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TitleDefinition of magnetic domains within the Rae Craton, mainland Canadian Shield, Nunavut, Northwest Territories, Saskatchewan, and Alberta: their magnetic signatures and relationship to geology
AuthorThomas, M D
SourceGeological Survey of Canada, Open File 8343, 2018, 100 pages, (Open Access)
PublisherNatural Resources Canada
Documentopen file
Mediaon-line; digital
File formatpdf
ProvinceNunavut; Northwest Territories; Saskatchewan; Alberta
NTS45P; 46; 47A; 47B; 47C; 47D; 47E; 47F; 55; 56; 57A; 57B; 57C; 57D; 57E; 57F; 64I; 64P; 65; 66; 67A; 67B; 67C; 67D; 67E; 74I; 74J; 74K; 74L; 74M; 74N; 74O; 74P; 75; 76; 84I; 84P; 85A; 85H
Lat/Long WENS-113.0000 -80.0000 71.0000 58.0000
Subjectsgeophysics; structural geology; stratigraphy; geophysical interpretations; geophysical interpretations; magnetic interpretations; geophysical surveys; magnetic surveys; aeromagnetic surveys; magnetic anomalies; total field magnetics; structural domains; trend surface analyses; structural features; fault zones; faults; shear zones; intrusions; bedrock geology; lithology; metamorphic rocks; gneisses; granitic rocks; sedimentary rocks; iron formations; igneous rocks; intrusive rocks; crustal evolution; tectonic evolution; accretion; Archean; Canadian Shield; Churchill Province; Rae Craton; Arrowsmith Orogen; Chesterfield Block; MacQuoid Orogeny; Thelon Basin; Manchester Lake-Howard Lake Shear Zone; Black Bay Fault Zone; Amer Shear Zone; Wager Bay Shear Zone; Snowbird Tectonic Zone; Tyrell Shear Zone; Thelon Tectonic Zone; Talston Magmatic Zone; McDonald Fault; Athabasca Basin; Aberdeen Subbasin; Black-Bompas Fault Zone; Chesterfield Fault Zone; Chantrey Fault Zone; Grease River Shear Zone; Quoich River Fault; Tulemalu Fault; Big Lake Shear Zone; Hanbury Island Shear Zone; Pyke Fault Zone; geological mapping; Precambrian
Illustrationsgeoscientific sketch maps; index maps
ProgramSouth Rae Province Bedrock/Surficial geology, GEM2: Geo-mapping for Energy and Minerals
Released2018 03 06
AbstractThe Archean Rae craton, western Churchill Province, occupies a huge area within the northwestern mainland Canadian Shield. It extends >1600 km from the Talston magmatic zone northeastward to the east coast of Melville Peninsula, ranging in width from roughly 300 km to 900 km. The craton is covered by aeromagnetic data collected over many decades by Canada's National Aeromagnetic Survey Program, typically along lines 805 m apart at a flight elevation of 305 m. Additionally, many higher resolution aeromagnetic surveys have been completed during the last decade or so. The craton is geologically mapped at various scales, but most geological coverage is at a relatively large scale. For this reason magnetic data provided by the national program are considered to be of sufficient resolution to investigate relationships with geology.
Here, seventy-five magnetic domains are defined using textures, fabrics, patterns, orientations and intensities of residual total magnetic field anomalies and their derivative equivalents (first vertical derivative, tilt angle). Given that patterns and orientations of narrow derivative magnetic anomalies reflect closely geological structure, the magnetic domains can be viewed essentially as representative of structural domains. The maximum dimension of most domains is >100 km, but many attain dimensions of several 100 km. Although the Rae craton has an overall northeastward trend, a strong pattern of linear magnetic domains running parallel to this trend along the length of the craton is not apparent. A few generally relatively broad and parallel domains do run northeastward along the spine of the craton between roughly the Talston magmatic zone and Aberdeen sub-basin. Several narrower and typically less extensive domains also trend northeast within the Chesterfield block along the southeast margin of the craton southeast of the sub-basin. Where the southern part of the craton, south of the roughly east- trending Amer and Wager Bay shear zones, swings into a more eastward trend, linearity is lost and domains become smaller and more irregular in shape, with some trending across the craton.
The best developed linear pattern of domains probably lies between the Thelon magmatic zone and Chantrey fault zone, where several narrow to moderately wide, sub-parallel domains extend between the McDonald fault (and its northeastward projection) and Queen Maud Gulf. Eastward they change orientation progressively from northward to roughly N30°E towards the fault zone. A sense of a linear arrangement of domains is observed also on the Boothia and Melville peninsulas, with trends varying between approximately east-northeast and northeast. A broad area east of the Chantrey fault zone, north of the Amer and Wager Bay shear zones, south of the Boothia Peninsula and including the southern part of the Melville Peninsula contains some linear domains trending approximately northeast, but there are also sizable domains of irregular shape lacking an internal magnetic fabric characterized by prominent northeast trends.
Many close correlations between magnetic anomalies and mapped lithological units exist, but there are numerous examples where anomalies transect unit boundaries thus questioning boundary positions. Magnetic anomalies indicate probable lithological/compositional changes within many large gneissic units pointing to a need for more detailed mapping. Many examples of exceptionally strong magnetic highs are associated with mapped iron formations. Such highs in areas apparently lacking iron formations signify their potential presence. Magnetic patterns and signatures outline locations of small circular to roughly oval, unmapped igneous intrusions, and many faults not displayed on geological maps.
Summary(Plain Language Summary, not published)
Magnetic maps of the Precambrian Rae craton in the northwestern portion of the mainland Canadian Shield are used to define magnetic domains. The principal magnetic maps were of the residual total magnetic field and the first vertical derivative and tilt angle of the field. The latter two maps provide images that reflect very closely geological structure, hence magnetic domains essentially portray structural domains. At the craton scale, the definition of the domains provides a different perspective for evaluating structural relationships and tectonic development. At more local scales relationships between magnetic signatures and mapped geology sometimes support mapping, and in other cases call into question the attribution of a certain rock-type or positioning of a contact. The magnetic maps also indicate areas designated as single unit that are obviously much more complex, and this is to be expected given that geological mapping in many areas is largely reconnaissance in nature.