A revised Archaean chronology for the Napier Complex, Enderby Land, from SHRIMP ion-microprobe studies
The long and complex Archaean evolution of the Napier Complex of Enderby Land, characterized by high-grade metamorphism and several strong deformations, is reassessed in the light of new SHRIMPU–Pb zircon dating results bearing on the ages of protoliths and possible regional extents of distinct Arch...
Published in: | Antarctic Science |
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Language: | English |
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Cambridge University Press (CUP)
1997
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Online Access: | http://dx.doi.org/10.1017/s0954102097000102 https://www.cambridge.org/core/services/aop-cambridge-core/content/view/S0954102097000102 |
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crcambridgeupr:10.1017/s0954102097000102 2024-06-23T07:45:23+00:00 A revised Archaean chronology for the Napier Complex, Enderby Land, from SHRIMP ion-microprobe studies Harley, S.L. Black, L.P. 1997 http://dx.doi.org/10.1017/s0954102097000102 https://www.cambridge.org/core/services/aop-cambridge-core/content/view/S0954102097000102 en eng Cambridge University Press (CUP) https://www.cambridge.org/core/terms Antarctic Science volume 9, issue 1, page 74-91 ISSN 0954-1020 1365-2079 journal-article 1997 crcambridgeupr https://doi.org/10.1017/s0954102097000102 2024-05-29T08:09:52Z The long and complex Archaean evolution of the Napier Complex of Enderby Land, characterized by high-grade metamorphism and several strong deformations, is reassessed in the light of new SHRIMPU–Pb zircon dating results bearing on the ages of protoliths and possible regional extents of distinct Archaean tectonothermal events. Initial felsic igneous activity occurred over a significant time interval c . 3800 Ma ago. An age of 2980±9 Ma for the emplacement of charnockite at Proclamation Island might date the oldest tectonothermal event to be recognized in the Napier Complex. An ensuing, very-high grade, previously imprecisely dated tectonothermal event occurred at 2837±15 Ma. U–Pb zircon ages ranging from 2456+8/−5 Ma to 2481±4 Ma date a subsequent, protracted high-grade tectonothermal event. Whereas the ~2840 Ma event is of regional importance in the Amundsen Bay-Casey Bay area, it is possible that the ~2980 Ma event was of only moderate grade, minor importance, or even absent, in that part of the Complex. If so, the apparent trend to very-high temperature metamorphism in the Tula and Scott mountains compared with the Napier Mountains may reflect two distinct metamorphic events rather than a simple baric and thermal gradient. The oldest crustal component in the Napier Complex appears to have been of igneous derivation. Zircon populations in paragneisses at Mount Sones are similar to those in the nearby orthogneisses, which therefore may have been basement. Another paragneiss, in the Casey Bay area, yields no zircons older than 2840 Ma, probably indicating that pre-3000 Ma crust, which is now located nearby, was not exposed at the time of sedimentation there. The isotopic data are quite complex, particularly in rocks that experienced postcrystallization metamorphic temperatures of 1000°C or more. It is postulated that this complexity, which was largely the product of migration of radiogenic Pb within the zircon grains in ancient times, and produced local excesses of this element with respect to its parent U, was ... Article in Journal/Newspaper Amundsen Bay Antarctic Science Casey Bay Enderby Land Napier Mountains Proclamation Island Scott Mountains Cambridge University Press Tula ENVELOPE(-65.650,-65.650,-65.517,-65.517) Napier ENVELOPE(-58.440,-58.440,-62.167,-62.167) Amundsen Bay ENVELOPE(50.000,50.000,-66.917,-66.917) Proclamation Island ENVELOPE(53.683,53.683,-65.850,-65.850) Casey Bay ENVELOPE(48.000,48.000,-67.500,-67.500) Mount Sones ENVELOPE(51.483,51.483,-67.033,-67.033) Scott Mountains ENVELOPE(50.500,50.500,-67.500,-67.500) Napier Mountains ENVELOPE(53.667,53.667,-66.500,-66.500) Antarctic Science 9 1 74 91 |
institution |
Open Polar |
collection |
Cambridge University Press |
op_collection_id |
crcambridgeupr |
language |
English |
description |
The long and complex Archaean evolution of the Napier Complex of Enderby Land, characterized by high-grade metamorphism and several strong deformations, is reassessed in the light of new SHRIMPU–Pb zircon dating results bearing on the ages of protoliths and possible regional extents of distinct Archaean tectonothermal events. Initial felsic igneous activity occurred over a significant time interval c . 3800 Ma ago. An age of 2980±9 Ma for the emplacement of charnockite at Proclamation Island might date the oldest tectonothermal event to be recognized in the Napier Complex. An ensuing, very-high grade, previously imprecisely dated tectonothermal event occurred at 2837±15 Ma. U–Pb zircon ages ranging from 2456+8/−5 Ma to 2481±4 Ma date a subsequent, protracted high-grade tectonothermal event. Whereas the ~2840 Ma event is of regional importance in the Amundsen Bay-Casey Bay area, it is possible that the ~2980 Ma event was of only moderate grade, minor importance, or even absent, in that part of the Complex. If so, the apparent trend to very-high temperature metamorphism in the Tula and Scott mountains compared with the Napier Mountains may reflect two distinct metamorphic events rather than a simple baric and thermal gradient. The oldest crustal component in the Napier Complex appears to have been of igneous derivation. Zircon populations in paragneisses at Mount Sones are similar to those in the nearby orthogneisses, which therefore may have been basement. Another paragneiss, in the Casey Bay area, yields no zircons older than 2840 Ma, probably indicating that pre-3000 Ma crust, which is now located nearby, was not exposed at the time of sedimentation there. The isotopic data are quite complex, particularly in rocks that experienced postcrystallization metamorphic temperatures of 1000°C or more. It is postulated that this complexity, which was largely the product of migration of radiogenic Pb within the zircon grains in ancient times, and produced local excesses of this element with respect to its parent U, was ... |
format |
Article in Journal/Newspaper |
author |
Harley, S.L. Black, L.P. |
spellingShingle |
Harley, S.L. Black, L.P. A revised Archaean chronology for the Napier Complex, Enderby Land, from SHRIMP ion-microprobe studies |
author_facet |
Harley, S.L. Black, L.P. |
author_sort |
Harley, S.L. |
title |
A revised Archaean chronology for the Napier Complex, Enderby Land, from SHRIMP ion-microprobe studies |
title_short |
A revised Archaean chronology for the Napier Complex, Enderby Land, from SHRIMP ion-microprobe studies |
title_full |
A revised Archaean chronology for the Napier Complex, Enderby Land, from SHRIMP ion-microprobe studies |
title_fullStr |
A revised Archaean chronology for the Napier Complex, Enderby Land, from SHRIMP ion-microprobe studies |
title_full_unstemmed |
A revised Archaean chronology for the Napier Complex, Enderby Land, from SHRIMP ion-microprobe studies |
title_sort |
revised archaean chronology for the napier complex, enderby land, from shrimp ion-microprobe studies |
publisher |
Cambridge University Press (CUP) |
publishDate |
1997 |
url |
http://dx.doi.org/10.1017/s0954102097000102 https://www.cambridge.org/core/services/aop-cambridge-core/content/view/S0954102097000102 |
long_lat |
ENVELOPE(-65.650,-65.650,-65.517,-65.517) ENVELOPE(-58.440,-58.440,-62.167,-62.167) ENVELOPE(50.000,50.000,-66.917,-66.917) ENVELOPE(53.683,53.683,-65.850,-65.850) ENVELOPE(48.000,48.000,-67.500,-67.500) ENVELOPE(51.483,51.483,-67.033,-67.033) ENVELOPE(50.500,50.500,-67.500,-67.500) ENVELOPE(53.667,53.667,-66.500,-66.500) |
geographic |
Tula Napier Amundsen Bay Proclamation Island Casey Bay Mount Sones Scott Mountains Napier Mountains |
geographic_facet |
Tula Napier Amundsen Bay Proclamation Island Casey Bay Mount Sones Scott Mountains Napier Mountains |
genre |
Amundsen Bay Antarctic Science Casey Bay Enderby Land Napier Mountains Proclamation Island Scott Mountains |
genre_facet |
Amundsen Bay Antarctic Science Casey Bay Enderby Land Napier Mountains Proclamation Island Scott Mountains |
op_source |
Antarctic Science volume 9, issue 1, page 74-91 ISSN 0954-1020 1365-2079 |
op_rights |
https://www.cambridge.org/core/terms |
op_doi |
https://doi.org/10.1017/s0954102097000102 |
container_title |
Antarctic Science |
container_volume |
9 |
container_issue |
1 |
container_start_page |
74 |
op_container_end_page |
91 |
_version_ |
1802639539049594880 |