Tectonic settings of continental crust formation: Insights from Pb isotopes in feldspar inclusions in zircon
International audience Most crustal rocks derive from preexisting crust, and so the composition of newly generated (juvenile) continental crust, and hence the tectonic settings of its formation, have remained difficult to determine, especially for the first billion years of Earth’s evolution. Modern...
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Online Access: | https://hal.archives-ouvertes.fr/hal-01718602 https://doi.org/10.1130/G38117.1 |
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ftunivnantes:oai:HAL:hal-01718602v1 2023-05-15T13:38:59+02:00 Tectonic settings of continental crust formation: Insights from Pb isotopes in feldspar inclusions in zircon Delavault, Helene Dhuime, Bruno Hawkesworth, Chris J. Cawood, Peter A. Marschall, Horst University of St Andrews Scotland Géosciences Montpellier Institut national des sciences de l'Univers (INSU - CNRS)-Université de Montpellier (UM)-Centre National de la Recherche Scientifique (CNRS)-Université des Antilles (UA) School of Earth Sciences Bristol University of Bristol Bristol Woods Hole Oceanographic Institution (WHOI) 2016-10 https://hal.archives-ouvertes.fr/hal-01718602 https://doi.org/10.1130/G38117.1 en eng HAL CCSD Geological Society of America info:eu-repo/semantics/altIdentifier/doi/10.1130/G38117.1 hal-01718602 https://hal.archives-ouvertes.fr/hal-01718602 doi:10.1130/G38117.1 ISSN: 0091-7613 EISSN: 0091-7613 Geology https://hal.archives-ouvertes.fr/hal-01718602 Geology, Geological Society of America, 2016, 44 (10), pp.819-822. ⟨10.1130/G38117.1⟩ [SDU.STU.GC]Sciences of the Universe [physics]/Earth Sciences/Geochemistry info:eu-repo/semantics/article Journal articles 2016 ftunivnantes https://doi.org/10.1130/G38117.1 2022-08-10T06:30:53Z International audience Most crustal rocks derive from preexisting crust, and so the composition of newly generated (juvenile) continental crust, and hence the tectonic settings of its formation, have remained difficult to determine, especially for the first billion years of Earth’s evolution. Modern primitive mantle–derived magmas have distinct U/Pb ratios, depending on whether they are generated in intraplate (mean U/Pb = 0.37) or in subduction settings (mean U/Pb = 0.10). The U/Pb ratio can therefore be used as a proxy for the tectonic settings in which juvenile continental crust is generated. This paper presents a new way to see back to the U/Pb ratios of juvenile continental crust that formed hundreds to thousands of millions of years ago, based on ion probe analysis of Pb isotopes in alkali feldspar and plagioclase inclusions within well-dated zircons. Pb isotope data are used to calculate the time-integrated U/Pb ratios (i.e., 238U/204Pb = µ) for the period between the Hf model age and the U-Pb crystallization age of the zircons. These time-integrated ratios reflect the composition of the juvenile continental crust at the time it was extracted from the mantle, and so they can be used as a proxy for the tectonic setting of formation of that crust. Two test samples with Proterozoic Hf model ages and Paleozoic crystallization ages have feldspar inclusions with measured Pb isotope ratios that overlap within analytical error for each sample. Sample Z7.3.1 from Antarctica has Pb isotope ratios (mean 206Pb/204Pb = 16.88 ± 0.08, 1σ) that indicate it was derived from source rocks with low U/Pb ratios (∼0.11), similar to those found in subduction-related settings. Sample Temora 2 from Australia has more radiogenic Pb isotope ratios (mean 206Pb/204Pb = 19.11 ± 0.23, 1σ) indicative of a source with higher U/Pb ratios (∼0.36), similar to magmas generated in intraplate settings. Analysis of detrital populations with a range of Hf model ages (e.g., Hadean to Phanerozoic), and for which zircons and their inclusions ... Article in Journal/Newspaper Antarc* Antarctica Université de Nantes: HAL-UNIV-NANTES Geology 44 10 819 822 |
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Université de Nantes: HAL-UNIV-NANTES |
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ftunivnantes |
language |
English |
topic |
[SDU.STU.GC]Sciences of the Universe [physics]/Earth Sciences/Geochemistry |
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[SDU.STU.GC]Sciences of the Universe [physics]/Earth Sciences/Geochemistry Delavault, Helene Dhuime, Bruno Hawkesworth, Chris J. Cawood, Peter A. Marschall, Horst Tectonic settings of continental crust formation: Insights from Pb isotopes in feldspar inclusions in zircon |
topic_facet |
[SDU.STU.GC]Sciences of the Universe [physics]/Earth Sciences/Geochemistry |
description |
International audience Most crustal rocks derive from preexisting crust, and so the composition of newly generated (juvenile) continental crust, and hence the tectonic settings of its formation, have remained difficult to determine, especially for the first billion years of Earth’s evolution. Modern primitive mantle–derived magmas have distinct U/Pb ratios, depending on whether they are generated in intraplate (mean U/Pb = 0.37) or in subduction settings (mean U/Pb = 0.10). The U/Pb ratio can therefore be used as a proxy for the tectonic settings in which juvenile continental crust is generated. This paper presents a new way to see back to the U/Pb ratios of juvenile continental crust that formed hundreds to thousands of millions of years ago, based on ion probe analysis of Pb isotopes in alkali feldspar and plagioclase inclusions within well-dated zircons. Pb isotope data are used to calculate the time-integrated U/Pb ratios (i.e., 238U/204Pb = µ) for the period between the Hf model age and the U-Pb crystallization age of the zircons. These time-integrated ratios reflect the composition of the juvenile continental crust at the time it was extracted from the mantle, and so they can be used as a proxy for the tectonic setting of formation of that crust. Two test samples with Proterozoic Hf model ages and Paleozoic crystallization ages have feldspar inclusions with measured Pb isotope ratios that overlap within analytical error for each sample. Sample Z7.3.1 from Antarctica has Pb isotope ratios (mean 206Pb/204Pb = 16.88 ± 0.08, 1σ) that indicate it was derived from source rocks with low U/Pb ratios (∼0.11), similar to those found in subduction-related settings. Sample Temora 2 from Australia has more radiogenic Pb isotope ratios (mean 206Pb/204Pb = 19.11 ± 0.23, 1σ) indicative of a source with higher U/Pb ratios (∼0.36), similar to magmas generated in intraplate settings. Analysis of detrital populations with a range of Hf model ages (e.g., Hadean to Phanerozoic), and for which zircons and their inclusions ... |
author2 |
University of St Andrews Scotland Géosciences Montpellier Institut national des sciences de l'Univers (INSU - CNRS)-Université de Montpellier (UM)-Centre National de la Recherche Scientifique (CNRS)-Université des Antilles (UA) School of Earth Sciences Bristol University of Bristol Bristol Woods Hole Oceanographic Institution (WHOI) |
format |
Article in Journal/Newspaper |
author |
Delavault, Helene Dhuime, Bruno Hawkesworth, Chris J. Cawood, Peter A. Marschall, Horst |
author_facet |
Delavault, Helene Dhuime, Bruno Hawkesworth, Chris J. Cawood, Peter A. Marschall, Horst |
author_sort |
Delavault, Helene |
title |
Tectonic settings of continental crust formation: Insights from Pb isotopes in feldspar inclusions in zircon |
title_short |
Tectonic settings of continental crust formation: Insights from Pb isotopes in feldspar inclusions in zircon |
title_full |
Tectonic settings of continental crust formation: Insights from Pb isotopes in feldspar inclusions in zircon |
title_fullStr |
Tectonic settings of continental crust formation: Insights from Pb isotopes in feldspar inclusions in zircon |
title_full_unstemmed |
Tectonic settings of continental crust formation: Insights from Pb isotopes in feldspar inclusions in zircon |
title_sort |
tectonic settings of continental crust formation: insights from pb isotopes in feldspar inclusions in zircon |
publisher |
HAL CCSD |
publishDate |
2016 |
url |
https://hal.archives-ouvertes.fr/hal-01718602 https://doi.org/10.1130/G38117.1 |
genre |
Antarc* Antarctica |
genre_facet |
Antarc* Antarctica |
op_source |
ISSN: 0091-7613 EISSN: 0091-7613 Geology https://hal.archives-ouvertes.fr/hal-01718602 Geology, Geological Society of America, 2016, 44 (10), pp.819-822. ⟨10.1130/G38117.1⟩ |
op_relation |
info:eu-repo/semantics/altIdentifier/doi/10.1130/G38117.1 hal-01718602 https://hal.archives-ouvertes.fr/hal-01718602 doi:10.1130/G38117.1 |
op_doi |
https://doi.org/10.1130/G38117.1 |
container_title |
Geology |
container_volume |
44 |
container_issue |
10 |
container_start_page |
819 |
op_container_end_page |
822 |
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1766113702416744448 |