Magnetic anomalies and the evolution of the Arctic

Extensive magnetic surveys have been made over the Arctic Ocean during the past 30 years, but it is very difficult to interrelate data sets, and even conclusions, from different surveys. Many uncertainties present in the data sets preclude a full compilation of the data in a single format at this time. This paper summarizes the information available and discusses the various interpretations made from the data sets. The many ambiguities in interpretation result in considerable uncertainties regarding present Arctic Basin structure, and therefore its evolution. Magnetic anomaly data over the Eurasia Basin have indicated possible spreading rates, however, and an analysis of Earth Physics Branch high-level airborne magnetic data over the Greenland end of the Nansen-Gakkel Ridge suggests rates of 8 mm/a from 0 to 3 Ma and S mm/a from 3 to 20 Ma. There is no persistent anomaly pattern associated with the Lomonosov Ridge, the evidence suggesting that the Ridge is of continental character. The magnetic pattern over the Alpha and Mendeleev Ridges is quite different from that over the Nansen-Gakkel Ridge. The amplitudes and character of the anomalies over the Alpha Ridge are similar in some respects to continental shield anomalies. A strongly positive, very long wavelength anomaly characterizes the Alpha Ridge, whereas the Nansen-Gakkel and most active spreading ridges have associated weak positive or negative very long wavelength anomalies. On the other hand, the magnetic pattern of the Alpha Ridge might be a result of a series of imbricate subduction zones and associated island arcs. Although many thousands of line-kilometres of magnetic survey data exist, the general understanding of the magnetic anomalies and their significance is still at a rudimentary level.