Crustal structure across the Canadian High Arctic region from teleseismic receiver function analysis

Abstract

SUMMARY Results from an investigation of the crustal structure beneath the Canadian High Arctic and western Greenland are presented, using teleseismic data recorded by a network of 12 threecomponent broad-band seismograph stations deployed across the region. Of these stations, eight were deployed in summer 2000, in order to improve the spatial density of seismographs in this tectonically active but little studied region, in order to provide more information on the patterns of seismicity and the structure of the area. The typical station separation is of the order of 400‐600 km, a substantial improvement on the previous >1000 km spacing afforded by the permanent broad-band network. Teleseismic receiver functions are used to model the shear wave velocity structure of the crust beneath the stations, using both 1-D and 3-D analysis techniques. The velocity‐depth models show significant variation in the thickness and nature of the crust across the region. In the south and east, where the seismic stations lie on the Canadian Shield, the crustal structure is relatively simple, with Moho depths ranging from 35 km on the Boothia Peninsula to 45 km beneath southern Baffin Island. Further to the north and west, where the lithosphere has been deformed by orogenic events and basin formation, the patterns of azimuthal variation in the radial and tangential receiver functions suggest 3-D structure throughout the crust. The Moho depths around the margins of the Sverdrup Basin lie in the range 33‐37 km. At Mould Bay, on the western margin of the basin, a 5 km thick low-velocity layer overlies the main crustal sequence. The base of this layer can be modelled as a planar dipping structure with a southeasterly strike. The thinnest crust (27‐32 km) is modelled at Alert, on the northern coast of Ellesmere Island. In the southwest of the Arctic archipelago, tangential receiver functions at Holman show a pattern consistent with crustal anisotropy. The Moho depth in the region is undetermined; a layer of intermediate shear wave velocity, consistent with mafic lower-crustal material, is modelled at depths of 35‐55 km. The region around Holman lies at the focal point of the Mackenzie dyke swarm, believed to result from plume activity; therefore the intermediate-velocity layer may result from mafic underplating caused by the presence of the Mackenzie plume.