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Improving precision of Sm-Nd garnet dating by H2SO4 leaching: a simple solution to the phosphate inclusion problem

By
Robert Anczkiewicz
Robert Anczkiewicz
1
University College London
Gower Street, London WC1E 6BT, UK
rob@gl.rhul.ac.uk
2
Institute of Geological Sciences, Polish Academy of Sciences, Kraków Research Centre
ul. Senacka 1, 30-001 Kraków, Poland
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Matthew F. Thirlwall
Matthew F. Thirlwall
3
Department of Geology, Royal Holloway, University of London
Egham, Surrey, TW20 0EX, UK
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Published:
January 01, 2003

Abstract

Sm-Nd garnet geochronology is often hampered by the presence of submicroscopic inclusions of rare earth element-rich phosphates, which lower age precision, lead to inaccurate ages or make dating impossible. We propose a single-step sulphuric acid leaching technique as a very efficient tool in eliminating phosphate inclusions, which helps to achieve more precise and more accurate Sm-Nd garnet dates. Examples from silimanite grade metapelites demonstrate the much higher efficiency of this method in comparison with previously proposed techniques based on HF and HCl. 147Sm/144Nd ratios obtained on garnets leached by sulphuric acid were twice as high as those obtained by HF and HCl leaching. This led to age precision better than 3% for Tertiary samples. Comparison of leached and unleached nearly inclusion-free garnets from high pressure granulites, demonstrates that there is no Sm/Nd fractionation induced by H2SO4 leaching. Our new technique eliminates phosphates, but does not attack garnet. This considerably reduces the necessity for hand-picking and lowers the amount of sample required for analysis making Sm-Nd garnet dating a more easily applied geochronometer.

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Contents

Geological Society, London, Special Publications

Geochronology: Linking the Isotopic Record with Petrology and Textures

D. Vance
D. Vance
Royal Holloway
University of London, UK
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W. Müller
W. Müller
The Australian National University
Australia
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I. M. Villa
I. M. Villa
University of Bern
Switzerland
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Geological Society of London
Volume
220
ISBN electronic:
9781862394681
Publication date:
January 01, 2003

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