Regional magnetic anomalies, magnetic units, and crustal structure in the Kenora District of Ontario

Abstract

Regional magnetic anomalies were smoothed from aeromagnetic maps in a part of the Superior Province of the Canadian Shield (latitudes 48°45′ to 50°00′ N; longitudes 93°30′ to 95°00′ W). It was found that anomaly lows lie over Keewatin greenstone belts, and highs over adjacent granitic areas.Surface mapping of magnetic susceptibility and NRM was combined with quantitative interpretation of the regional magnetic anomalies. It was found that, when considered regionally, magnetization lies primarily in the granitic bodies, with a continuous distribution from the surface down to the Intermediate (Conrad) discontinuity. Intensity of magnetization increases with depth, and is directed nearly along the direction of the present-day geomagnetic field.As an aid to the interpretation, a method of depth determination for deep crustal magnetic units with sloping sides is introduced, and one for variable intensity of magnetization with depth.