Canadian Journal of Earth Sciences (Impact Factor: 1.34). 02/2011; 3(4):547-557. DOI: 10.1139/e66-039

ABSTRACT A regional aeromagnetic study of northern Manitoba suggests adjustments in the position of the Churchill–Superior boundary. This proposed boundary is correlated to a narrow, continuous magnetic low that changes direction at its northern end, from a northeast trend to an east–west trend that approximately parallels the 56° N. latitude line.The date pattern of age determinations chiefly supports the position of the proposed boundary. Comparison of aeromagnetic patterns to the geology establishes their close correlation. Aeromagnetic anomalies appear to be chiefly produced by near-surface material and can be correlated with the surface geology. A comparison of the gravity patterns to the aeromagnetic and geologic patterns establishes the apparent independence of the gravity patterns to the other two. The gravity anomalies appear to be produced by larger scale density contrasts which are not correlative with near-surface material. A deeper, crustal source of the gravity anomalies fits the evidence better.

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    ABSTRACT: Sutures have been identified or proposed at several sites in the Canadian Shield. Although many authors have suggested that some form of primitive plate tectonic processes have played a major role in the formation of the Archean crust of the Superior structural province, Proterozoic sutures, resembling Phanerozoic examples, have been proposed only within the younger Churchill and Grenville provinces, and at or near the boundaries between the older Superior and Slave provinces and the younger provinces. Gravity, magnetic, seismic and paleomagnetic data related to three proposed sutures in the latter category have been interpreted and generally support the view that the Shield comprises a mosaic of once separated, but now joined cratonic blocks. The sutures vary in complexity from wide zones, containing distinctive rocks formed at ancient accreting and consuming plate margins, to cryptic sutures marked only by abrupt changes in metamorphism and zones of cataclasis. Paired negative and positive gravity anomalies associated with these sutures have been interpreted in terms of juxtaposed crustal blocks of different density and thickness. Magnetic anomaly patterns change abruptly at structural province boundaries. Available seismic results support the concept of thickened crust in the younger province as derived from gravity modelling. Most authors prefer interpretation of Proterozoic pole positions in terms of one-plate models, but in some cases the interpretation of paleomagnetic data is equivocal and two-plate models have been proposed.
    Precambrian Research 03/1983; 19(4):349-384. DOI:10.1016/0301-9268(83)90021-9 · 6.02 Impact Factor
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    ABSTRACT: The aeromagnetic survey operations of the Geological Survey of Canada (GSC) began in 1946. utilizing a magnetometer in a bird system towed by a Royal Canadian Air Force Anson. Subsequent early operations were carried out by the GSC-operated Canso and Aero Commander aircraft. In 1961, the GSC in-house survey team formed the nucleus of a contract surveys group set up to monitor a new program established to complete the aeromagnetic mapping of the Canadian Shield in 12 years on a cost-sharing basis with the provinces. Today, surveys are carried out under contract by light twin-engine aircraft such as the Cessna 404 and even, in some cases, single-engine aircraft that utilize compact computer-controlled data acquisition and navigation systems and inboard magnetometer installations. Early systems were capable of resolution of only a few nanoteslas (nT) compared to the current standard of 0.1 nT or less, and flight path positioning with 35 mm film and photomosaics or topographical maps was extremely challenging. Despite these limitations, the careful selection of survey parameters and attention given to quality control have resulted in a world-class aeromagnetic data base that has contributed significantly to regional geological mapping and to mineral and oil exploration in Canada. Concurrently, the GSC carried out research programs into the development of instrumentation and into processing, interpretation, and enhancement techniques. In 1968, the GSC acquired its own platform, a Beechcraft B80 Queenair, which was used to develop high-sensitivity techniques, and an inboard gradiometer system, which was transferred to private industry in 1983. The GSC, in cooperation with the Flight Research Laboratory of the National Research Council of Canada, has also conducted a program of research into magnetometry and navigation combined with aeromagnetic studies of the Arctic since 1962.
    Canadian Journal of Earth Sciences 02/1993; 30(2):243-260. DOI:10.1139/e93-021 · 1.34 Impact Factor
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    ABSTRACT: A time-term analysis is made of the first arrival data from the 41 shots of the1965 Hudson Bay seismic experiment. An investigation of the water-wave data is made to determine which of three possible series of navigation is most consistent. A single-layered crust with a compressional wave velocity of 6.33 km/s and an upper mantle compressional wave velocity of 8.27 km/s are proposed for Hudson Bay. The Mohorovičić discontinuity is found to have considerable topography with depths ranging from 42.7 km to less than 26 km. The Churchill–Superior boundary is proposed to be a three-dimensional crustal feature and is extended offshore from Cape Smith and extended westward to the north of the Ottawa Islands through approximately 59° 40′ N and 82° 00′ W. The Mohorovičić discontinuity rises to depths of about 26 km beneath Chesterfield Inlet and Baker Lake. The mantle is about 40 km deep at Churchill, Manitoba and rises to about30 km some 130 km west of Gilmour Island, then drops to almost 42 km farther east. The sudden drop is related to the Churchill–Superior boundary.
    Canadian Journal of Earth Sciences 02/2011; 4(5):901-928. DOI:10.1139/e67-063 · 1.34 Impact Factor
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