Crustal structure of the central Sverdrup Basin

Abstract

A synthesis of refraction data recorded in 1972 and 1973 in the central Sverdrup Basin with other geophysical data shows major features which correlate well with the regional geological structure. The record sections from the Arctic Archipelago show little coherent secondary energy compared with those from other areas of Canada. Normalization of the sections to remove effects of varying shot size and instrument gain has revealed a significant loss of amplitude and coherence of the upper and mid-crustal phases of the seismic energy on traversing a major northeast-trending structure between Melville and Lougheed Islands. The upper mantle phase (Pn), however, is not abnormally attenuated in its travel beneath the area. The aeromagnetic data reveal a major series of dykes or minor graben, a likely cause of scattering and attenuation of the seismic energy travelling within the crust. These seismic effects and the focal depths of earthquakes suggest that lateral heterogeneities in the crust may extend to near-mantle depths in this area. The age dates available suggest fracture or dyke development progressed from south to north beginning in the Early Cretaceous. The correlation of the recorded seismicity with these structures provides one of the better examples of an active, intraplate tectonic feature.East of King Christian Island (KCI) the refraction results concur with gravity and regional geology in suggesting a major change in crustal and upper mantle structure. Models derived using ray theory indicate a crust which thins from near 40 km beneath the eastern Sabine Peninsula to 32 km west of KCI. East of KCI the Moho may lie at 40 km beneath a complex crustal structure. The average crustal compressional wave velocity is between 5.9 and 6.4 km s−1 and the mean upper mantle velocity is 8.2 km s−1. The present study does not support the existence of a distinct mid-crustal layer with a velocity of about 7.3 km s−1.