CHIME ages for granulites from the Napier Complex, East Antarctica
Th-U-bearmg minerals (monazite, zircon, xenotime and polycrase) in five granulite samples from Mt Riiser-Larsen (MA88022102), Beaver Island (2023B), Reference Peak (2306E and 2306J) and Mt Cronus (2275) in the western Napier Complex of East Antarctica were dated by CHIME on the basis of electron mic...
Main Authors: | , , , |
---|---|
Format: | Report |
Language: | English |
Published: |
Department of Earth Sciences, Faculty of Science, Okayama University
1998
|
Subjects: | |
Online Access: | https://nipr.repo.nii.ac.jp/?action=repository_uri&item_id=3027 http://id.nii.ac.jp/1291/00003027/ https://nipr.repo.nii.ac.jp/?action=repository_action_common_download&item_id=3027&item_no=1&attribute_id=18&file_no=1 |
id |
ftnipr:oai:nipr.repo.nii.ac.jp:00003027 |
---|---|
record_format |
openpolar |
spelling |
ftnipr:oai:nipr.repo.nii.ac.jp:00003027 2023-05-15T13:49:00+02:00 CHIME ages for granulites from the Napier Complex, East Antarctica Masao Asami Kazuhiro Suzuki Edward S. Grew Mamoru Adachi 1998-10 https://nipr.repo.nii.ac.jp/?action=repository_uri&item_id=3027 http://id.nii.ac.jp/1291/00003027/ https://nipr.repo.nii.ac.jp/?action=repository_action_common_download&item_id=3027&item_no=1&attribute_id=18&file_no=1 en eng Department of Earth Sciences, Faculty of Science, Okayama University Department of Earth and Planetary Sciences, Graduate School of Science, Nagoya University Department of Geological Sciences, University of Maine National Institute of Polar Research https://nipr.repo.nii.ac.jp/?action=repository_uri&item_id=3027 http://id.nii.ac.jp/1291/00003027/ AA1130866X Polar geoscience, 11, 172-199(1998-10) https://nipr.repo.nii.ac.jp/?action=repository_action_common_download&item_id=3027&item_no=1&attribute_id=18&file_no=1 CHIME dating 2500 Ma event ultra-high-temperature metamorphism Napier Complex Antarctica Departmental Bulletin Paper P(論文) 1998 ftnipr 2022-11-26T19:42:23Z Th-U-bearmg minerals (monazite, zircon, xenotime and polycrase) in five granulite samples from Mt Riiser-Larsen (MA88022102), Beaver Island (2023B), Reference Peak (2306E and 2306J) and Mt Cronus (2275) in the western Napier Complex of East Antarctica were dated by CHIME on the basis of electron microprobe ThO_2, UO_2 and PbO analyses Rocks from these localities, including some of the studied samples, are characterized by sapphirine-quartz-, orthopyroxene-sillimanite- and osurmlite-beanng mineral assemblages, indicating ultra-high-temperature granuhte-facies metamorphism A few grains of monazite in Sample MA88022102 and of zircon in Sample 2275 are chronologically heterogeneous, but other analyzed grains of monazite and zircon in these samples and all analyzed grains in the other samples, including xenotime, are almost homogeneous The core of a Mt Cronus zircon grain gives the oldest CHIME age, 3646±136 Ma, which could be a minimum age for protolith formation The homogeneous minerals, together with the older domains of Mt Riiser-Larsen zoned monazite and some grains of Mt Cronus zircon, give well-defined isochrons yielding consistent ages of 2404 Ma to 2441 Ma (within±54 Ma) on the ThO_2-PbO or UO_2-PbO plots Data points from zircon in Sample 2306J and from polycrase in Sample 2275 yield no isochron Given the petrographic characteristics of the samples and the high Pb-retentivity of the Th-U-bearmg minerals, we interpret the 2404-2441 Ma CHIME ages to date the ultra-high-temperature granulite-facies metamorphism The 2404-2441 Ma ages lie in the 2400-2500 Ma range of ages reported from numerous localities in the Napier Complex In the absence of decisive evidence for inherited older grains and of significant retrograde features in the analyzed samples, we consider that the Napier ultra-high-temperature metamorphism occurred not -2800 Ma ago as interpreted by most investigators, but 2400-2500 Ma ago Report Antarc* Antarctica East Antarctica Polar geoscience Beaver Island National Institute of Polar Research Repository, Japan East Antarctica Riiser-Larsen ENVELOPE(50.667,50.667,-66.783,-66.783) Napier ENVELOPE(-58.440,-58.440,-62.167,-62.167) Cronus ENVELOPE(-64.067,-64.067,-68.850,-68.850) Beaver Island ENVELOPE(50.867,50.867,-67.133,-67.133) Reference Peak ENVELOPE(50.483,50.483,-67.250,-67.250) |
institution |
Open Polar |
collection |
National Institute of Polar Research Repository, Japan |
op_collection_id |
ftnipr |
language |
English |
topic |
CHIME dating 2500 Ma event ultra-high-temperature metamorphism Napier Complex Antarctica |
spellingShingle |
CHIME dating 2500 Ma event ultra-high-temperature metamorphism Napier Complex Antarctica Masao Asami Kazuhiro Suzuki Edward S. Grew Mamoru Adachi CHIME ages for granulites from the Napier Complex, East Antarctica |
topic_facet |
CHIME dating 2500 Ma event ultra-high-temperature metamorphism Napier Complex Antarctica |
description |
Th-U-bearmg minerals (monazite, zircon, xenotime and polycrase) in five granulite samples from Mt Riiser-Larsen (MA88022102), Beaver Island (2023B), Reference Peak (2306E and 2306J) and Mt Cronus (2275) in the western Napier Complex of East Antarctica were dated by CHIME on the basis of electron microprobe ThO_2, UO_2 and PbO analyses Rocks from these localities, including some of the studied samples, are characterized by sapphirine-quartz-, orthopyroxene-sillimanite- and osurmlite-beanng mineral assemblages, indicating ultra-high-temperature granuhte-facies metamorphism A few grains of monazite in Sample MA88022102 and of zircon in Sample 2275 are chronologically heterogeneous, but other analyzed grains of monazite and zircon in these samples and all analyzed grains in the other samples, including xenotime, are almost homogeneous The core of a Mt Cronus zircon grain gives the oldest CHIME age, 3646±136 Ma, which could be a minimum age for protolith formation The homogeneous minerals, together with the older domains of Mt Riiser-Larsen zoned monazite and some grains of Mt Cronus zircon, give well-defined isochrons yielding consistent ages of 2404 Ma to 2441 Ma (within±54 Ma) on the ThO_2-PbO or UO_2-PbO plots Data points from zircon in Sample 2306J and from polycrase in Sample 2275 yield no isochron Given the petrographic characteristics of the samples and the high Pb-retentivity of the Th-U-bearmg minerals, we interpret the 2404-2441 Ma CHIME ages to date the ultra-high-temperature granulite-facies metamorphism The 2404-2441 Ma ages lie in the 2400-2500 Ma range of ages reported from numerous localities in the Napier Complex In the absence of decisive evidence for inherited older grains and of significant retrograde features in the analyzed samples, we consider that the Napier ultra-high-temperature metamorphism occurred not -2800 Ma ago as interpreted by most investigators, but 2400-2500 Ma ago |
format |
Report |
author |
Masao Asami Kazuhiro Suzuki Edward S. Grew Mamoru Adachi |
author_facet |
Masao Asami Kazuhiro Suzuki Edward S. Grew Mamoru Adachi |
author_sort |
Masao Asami |
title |
CHIME ages for granulites from the Napier Complex, East Antarctica |
title_short |
CHIME ages for granulites from the Napier Complex, East Antarctica |
title_full |
CHIME ages for granulites from the Napier Complex, East Antarctica |
title_fullStr |
CHIME ages for granulites from the Napier Complex, East Antarctica |
title_full_unstemmed |
CHIME ages for granulites from the Napier Complex, East Antarctica |
title_sort |
chime ages for granulites from the napier complex, east antarctica |
publisher |
Department of Earth Sciences, Faculty of Science, Okayama University |
publishDate |
1998 |
url |
https://nipr.repo.nii.ac.jp/?action=repository_uri&item_id=3027 http://id.nii.ac.jp/1291/00003027/ https://nipr.repo.nii.ac.jp/?action=repository_action_common_download&item_id=3027&item_no=1&attribute_id=18&file_no=1 |
long_lat |
ENVELOPE(50.667,50.667,-66.783,-66.783) ENVELOPE(-58.440,-58.440,-62.167,-62.167) ENVELOPE(-64.067,-64.067,-68.850,-68.850) ENVELOPE(50.867,50.867,-67.133,-67.133) ENVELOPE(50.483,50.483,-67.250,-67.250) |
geographic |
East Antarctica Riiser-Larsen Napier Cronus Beaver Island Reference Peak |
geographic_facet |
East Antarctica Riiser-Larsen Napier Cronus Beaver Island Reference Peak |
genre |
Antarc* Antarctica East Antarctica Polar geoscience Beaver Island |
genre_facet |
Antarc* Antarctica East Antarctica Polar geoscience Beaver Island |
op_relation |
https://nipr.repo.nii.ac.jp/?action=repository_uri&item_id=3027 http://id.nii.ac.jp/1291/00003027/ AA1130866X Polar geoscience, 11, 172-199(1998-10) https://nipr.repo.nii.ac.jp/?action=repository_action_common_download&item_id=3027&item_no=1&attribute_id=18&file_no=1 |
_version_ |
1766250336842940416 |