Potential-field modeling of a Proterozoic half-graben near Blackwater Lake, Northwest Territories, Canada, and its implications for the Fort Simpson Magnetic Anomaly
A wedge of Proterozoic strata in the Blackwater Lake area of the Northwest Territories, Canada, is preserved below the sub-Cambrian unconformity in a half-graben associated with a large normal fault. Reflection seismic data define the shape of the wedge, but neither it nor drilling information is ad...
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crcansciencepubl:10.1139/e01-061 2023-12-17T10:30:18+01:00 Potential-field modeling of a Proterozoic half-graben near Blackwater Lake, Northwest Territories, Canada, and its implications for the Fort Simpson Magnetic Anomaly MacLean, B C Miles, W 2002 http://dx.doi.org/10.1139/e01-061 http://www.nrcresearchpress.com/doi/pdf/10.1139/e01-061 en eng Canadian Science Publishing http://www.nrcresearchpress.com/page/about/CorporateTextAndDataMining Canadian Journal of Earth Sciences volume 39, issue 2, page 169-187 ISSN 0008-4077 1480-3313 General Earth and Planetary Sciences journal-article 2002 crcansciencepubl https://doi.org/10.1139/e01-061 2023-11-19T13:38:26Z A wedge of Proterozoic strata in the Blackwater Lake area of the Northwest Territories, Canada, is preserved below the sub-Cambrian unconformity in a half-graben associated with a large normal fault. Reflection seismic data define the shape of the wedge, but neither it nor drilling information is adequate for identifying the strata preserved within the half-graben. Although these data permit either Tweed Lake Assemblage (density D = 2730-2780 kg/m 3 ) or MackenzieShaler Assemblage (D = 2580 kg/m 3 ) as the half-graben fill, gravity and (to a lesser extent) magnetic modeling show Tweed Lake Assemblage (~1270 Ma) to be the more likely candidate. Inclusion of any appreciable amount of MackenzieShaler Assemblage in the half-graben produces too low a gravity response and is therefore rejected. The character of the Fort Simpson Magnetic Anomaly (FSA) differs north and south of the Liard Line (~N61°). North of the line and south of Great Bear Lake, the FSA consists of a collection of strong, short-wavelength features superimposed on a weak, long-wavelength magnetic trend. Modeling of one of the higher amplitude, short-wavelength anomalies shows that the sources lies in the upper Proterozoic section immediately below the sub-Cambrian unconformity and therefore is not directly related to a basement terrane boundary. The weaker and longer wavelength component of the FSA may, however, mark a terrane boundary, as is commonly interpreted. Neither the shallow (short-wavelength) component nor the deep (long-wavelength) component has been sampled by drilling north of the Liard Line. Where the FSA crosses the track of the Liard Line, it undergoes a left-lateral offset. South of the Liard Line, the FSA is stronger with more distinct boundaries but lacks the overprint of shorter wavelength features. There, two drill holes have determined the source of the anomaly to be a shallow granite intrusion whose age has been established by UPb analysis as 1845 Ma. The number and magnitude of the differences in the FSA bring into question ... Article in Journal/Newspaper Fort Simpson Great Bear Lake Northwest Territories Canadian Science Publishing (via Crossref) Northwest Territories Canada Fort Simpson ENVELOPE(-121.320,-121.320,61.808,61.808) Great Bear Lake ENVELOPE(-120.753,-120.753,65.834,65.834) Liard ENVELOPE(-67.417,-67.417,-66.850,-66.850) Blackwater Lake ENVELOPE(-123.085,-123.085,64.000,64.000) Tweed Lake ENVELOPE(-125.885,-125.885,66.783,66.783) Canadian Journal of Earth Sciences 39 2 169 187 |
institution |
Open Polar |
collection |
Canadian Science Publishing (via Crossref) |
op_collection_id |
crcansciencepubl |
language |
English |
topic |
General Earth and Planetary Sciences |
spellingShingle |
General Earth and Planetary Sciences MacLean, B C Miles, W Potential-field modeling of a Proterozoic half-graben near Blackwater Lake, Northwest Territories, Canada, and its implications for the Fort Simpson Magnetic Anomaly |
topic_facet |
General Earth and Planetary Sciences |
description |
A wedge of Proterozoic strata in the Blackwater Lake area of the Northwest Territories, Canada, is preserved below the sub-Cambrian unconformity in a half-graben associated with a large normal fault. Reflection seismic data define the shape of the wedge, but neither it nor drilling information is adequate for identifying the strata preserved within the half-graben. Although these data permit either Tweed Lake Assemblage (density D = 2730-2780 kg/m 3 ) or MackenzieShaler Assemblage (D = 2580 kg/m 3 ) as the half-graben fill, gravity and (to a lesser extent) magnetic modeling show Tweed Lake Assemblage (~1270 Ma) to be the more likely candidate. Inclusion of any appreciable amount of MackenzieShaler Assemblage in the half-graben produces too low a gravity response and is therefore rejected. The character of the Fort Simpson Magnetic Anomaly (FSA) differs north and south of the Liard Line (~N61°). North of the line and south of Great Bear Lake, the FSA consists of a collection of strong, short-wavelength features superimposed on a weak, long-wavelength magnetic trend. Modeling of one of the higher amplitude, short-wavelength anomalies shows that the sources lies in the upper Proterozoic section immediately below the sub-Cambrian unconformity and therefore is not directly related to a basement terrane boundary. The weaker and longer wavelength component of the FSA may, however, mark a terrane boundary, as is commonly interpreted. Neither the shallow (short-wavelength) component nor the deep (long-wavelength) component has been sampled by drilling north of the Liard Line. Where the FSA crosses the track of the Liard Line, it undergoes a left-lateral offset. South of the Liard Line, the FSA is stronger with more distinct boundaries but lacks the overprint of shorter wavelength features. There, two drill holes have determined the source of the anomaly to be a shallow granite intrusion whose age has been established by UPb analysis as 1845 Ma. The number and magnitude of the differences in the FSA bring into question ... |
format |
Article in Journal/Newspaper |
author |
MacLean, B C Miles, W |
author_facet |
MacLean, B C Miles, W |
author_sort |
MacLean, B C |
title |
Potential-field modeling of a Proterozoic half-graben near Blackwater Lake, Northwest Territories, Canada, and its implications for the Fort Simpson Magnetic Anomaly |
title_short |
Potential-field modeling of a Proterozoic half-graben near Blackwater Lake, Northwest Territories, Canada, and its implications for the Fort Simpson Magnetic Anomaly |
title_full |
Potential-field modeling of a Proterozoic half-graben near Blackwater Lake, Northwest Territories, Canada, and its implications for the Fort Simpson Magnetic Anomaly |
title_fullStr |
Potential-field modeling of a Proterozoic half-graben near Blackwater Lake, Northwest Territories, Canada, and its implications for the Fort Simpson Magnetic Anomaly |
title_full_unstemmed |
Potential-field modeling of a Proterozoic half-graben near Blackwater Lake, Northwest Territories, Canada, and its implications for the Fort Simpson Magnetic Anomaly |
title_sort |
potential-field modeling of a proterozoic half-graben near blackwater lake, northwest territories, canada, and its implications for the fort simpson magnetic anomaly |
publisher |
Canadian Science Publishing |
publishDate |
2002 |
url |
http://dx.doi.org/10.1139/e01-061 http://www.nrcresearchpress.com/doi/pdf/10.1139/e01-061 |
long_lat |
ENVELOPE(-121.320,-121.320,61.808,61.808) ENVELOPE(-120.753,-120.753,65.834,65.834) ENVELOPE(-67.417,-67.417,-66.850,-66.850) ENVELOPE(-123.085,-123.085,64.000,64.000) ENVELOPE(-125.885,-125.885,66.783,66.783) |
geographic |
Northwest Territories Canada Fort Simpson Great Bear Lake Liard Blackwater Lake Tweed Lake |
geographic_facet |
Northwest Territories Canada Fort Simpson Great Bear Lake Liard Blackwater Lake Tweed Lake |
genre |
Fort Simpson Great Bear Lake Northwest Territories |
genre_facet |
Fort Simpson Great Bear Lake Northwest Territories |
op_source |
Canadian Journal of Earth Sciences volume 39, issue 2, page 169-187 ISSN 0008-4077 1480-3313 |
op_rights |
http://www.nrcresearchpress.com/page/about/CorporateTextAndDataMining |
op_doi |
https://doi.org/10.1139/e01-061 |
container_title |
Canadian Journal of Earth Sciences |
container_volume |
39 |
container_issue |
2 |
container_start_page |
169 |
op_container_end_page |
187 |
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1785583237508104192 |