A geomagnetic induction anomaly from IMS data near Hudson Bay, and its relation to crustal electrical conductivity in central North America

Abstract

Canadian geomagnetic data collected during the International Magnetospheric Study are used to investigate the terrestrial electrical conductivity structure of north-eastern Manitoba and part of the North-west Territories. The computed transfer functions resolve a major conductor trending east-west between the communities of Gillam and Back in Manitoba. Regional trends in the surface geology suggest that this conductor may be linked with the North American Central Plains electrical conductor. Twodimensional modelling of the data suggests that the conductor dips to the north from a small depth beneath Gillam and may extend to the lowermost C N S t .

The Longest Conductivity Anomaly in the World Explained: Sulphides in Fold Hinges Causing Very High Electrical Anisotropy

“…1). This anomaly, mostly in the deep crust, has been tracked from Wyoming through the Dakotas and Saskatchewan over to northern Manitoba (Alabi et al, 1975;Handa and Camfield, 1984;Gupta et al, 1985), and possibly has a counterpart in Scandinavia (Jones, 1993a). Camfield and Gough (1977), in an insightful paper, suggested that the conductivity anomaly is the geophysical marker for a Proterozoic collision zone from the southern Rockies to northern Canada-a proposal that conflicted with the then prevailing view that the Wyoming and Superior cratons were contiguous.…”

The COPROD2 Dataset: Tectonic Setting, Recorded MT Data, and Comparison of Models.

“…Data from an International Magnetospheric Study (IMS) chain of magnetometers running north-south alongside Hudson's Bay in Manitoba were shown to exhibit a strong reversal in ,H,, between two stations; BCK (Back: 57.7°N) and GIM (Gillam: 56.4°N) (GUPTA et al, 1985). These data were modelled two-dimensionally as a 25 SZ.m body at a depth of 5 km, of weaklyresolved thickness extent but with a definite northward dip.…”

Electromagnetic image of the Trans-Hudson orogen — THO94 transect

“…The GDS arrays and profiles that followed (Camfield et al 1970;Porath et al 1970Porath et al , 1971Gough and Camfield 1972;Alabi et al 1975;Handa and Camfield 1984;Gupta et al 1985) suggested that the NACP was morphologically linear and extended for some 2000 km, but that its origin was not fully known along its entire length. Later studies using the MT technique have shown that the anomaly is in the crust and has a geometry that can be spatially identified with specific domains of the internides of the THO.…”

“…At greater depths, an angle of 40°is more appropriate. In the location of the MT profile, the THO rotates to the northeast towards Hudson Bay (Hoffman 1989), as does the NACP anomaly (Gupta et al 1985). An MT strike angle of 60°confirms the eastward rotation of the crustal structures, while a deeper angle of 40°does the same for deeper structures in the upper lithospheric mantle.…”

“…(1) Association with graphite present in schistose rocks in a belt traced by Lidiak (1971), located within Precambrian basement rocks under the Great Plains (Camfield et al 1970;Gough and Camfield 1972;Handa and Camfield 1984); (2) Trapped saline water in fracture rocks (Handa and Camfield 1984); (3) Partial serpentinization of mafic and ultramafic oceanic rocks on the ridge crest of a preexistent oceanic crust (Gupta et al 1985;Green et al 1987); (4) Association with carbonated and metamorphosed slate rocks, deposited in foreland basins (Boerner et al 1996); and (5) Presence of sulphides in the fold hinges of the collision zone between the La Ronge volcanic arc and the internal zones of the Wyoming and Rae-Hearne Archean cratons (Jones et al , 2005. Detailed analysis of reflection data by Morel-à-l'Huisser et al (1990) was not conclusive in associating the low-velocity zones with the NACP, as located by Jones and Savage (1986).…”