Abstract
Recent work on prominent magnetic variation anomalies in Canada is reviewed. The first of these is on Ellesmere Island in the Arctic Archipelago, and results from magnetic and magnetotelluric data collected in 1967 are presented. Anomalous effects-i. e., an abnormally high level of magnetic activity coupled with a persistent tendency for the horizontal variation vector to be restricted to a single direction-appear to be confined to a narrow zone nearly 500km long stretching between Alert on the north coast and Eureka on the west. Recent data indicate that the strength of the anomaly is not uniform along its strike, but is somewhat diminished in the central and southern portions. The main features of the anomaly have been explained by postulating the presence of a long narrow conducting body located in the lower part of the crust. The existence of such a conductor would provide a natural channel for currents induced over a much broader area. It may also imply an abrupt upheaval of isotherms underneath Ellesmere Island. Available surface wave dispersion and heat flow information in the Ellesmere Island area will be discussed: the evidence supporting a thermal explanation for the geomagnetic anomaly is unconvincing, but still ambiguous.
The Mould Bay anomaly is located in the eastern part of the Arctic Archipelago and is known to extend over large portions of Prince Patrick and Melville Islands. Over this area shorter period fluctuations in the vertical component are very strongly attenuated. The presence of a massive conducting layer deep in the crust is postulated to explain the effect. Seismic, heat flow and gravity data are available in this area, but no clear relation to the geomagnetic anomaly has been found.
