Analysis of geomagnetic variations in western British Columbia

Geomagnetic variation anomalies in the western structural province of the Canadian Cordillera are examined. Data were collected at five temporary geomagnetic observatories and analysed using single Station transfer functions, induction ellipses, and I-ratios. These data and the single station transfer functions from Cochrane and Hyndman (1970) and Dragert (1973) were interpreted. Geological and geophysical evidence suggest a different tectonic history for the northern and southern parts of British Columbia. The geomagnetic variations provide further evidence for this difference. Analog and numerical model studies indicate that several major features are causing the geomagnetic variations in the region. First there is a strong coast effect caused by the ocean-land conductivity contrast. The model studies show that an explanation of the observed coast effect requires a zone of high conductivity close to the surface and lying beneath both the ocean and the land. Second there is a strong correlation between the magnitude and direction of the inland induction arrows and the general structural trend. It is concluded that these inland induction arrows are caused by induced currents flowing along the structural province boundaries, possibly at the Mohorovicic discontinuity which has considerable variation in depth from province to province. Third, the offset of the induction arrows from a simple orientation perpendicular to the general structure suggests the presence of three east-west conductors. The major one is the Souther (1970) volcanic zone through the central region analysed. The other two are the edge of the North American craton south of Cache Creek and a proposed crustal discontinuity north, of the Prince Rupert - Prince George profile. This interpretation is consistent with the known geological and geophysical information regarding the tectonic history of British Columbia.Science, Faculty ofEarth, Ocean and Atmospheric Sciences, Department ofGraduat