Magnetic anisotropy and fabric of redbeds of the Great Slave Supergroup of Canada
The paper reports and interprets measurements of the anisotropy of magnetic susceptibility upon 254 oriented specimens from 82 stratigraphic horizons in redbeds of the Great Slave Supergroup exposed in the East Arm of Great Slave Lake, near the western edge of the Canadian Shield. These rocks lie be...
| Published in: | Geophysical Journal International |
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| Main Authors: | , , |
| Format: | Text |
| Language: | English |
| Published: |
Oxford University Press
1977
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| Subjects: | |
| Online Access: | http://gji.oxfordjournals.org/cgi/content/short/50/3/685 https://doi.org/10.1111/j.1365-246X.1977.tb01341.x |
| Summary: | The paper reports and interprets measurements of the anisotropy of magnetic susceptibility upon 254 oriented specimens from 82 stratigraphic horizons in redbeds of the Great Slave Supergroup exposed in the East Arm of Great Slave Lake, near the western edge of the Canadian Shield. These rocks lie between 1900 and 1700 Ma in age and have undergone only low-grade metamorphism. Ascending the stratigraphic column, the results refer to the Kahochella Group and to the Stark and Tochatwi Formations of the Christie Bay Group. Appropriate parameters of the principal susceptibilities indicate that the magnetic anisotropies of the Kahochella Group and Tochatwi Formation are related to the original sediment deposition with flow direction along the East Arm trend axis, i.e. north-east-south-west. The flow direction is in good agreement with estimates from cross-bedding by Hoffman, and with the triple junction failed-arm hypothesis of Burke & Dewey. Generally only gentle folding is present in the sampled parts of the Kahochella and Tochatwi rocks. In the intervening Stark Formation folding is much stronger with some isoclinal folds and steep dips. Here the magnetic anisotropy is shown to be dominated by tectonic strain, with magnetic lineations along the fold axis almost equal to magnetic foliations. A rotation of the Christie Bay area about a local vertical axis, proposed by Bingham & Evans as a possible explanation of palaeomagnetic results, is inconsistent with the magnetic lineations. As the dominant magnetic mineral in these redbeds is haematite, the relation of magnetic anisotropy to fabric in a haematite-bearing rock is examined. It is suggested that the observed relationships to depositional and deformational fabrics can be understood if the magnetic susceptibility is associated with the red coating on quartz grains. |
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