductively coupled plasma mass spectrometry , homogeneous , chemistry , geochemistry , mass spectrometry , rare earth , physics , quantum mechanics , oceanography , chromatography , thermodynamics
Zircon megacrysts from the Mud Tank carbonatite, Australia, are being used in many laboratories as a reference material for LA ‐ ICP ‐ MS U‐Pb dating and trace element measurement, and LA ‐ MC ‐ ICP ‐ MS determination of Hf isotopes. We summarise a database of > 10000 analyses of Mud Tank zircon (MTZ), collected from 2000 to 2018 during its use as a secondary reference material for simultaneous U‐Pb and trace element analysis, and for Hf‐isotope analysis. Trace element mass fractions are highest in dark red‐brown stones and lowest in colourless and gem‐quality ones. Individual unzoned grains can be chemically homogeneous, while significant variations in trace element mass fraction are associated with oscillatory zoning. Chondrite‐normalised trace element patterns are essentially parallel over large mass fraction ranges. A Concordia age of 731.0 ± 0.2 Ma (2 s , n = 2272) is taken as the age of crystallisation. Some grains show lower concordant to mildly discordant ages, probably reflecting minor Pb loss associated with cooling and the Alice Springs Orogeny (450–300 Ma). Our weighted mean 176 Hf/ 177 Hf is 0.282523 ± 10 (2 s , n = 9350); the uncertainties on this ratio reflect some heterogeneity, mainly between grains. A few analyses suggest that colourless grains have generally lower 176 Hf/ 177 Hf. MTZ is a useful secondary reference material for U‐Pb and Hf‐isotope analysis, but individual grains need to be carefully selected using CL imaging and tested for homogeneity, and ideally should be standardised by solution analysis.