NEW SEISMIC, MAGNETIC, AND GRAVITY CONSTRAINTS ON THE CRUSTAL STRUCTURE OF THE LINCOLN SEA CONTINENT-OCEAN TRANSITION

A new seismic model of Canada's northeasternmost margin indicates a complex continent to ocean transition with similarities to both volcanic and nonvolcanic margins. The crustal structure beneath the Lincoln Sea includes: (i) a continental shelf with a uniform 3 km thick cover (velocity = 1.8-3.6 km/s) overlying at least 6 km of synrift(?) basinal strata (velocity = 4.3 -4.9 km/s) that terminate near the base of the slope; (ii) a thick unit of oceanic layer 2-type velocity (5.4-5.8 km/s) overlying a velocity structure resembling a volcanic margin; (iii) a high-velocity lower crust (> 7.4 km/s) resembling North Atlantic volcanic margins or the Alpha Ridge but different from the Lomonosov Ridge near the North Pole; (iv) a change in velocity structure 15-25 km seaward of the shelf-slope break that coincides with a distinct short-wavelength, high-amplitude magnetic anomaly and the centre of a steep gravity gradient; and (v) a suggested Moho depth of 23 km beneath the Lincoln Sea margin along 63 degrees W. The velocity structure beneath the Lincoln Sea is transitional from thinned continental crust beneath the shelf to a structure with oceanic affinities to the north. Typical, 10 km thick oceanic crust is not apparent beneath the northern Lincoln Sea. The upper crustal structure resembles a rifted, nonvolcanic margin such as the Goban Spur, while the high lower crustal velocity resembles a volcanic margin like the Hatton Bank or an oceanic complex like the Alpha Ridge. North of the seismic survey, the enigmatic Lincoln Sea plateau may be an intruded Lomonosov Ridge segment or a volcanic complex similar to the Alpha Ridge or the Morris Jesup Plateau.