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Observation of centimetre-scale argon diffusion in alkali feldspars: implications for 40Ar/39Ar thermochronology

By
Stephanie Flude
Stephanie Flude
1
Department of Earth and Environmental Sciences, The Open University, CEPSAR, Walton Hall, Milton Keynes MK7 6AA, UK
2
Present address: QUADLAB, ENSPAC 12.1, Roskilde University, 4000 Roskilde, Denmark
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Alison M. Halton
Alison M. Halton
1
Department of Earth and Environmental Sciences, The Open University, CEPSAR, Walton Hall, Milton Keynes MK7 6AA, UK
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Simon P. Kelley
Simon P. Kelley
1
Department of Earth and Environmental Sciences, The Open University, CEPSAR, Walton Hall, Milton Keynes MK7 6AA, UK
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Sarah C. Sherlock
Sarah C. Sherlock
1
Department of Earth and Environmental Sciences, The Open University, CEPSAR, Walton Hall, Milton Keynes MK7 6AA, UK
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James Schwanethal
James Schwanethal
1
Department of Earth and Environmental Sciences, The Open University, CEPSAR, Walton Hall, Milton Keynes MK7 6AA, UK
3
Present address: London Geochronology Centre, Department of Earth Sciences, University College London, Gower Street, London WC1E 6BT, UK
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Camilla M. Wilkinson
Camilla M. Wilkinson
1
Department of Earth and Environmental Sciences, The Open University, CEPSAR, Walton Hall, Milton Keynes MK7 6AA, UK
4
Present address: Geological Survey of Norway, P. O. Box 6315, Sluppen, NO-7491, Trondheim, Norway
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Published:
January 01, 2014

Abstract

New data from a gem-quality feldspar from Itrongay, Madagascar, record naturally occurring 40Ar/39Ar age profiles which can be numerically modelled by invoking a single diffusion mechanism and show that microtexturally simple crystals are capable of recording complex thermal histories. We present the longest directly measured, naturally produced 40Ar*-closure profiles from a single, homogeneous orthoclase feldspar. These data appear to confirm the assumption that laboratory derived diffusion parameters are valid in nature and over geological timescales. Diffusion domains are defined by crystal faces and ancient cracks, thus in gem-quality feldspars the diffusion domain size equates to the physical grain size. The data also illustrate the potential of large, gem-quality feldspars to record detailed thermal histories over tens of millions of years and such samples should be considered for future studies on the slow cooling of continental crust.

Supplementary material:

Ar-isotope data, standards and constants used in calculations and irradiation parameters are available at http://www.geolsoc.org.uk/SUP18720.

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Contents

Geological Society, London, Special Publications

Advances in 40Ar/39Ar Dating: From Archaeology to Planetary Sciences

F. Jourdan
F. Jourdan
Curtin University, Australia
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D. F. Mark
D. F. Mark
Scottish Universities Environmental Research Centre, UK
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C. Verati
C. Verati
University of Nice, France
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Geological Society of London
Volume
378
ISBN electronic:
9781862396623
Publication date:
January 01, 2014

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