CIRCUM-CANADA BASIN CRUSTAL STRUCTURE MODELING: RIFTING STYLES AND VOLCANIC-NONVOLCANIC MARGIN SEGMENTATION

We have constructed 2-D gravity and magnetic models for several cross-sections of the Canadian and Alaska margins, Chukchi Plateau, and Alpha Ridge to investigate the geometry and structure of the different margins and the extent of volcanism during margin development. The locations of the transects were chosen to integrate published reflection and refraction seismic interpretations with new seismic reflection and sonobuoy refraction data collected during collaborative Canadian/American marine surveys. Bathymetric, gravity and magnetic values for the models were extracted from public-domain data compilations. Sonobuoy data analysis provided velocity information for the sedimentary column and upper crustal layers. The velocity results were used to depth-convert the seismic reflection data and provide geometric constraints for the crustal layers. Sonobuoy velocities were also used to constrain density values for the models using the Ludwig et al. (1970) velocity-density relationship curve, which is consistent with published velocity-density measurements of basalt and serpentinite samples from several IODP drill cores and new dredge sample analysis from the Chukchi Plateau and Nautilus Spur. Magnetization values used in the models are based on analogy to the inferred lithologies.

Models of the Alaskan and western Canadian Arctic rift margins show abrupt crustal necking. Most of Canada Basin is underlain by thin (6 to 8 km) highly attenuated continental crust or “transition” crust. Oceanic crust is restricted to a narrow central portion of the basin. Although syn-rift volcanoclastic layers are broadly distributed over southern Canada Basin, the region is interpreted to be non-volcanic. The southern limit of the Alpha Ridge HALIP extends beneath the deep sedimentary succession of Canada Basin. Moho depths beneath the Alpha Ridge are considerably deeper (25 to 30 km) than Canada Basin (18 to 22 km) and the thick crust is modeled as a uniform medium velocity(density) unit rather than a high velocity underplated layer beneath thinned continental crust. The volcanics associated with the Alpha Ridge HALIP extend onto the Canadian margin east of Sever Spur and along eastern edge of Chukchi Plateau. The southern boundary of the HALIP is complex, with large basement ridges and graben structures.