CRUSTAL AFFINITY AND RELATIVE TIMING OF MAJOR TECTONIC EVENTS ON THE NORTH-EASTERN CANADIAN POLAR MARGIN

The north-eastern Canadian polar margin is bordered to the north by the Alpha Ridge, a dominantly magmatic complex within the Amerasia Basin of the Arctic Ocean. The characteristics of the gravity and magnetic fields change notably along the polar margin, with two main segments recognised. First, the Beaufort Sea NE to western Ellesmere Island segment is characterised by large magnitude elliptical gravity highs and magnetic lows. Second, the Ellesmere Island-Alpha Ridge segment of the margin is characterised by moderate gravity anomalies and irregularly distributed magnetic highs. The geophysical signature of the first segment is typical of passive continental margins. Aeromagnetic and gravity data in the transition zone between these contrasting domains of the Canadian polar margin have been analysed using various edge enhancement methods and the results highlight several magnetic domains as well as some known and a number of previously unknown tectonic and magmatic elements. Dykes and other structures have NW-SE, NE-SW and N-S major trends. Magnetic highs observed over the Alpha Ridge indicate the occurrence of extensive and voluminous crustal magmatic bodies. Combined 2-D gravity and magnetic data modelling along five profiles constrained by coincident deep seismic refraction velocity models implies the presence of a number of distinct crustal bodies and major sedimentary sub-basins. High density and highly magnetised crustal layers occur beneath the offshore regions. Moho depths vary from 26-29 km offshore to 25-32 km onshore. A continental affinity for all crustal units in the 2-D models is inferred. It is generally considered that sea-floor spreading in Canada Basin (the presumed oceanic part of the Amerasia Basin), Alpha Ridge magmatism and much of the associated widespread magmatic activity occurred in the Early Cretaceous. Absence of these volcanic and intrusive rocks in the imaged sub-basins beneath the northeastern Canadian polar margin area suggests that these sub-basins probably formed after the Alpha Ridge magmatism.