Paleomagnetism of Archean rocks from northwestern Ontario: Wabigoon gabbro, Wabigoon Subprovince
The Wabigoon gabbro of the Archean Wabigoon greenstone belt in northwestern Ontario preserves a univectorial natural remanent magnetization (NRM) with D = 246°, I = 12° (k = 19.5, α 95 = 10.5°, N = 11 sites). The precision is reduced if sample means are averaged, however (k = 9.3, α 95 = 9.2°, N = 2...
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1983
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Online Access: | http://dx.doi.org/10.1139/e83-172 http://www.nrcresearchpress.com/doi/pdf/10.1139/e83-172 |
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crcansciencepubl:10.1139/e83-172 2023-12-17T10:30:27+01:00 Paleomagnetism of Archean rocks from northwestern Ontario: Wabigoon gabbro, Wabigoon Subprovince Dunlop, David J. 1983 http://dx.doi.org/10.1139/e83-172 http://www.nrcresearchpress.com/doi/pdf/10.1139/e83-172 en eng Canadian Science Publishing http://www.nrcresearchpress.com/page/about/CorporateTextAndDataMining Canadian Journal of Earth Sciences volume 20, issue 12, page 1805-1817 ISSN 0008-4077 1480-3313 General Earth and Planetary Sciences journal-article 1983 crcansciencepubl https://doi.org/10.1139/e83-172 2023-11-19T13:38:17Z The Wabigoon gabbro of the Archean Wabigoon greenstone belt in northwestern Ontario preserves a univectorial natural remanent magnetization (NRM) with D = 246°, I = 12° (k = 19.5, α 95 = 10.5°, N = 11 sites). The precision is reduced if sample means are averaged, however (k = 9.3, α 95 = 9.2°, N = 29 samples). The paleomagnetic pole falls either at 160°W, 11°S (δp = 5.3°, δm = 10.6°), corresponding to an age of ~1300 Ma on the Laurentian apparent polar wander path, or the reverse of this, 20°E, 11° N, corresponding to a late Archean age (~2800 Ma). No ~1300 Ma igneous or metamorphic event is known in the area; a major west-northwest-trending dike about 9 km south of the gabbro yields a virtual geomagnetic pole at 122°W, 45°N and seems to be of Abitibi age (~2150 Ma) rather than Mackenzie age (~1250 Ma). A few gabbro samples and some greenstones from the intrusive baked zone have hybrid remanences in which a higher blocking temperature Kenoran-age (~2600 Ma) NRM is superimposed on the gabbro characteristic NRM. However, the Kenoran component may be a younger chemical remanent magnetization (CRM) residing in hematite. The hypothesis that the gabbro characteristic remanence is itself a hybrid of Kenoran and Keweenawan (~1100 Ma) NRM's, which would explain both the high between-sample scatter and the lack of a ~1300 Ma remagnetizing event, is considered but rejected because fewer than 10% of the gabbro samples exhibit multivectorial swings during alternating field or thermal cleaning. Two geomagnetic field reversals are recorded at interior sites, but only one or none is recorded near the margin of the intrusion. The different cooling histories of margin and interior, as well as the bulk of the other evidence, favour magnetization during initial cooling in late Archean time. Article in Journal/Newspaper Geomagnetic Pole Canadian Science Publishing (via Crossref) Canadian Journal of Earth Sciences 20 12 1805 1817 |
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Open Polar |
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Canadian Science Publishing (via Crossref) |
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crcansciencepubl |
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English |
topic |
General Earth and Planetary Sciences |
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General Earth and Planetary Sciences Dunlop, David J. Paleomagnetism of Archean rocks from northwestern Ontario: Wabigoon gabbro, Wabigoon Subprovince |
topic_facet |
General Earth and Planetary Sciences |
description |
The Wabigoon gabbro of the Archean Wabigoon greenstone belt in northwestern Ontario preserves a univectorial natural remanent magnetization (NRM) with D = 246°, I = 12° (k = 19.5, α 95 = 10.5°, N = 11 sites). The precision is reduced if sample means are averaged, however (k = 9.3, α 95 = 9.2°, N = 29 samples). The paleomagnetic pole falls either at 160°W, 11°S (δp = 5.3°, δm = 10.6°), corresponding to an age of ~1300 Ma on the Laurentian apparent polar wander path, or the reverse of this, 20°E, 11° N, corresponding to a late Archean age (~2800 Ma). No ~1300 Ma igneous or metamorphic event is known in the area; a major west-northwest-trending dike about 9 km south of the gabbro yields a virtual geomagnetic pole at 122°W, 45°N and seems to be of Abitibi age (~2150 Ma) rather than Mackenzie age (~1250 Ma). A few gabbro samples and some greenstones from the intrusive baked zone have hybrid remanences in which a higher blocking temperature Kenoran-age (~2600 Ma) NRM is superimposed on the gabbro characteristic NRM. However, the Kenoran component may be a younger chemical remanent magnetization (CRM) residing in hematite. The hypothesis that the gabbro characteristic remanence is itself a hybrid of Kenoran and Keweenawan (~1100 Ma) NRM's, which would explain both the high between-sample scatter and the lack of a ~1300 Ma remagnetizing event, is considered but rejected because fewer than 10% of the gabbro samples exhibit multivectorial swings during alternating field or thermal cleaning. Two geomagnetic field reversals are recorded at interior sites, but only one or none is recorded near the margin of the intrusion. The different cooling histories of margin and interior, as well as the bulk of the other evidence, favour magnetization during initial cooling in late Archean time. |
format |
Article in Journal/Newspaper |
author |
Dunlop, David J. |
author_facet |
Dunlop, David J. |
author_sort |
Dunlop, David J. |
title |
Paleomagnetism of Archean rocks from northwestern Ontario: Wabigoon gabbro, Wabigoon Subprovince |
title_short |
Paleomagnetism of Archean rocks from northwestern Ontario: Wabigoon gabbro, Wabigoon Subprovince |
title_full |
Paleomagnetism of Archean rocks from northwestern Ontario: Wabigoon gabbro, Wabigoon Subprovince |
title_fullStr |
Paleomagnetism of Archean rocks from northwestern Ontario: Wabigoon gabbro, Wabigoon Subprovince |
title_full_unstemmed |
Paleomagnetism of Archean rocks from northwestern Ontario: Wabigoon gabbro, Wabigoon Subprovince |
title_sort |
paleomagnetism of archean rocks from northwestern ontario: wabigoon gabbro, wabigoon subprovince |
publisher |
Canadian Science Publishing |
publishDate |
1983 |
url |
http://dx.doi.org/10.1139/e83-172 http://www.nrcresearchpress.com/doi/pdf/10.1139/e83-172 |
genre |
Geomagnetic Pole |
genre_facet |
Geomagnetic Pole |
op_source |
Canadian Journal of Earth Sciences volume 20, issue 12, page 1805-1817 ISSN 0008-4077 1480-3313 |
op_rights |
http://www.nrcresearchpress.com/page/about/CorporateTextAndDataMining |
op_doi |
https://doi.org/10.1139/e83-172 |
container_title |
Canadian Journal of Earth Sciences |
container_volume |
20 |
container_issue |
12 |
container_start_page |
1805 |
op_container_end_page |
1817 |
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1785583418727202816 |