Excess <sup>40</sup>Ar in Alkali Feldspar and <sup>206,207</sup>Pb in Apatite Caused by Fluid-Induced Recrystallisation in a Semi-Closed Environment in Proterozoic (Meta)Granites of the Mt Isa Inlier, NE Australia

Interpretation of <sup>40</sup>Ar/<sup>39</sup>Ar dates of alkali feldspar and U-Pb dates of apatite depends on the dominant mechanism of isotopic transport in these minerals, which can be either diffusion or fluid-assisted dissolution-reprecipitation. To clarify the contribu...

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Main Authors: Daniil Popov, Richard Spikings, André Navin Paul, Maria Ovtcharova, Massimo Chiaradia, Martin Kutzschbach, Alexey Ulianov, Gary O’Sullivan, David Chew, Kalin Kouzmanov, Eszter Badenszki, J. Stephen Daly, Joshua H. F. L. Davies
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Language:English
Published: MDPI AG 2024-12-01
Series:Geosciences
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Online Access:https://www.mdpi.com/2076-3263/14/12/358
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author Daniil Popov
Richard Spikings
André Navin Paul
Maria Ovtcharova
Massimo Chiaradia
Martin Kutzschbach
Alexey Ulianov
Gary O’Sullivan
David Chew
Kalin Kouzmanov
Eszter Badenszki
J. Stephen Daly
Joshua H. F. L. Davies
author_facet Daniil Popov
Richard Spikings
André Navin Paul
Maria Ovtcharova
Massimo Chiaradia
Martin Kutzschbach
Alexey Ulianov
Gary O’Sullivan
David Chew
Kalin Kouzmanov
Eszter Badenszki
J. Stephen Daly
Joshua H. F. L. Davies
author_sort Daniil Popov
collection DOAJ
description Interpretation of <sup>40</sup>Ar/<sup>39</sup>Ar dates of alkali feldspar and U-Pb dates of apatite depends on the dominant mechanism of isotopic transport in these minerals, which can be either diffusion or fluid-assisted dissolution-reprecipitation. To clarify the contributions of these processes, we have conducted a holistic study of alkali feldspar, apatite and other minerals from the Mt. Isa Inlier in NE Australia. Mineral characterisation by electron microscopy, optical cathodoluminescence imaging and element mapping reveal a complex interplay of textures resulting from magmatic crystallisation, deuteric recrystallisation, local deformation with subsequent higher-temperature alteration, and finally ubiquitous low-temperature alteration. U-Pb and Pb isotopic data for zircon, apatite, fluorite and alkali feldspar suggest that the latter event occurred at ~300 Ma and was associated with fluid-assisted exchange of Pb isotopes between minerals in the same rock, causing some apatite grains to have <sup>207</sup>Pb-corrected U-Pb dates that exceed their crystallisation age. However, this event had no unequivocal effect on the <sup>40</sup>Ar/<sup>39</sup>Ar or Rb-Sr systematics of the alkali feldspar, which were disturbed by higher-temperature alteration at ~1450 Ma. The age of the latter event is derived from Rb-Sr data. <sup>40</sup>Ar/<sup>39</sup>Ar dates are very scattered and suggest that <sup>40</sup>Ar redistribution proceeded by diffusion in the presence of traps in some places and by dissolution-reprecipitation with variable amounts of recycling in other places. Our results demonstrate the complex effects that interaction with limited amounts of fluids can have on <sup>40</sup>Ar/<sup>39</sup>Ar dates of alkali feldspar and U-Pb dates of apatite and thereby reinforce previous critique of their suitability for thermochronological reconstructions. We further identify and discuss potential implications for noble gas geochronology of groundwaters and fission track dating of apatite.
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spelling doaj-art-d5f79acafa5d48ccbef409ee7b5c32452025-08-20T02:00:27ZengMDPI AGGeosciences2076-32632024-12-01141235810.3390/geosciences14120358Excess <sup>40</sup>Ar in Alkali Feldspar and <sup>206,207</sup>Pb in Apatite Caused by Fluid-Induced Recrystallisation in a Semi-Closed Environment in Proterozoic (Meta)Granites of the Mt Isa Inlier, NE AustraliaDaniil Popov0Richard Spikings1André Navin Paul2Maria Ovtcharova3Massimo Chiaradia4Martin Kutzschbach5Alexey Ulianov6Gary O’Sullivan7David Chew8Kalin Kouzmanov9Eszter Badenszki10J. Stephen Daly11Joshua H. F. L. Davies12CNRS, Université d’Orléans, CEMHTI UPR, 3079 Orléans, FranceDepartment of Earth Sciences, University of Geneva, 13 Rue des Maraichers, CH-1205 Geneva, SwitzerlandDepartment of Earth Sciences, University of Geneva, 13 Rue des Maraichers, CH-1205 Geneva, SwitzerlandDepartment of Earth Sciences, University of Geneva, 13 Rue des Maraichers, CH-1205 Geneva, SwitzerlandDepartment of Earth Sciences, University of Geneva, 13 Rue des Maraichers, CH-1205 Geneva, SwitzerlandGeology & Palaeoenvironmental Research, Goethe University Frankfurt, 60438 Frankfurt am Main, GermanyInstitute of Earth Sciences, University of Lausanne, UNIL-Mouline, CH-1015 Lausanne, SwitzerlandUCD School of Earth Sciences, University College Dublin, Dublin 4 Belfield, IrelandDepartment of Geology, School of Natural Sciences, Trinity College Dublin, Dublin 2 Dublin, IrelandDepartment of Earth Sciences, University of Geneva, 13 Rue des Maraichers, CH-1205 Geneva, SwitzerlandUCD School of Earth Sciences, University College Dublin, Dublin 4 Belfield, IrelandUCD School of Earth Sciences, University College Dublin, Dublin 4 Belfield, IrelandSciences de la Terre et de l’atmosphère/Geotop, Université du Québec à Montréal, Montréal, QC H2X 3Y7, CanadaInterpretation of <sup>40</sup>Ar/<sup>39</sup>Ar dates of alkali feldspar and U-Pb dates of apatite depends on the dominant mechanism of isotopic transport in these minerals, which can be either diffusion or fluid-assisted dissolution-reprecipitation. To clarify the contributions of these processes, we have conducted a holistic study of alkali feldspar, apatite and other minerals from the Mt. Isa Inlier in NE Australia. Mineral characterisation by electron microscopy, optical cathodoluminescence imaging and element mapping reveal a complex interplay of textures resulting from magmatic crystallisation, deuteric recrystallisation, local deformation with subsequent higher-temperature alteration, and finally ubiquitous low-temperature alteration. U-Pb and Pb isotopic data for zircon, apatite, fluorite and alkali feldspar suggest that the latter event occurred at ~300 Ma and was associated with fluid-assisted exchange of Pb isotopes between minerals in the same rock, causing some apatite grains to have <sup>207</sup>Pb-corrected U-Pb dates that exceed their crystallisation age. However, this event had no unequivocal effect on the <sup>40</sup>Ar/<sup>39</sup>Ar or Rb-Sr systematics of the alkali feldspar, which were disturbed by higher-temperature alteration at ~1450 Ma. The age of the latter event is derived from Rb-Sr data. <sup>40</sup>Ar/<sup>39</sup>Ar dates are very scattered and suggest that <sup>40</sup>Ar redistribution proceeded by diffusion in the presence of traps in some places and by dissolution-reprecipitation with variable amounts of recycling in other places. Our results demonstrate the complex effects that interaction with limited amounts of fluids can have on <sup>40</sup>Ar/<sup>39</sup>Ar dates of alkali feldspar and U-Pb dates of apatite and thereby reinforce previous critique of their suitability for thermochronological reconstructions. We further identify and discuss potential implications for noble gas geochronology of groundwaters and fission track dating of apatite.https://www.mdpi.com/2076-3263/14/12/358apatiteU-Pbalkali feldspar<sup>40</sup>Ar/<sup>39</sup>ArRb-Srgeochronology
spellingShingle Daniil Popov
Richard Spikings
André Navin Paul
Maria Ovtcharova
Massimo Chiaradia
Martin Kutzschbach
Alexey Ulianov
Gary O’Sullivan
David Chew
Kalin Kouzmanov
Eszter Badenszki
J. Stephen Daly
Joshua H. F. L. Davies
Excess <sup>40</sup>Ar in Alkali Feldspar and <sup>206,207</sup>Pb in Apatite Caused by Fluid-Induced Recrystallisation in a Semi-Closed Environment in Proterozoic (Meta)Granites of the Mt Isa Inlier, NE Australia
Geosciences
apatite
U-Pb
alkali feldspar
<sup>40</sup>Ar/<sup>39</sup>Ar
Rb-Sr
geochronology
title Excess <sup>40</sup>Ar in Alkali Feldspar and <sup>206,207</sup>Pb in Apatite Caused by Fluid-Induced Recrystallisation in a Semi-Closed Environment in Proterozoic (Meta)Granites of the Mt Isa Inlier, NE Australia
title_full Excess <sup>40</sup>Ar in Alkali Feldspar and <sup>206,207</sup>Pb in Apatite Caused by Fluid-Induced Recrystallisation in a Semi-Closed Environment in Proterozoic (Meta)Granites of the Mt Isa Inlier, NE Australia
title_fullStr Excess <sup>40</sup>Ar in Alkali Feldspar and <sup>206,207</sup>Pb in Apatite Caused by Fluid-Induced Recrystallisation in a Semi-Closed Environment in Proterozoic (Meta)Granites of the Mt Isa Inlier, NE Australia
title_full_unstemmed Excess <sup>40</sup>Ar in Alkali Feldspar and <sup>206,207</sup>Pb in Apatite Caused by Fluid-Induced Recrystallisation in a Semi-Closed Environment in Proterozoic (Meta)Granites of the Mt Isa Inlier, NE Australia
title_short Excess <sup>40</sup>Ar in Alkali Feldspar and <sup>206,207</sup>Pb in Apatite Caused by Fluid-Induced Recrystallisation in a Semi-Closed Environment in Proterozoic (Meta)Granites of the Mt Isa Inlier, NE Australia
title_sort excess sup 40 sup ar in alkali feldspar and sup 206 207 sup pb in apatite caused by fluid induced recrystallisation in a semi closed environment in proterozoic meta granites of the mt isa inlier ne australia
topic apatite
U-Pb
alkali feldspar
<sup>40</sup>Ar/<sup>39</sup>Ar
Rb-Sr
geochronology
url https://www.mdpi.com/2076-3263/14/12/358
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