Age significance of U-Th-Pb zircon data from early Archaean rocks of west Greenland - a reassessment based on combined ion-microprobe and imaging studies
The geochronological evolution of early Archaean Amitsoq gneisses from southern West Greenland is reassessed here using the well-established cathodoluminescence imaging method both to reveal previously undocumented complex zircon growth histories and to control positioning of ion-microprobe U-Th-Pb...
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ftqueensland:oai:eprints.qut.edu.au:126145 2024-04-28T08:21:36+00:00 Age significance of U-Th-Pb zircon data from early Archaean rocks of west Greenland - a reassessment based on combined ion-microprobe and imaging studies Whitehouse, M. J. Kamber, B. S. Moorbath, S. 1999 https://eprints.qut.edu.au/126145/ unknown Elsevier doi:10.1016/s0009-2541(99)00066-2 Whitehouse, M. J., Kamber, B. S., & Moorbath, S. (1999) Age significance of U-Th-Pb zircon data from early Archaean rocks of west Greenland - a reassessment based on combined ion-microprobe and imaging studies. Chemical Geology, 160(3), pp. 201-224. https://eprints.qut.edu.au/126145/ Science & Engineering Faculty; Australian Research Centre for Aerospace Automation Consult author(s) regarding copyright matters This work is covered by copyright. Unless the document is being made available under a Creative Commons Licence, you must assume that re-use is limited to personal use and that permission from the copyright owner must be obtained for all other uses. If the document is available under a Creative Commons License (or other specified license) then refer to the Licence for details of permitted re-use. It is a condition of access that users recognise and abide by the legal requirements associated with these rights. If you believe that this work infringes copyright please provide details by email to qut.copyright@qut.edu.au Chemical Geology Amitsoq gneiss absolute age (U-Pb) zircon ion probe cathodoluminescence Archaean crustal evolution lu-hf neodymium isotopes godthaab district amitsoq gneisses complex hafnium earth constraints Geochemistry & Geophysics Contribution to Journal 1999 ftqueensland https://doi.org/10.1016/s0009-2541(99)00066-2 2024-04-03T15:11:16Z The geochronological evolution of early Archaean Amitsoq gneisses from southern West Greenland is reassessed here using the well-established cathodoluminescence imaging method both to reveal previously undocumented complex zircon growth histories and to control positioning of ion-microprobe U-Th-Pb analyses. Several of the gneisses typically contain zircon grains with greater than or equal to 3.8 Ga cores of igneous origin, mostly completely mantled by growth banded magmatic zircon at ca. 3.65 Ga and in turn partly mantled by late Archaean metamorphic overgrowths at ca. 2.7 Ga. The greater than or equal to 3.8 Ga cores are regarded as inherited, with apparent dates ranging down to ca. 3.65 Ga reflecting differential Pb loss. This contrasts with published views interpreting greater than or equal to 3.8 Ga dates as emplacement ages of the host rock to the zircons, with all younger ages representing later Pb loss and/or metamorphic recrystallisation. Two of the analysed gneisses have discordant relationships to metasedimentary enclaves containing accessory apatite with graphite inclusions whose C-isotope ratios have been considered as biogenic in origin. The present data show that the minimum age of the enclaves is 3.65 Ga and not 3.85 Ga as previously claimed. This has important implications for the current debate on the possibility of temporal overlap of earliest life with a bolide impact scenario terminating at greater than or equal to 3.8 Ga (as on the moon). We also discuss the implication of the discovery of highly complex internal structures in Amitsoq gneiss zircons for the interpretation of published, zircon derived Lu-Hf information. (C) 1999 Elsevier Science B.V. All rights reserved. Article in Journal/Newspaper Greenland Queensland University of Technology: QUT ePrints Chemical Geology 160 3 201 224 |
institution |
Open Polar |
collection |
Queensland University of Technology: QUT ePrints |
op_collection_id |
ftqueensland |
language |
unknown |
topic |
Amitsoq gneiss absolute age (U-Pb) zircon ion probe cathodoluminescence Archaean crustal evolution lu-hf neodymium isotopes godthaab district amitsoq gneisses complex hafnium earth constraints Geochemistry & Geophysics |
spellingShingle |
Amitsoq gneiss absolute age (U-Pb) zircon ion probe cathodoluminescence Archaean crustal evolution lu-hf neodymium isotopes godthaab district amitsoq gneisses complex hafnium earth constraints Geochemistry & Geophysics Whitehouse, M. J. Kamber, B. S. Moorbath, S. Age significance of U-Th-Pb zircon data from early Archaean rocks of west Greenland - a reassessment based on combined ion-microprobe and imaging studies |
topic_facet |
Amitsoq gneiss absolute age (U-Pb) zircon ion probe cathodoluminescence Archaean crustal evolution lu-hf neodymium isotopes godthaab district amitsoq gneisses complex hafnium earth constraints Geochemistry & Geophysics |
description |
The geochronological evolution of early Archaean Amitsoq gneisses from southern West Greenland is reassessed here using the well-established cathodoluminescence imaging method both to reveal previously undocumented complex zircon growth histories and to control positioning of ion-microprobe U-Th-Pb analyses. Several of the gneisses typically contain zircon grains with greater than or equal to 3.8 Ga cores of igneous origin, mostly completely mantled by growth banded magmatic zircon at ca. 3.65 Ga and in turn partly mantled by late Archaean metamorphic overgrowths at ca. 2.7 Ga. The greater than or equal to 3.8 Ga cores are regarded as inherited, with apparent dates ranging down to ca. 3.65 Ga reflecting differential Pb loss. This contrasts with published views interpreting greater than or equal to 3.8 Ga dates as emplacement ages of the host rock to the zircons, with all younger ages representing later Pb loss and/or metamorphic recrystallisation. Two of the analysed gneisses have discordant relationships to metasedimentary enclaves containing accessory apatite with graphite inclusions whose C-isotope ratios have been considered as biogenic in origin. The present data show that the minimum age of the enclaves is 3.65 Ga and not 3.85 Ga as previously claimed. This has important implications for the current debate on the possibility of temporal overlap of earliest life with a bolide impact scenario terminating at greater than or equal to 3.8 Ga (as on the moon). We also discuss the implication of the discovery of highly complex internal structures in Amitsoq gneiss zircons for the interpretation of published, zircon derived Lu-Hf information. (C) 1999 Elsevier Science B.V. All rights reserved. |
format |
Article in Journal/Newspaper |
author |
Whitehouse, M. J. Kamber, B. S. Moorbath, S. |
author_facet |
Whitehouse, M. J. Kamber, B. S. Moorbath, S. |
author_sort |
Whitehouse, M. J. |
title |
Age significance of U-Th-Pb zircon data from early Archaean rocks of west Greenland - a reassessment based on combined ion-microprobe and imaging studies |
title_short |
Age significance of U-Th-Pb zircon data from early Archaean rocks of west Greenland - a reassessment based on combined ion-microprobe and imaging studies |
title_full |
Age significance of U-Th-Pb zircon data from early Archaean rocks of west Greenland - a reassessment based on combined ion-microprobe and imaging studies |
title_fullStr |
Age significance of U-Th-Pb zircon data from early Archaean rocks of west Greenland - a reassessment based on combined ion-microprobe and imaging studies |
title_full_unstemmed |
Age significance of U-Th-Pb zircon data from early Archaean rocks of west Greenland - a reassessment based on combined ion-microprobe and imaging studies |
title_sort |
age significance of u-th-pb zircon data from early archaean rocks of west greenland - a reassessment based on combined ion-microprobe and imaging studies |
publisher |
Elsevier |
publishDate |
1999 |
url |
https://eprints.qut.edu.au/126145/ |
genre |
Greenland |
genre_facet |
Greenland |
op_source |
Chemical Geology |
op_relation |
doi:10.1016/s0009-2541(99)00066-2 Whitehouse, M. J., Kamber, B. S., & Moorbath, S. (1999) Age significance of U-Th-Pb zircon data from early Archaean rocks of west Greenland - a reassessment based on combined ion-microprobe and imaging studies. Chemical Geology, 160(3), pp. 201-224. https://eprints.qut.edu.au/126145/ Science & Engineering Faculty; Australian Research Centre for Aerospace Automation |
op_rights |
Consult author(s) regarding copyright matters This work is covered by copyright. Unless the document is being made available under a Creative Commons Licence, you must assume that re-use is limited to personal use and that permission from the copyright owner must be obtained for all other uses. If the document is available under a Creative Commons License (or other specified license) then refer to the Licence for details of permitted re-use. It is a condition of access that users recognise and abide by the legal requirements associated with these rights. If you believe that this work infringes copyright please provide details by email to qut.copyright@qut.edu.au |
op_doi |
https://doi.org/10.1016/s0009-2541(99)00066-2 |
container_title |
Chemical Geology |
container_volume |
160 |
container_issue |
3 |
container_start_page |
201 |
op_container_end_page |
224 |
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1797583854273298432 |