THE CANADIAN AEROMAGNETIC DATABASE - EVOLUTION AND APPLICATIONS TO THE DEFINITION OF MAJOR CRUSTAL BOUNDARIES

The Aeromagnetic Survey Programme of the Geological Survey of Canada, much of which was carried out under Federal-Provincial agreements, has resulted in over 10,000,000 line kilometres of data flown at a mean elevation of 305 m and a mean line separation of 800 m except in mountainous terrain where constant barometric altitudes were maintained for given areas. These data have been digitized (if not originally digitally recorded) and used to produce the 1:1,000,000 "Magnetic Anomaly Map Series" of the Geological Survey of Canada and associated gridded data. These grids were then combined with private data, shipborne data from the east and west coasts and U.S. Navy data from the high Arctic to produce the first all-digital version of the "Magnetic Anomaly Map of Canada". A study of the longer wavelength features on this anomaly map has resulted in greatly enhanced understanding of the major tectonic units and crustal boundaries within the Canadian landmass. Important features can be delineated by data enhancement and processing techniques such as upward continuation to emphasize deep sources, vertical gradients to sharply outline contacts (e.g. the boundaries of the economically important greenstone belts in the Canadian Shield), and shaded relief to highlight low-amplitude short-wavelength features. An additional technique which provides interesting insights is curvature analysis, which can be used to calculate the strike of an anomaly at each point. When plotted with a particular colour assigned according to the strike direction, the resulting patterns help to delineate trends over long distances.