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New Aerogeophysical Evidence for the Rotational Opening of
the Southern Canada Basin John M Brozena 1 (202-404-4346; john.brozena@nrl.navy.mil) Vicki A Childers 1 (202-404-1110; vicki@qur.nrl.navy.mil) Louis C Kovacs 1 (202-767-3013; skip@qur.nrl.navy.mil) Lawrence A Lawver 2 (512-471-0433; lawver@utig.ig.utexas.edu) 1Naval Research Laboratory , Code 7420 4555 Overlook Ave., SW, Washington, DC 20375-5350, United States 2University of Texas Institute for Geophysics, 4412 Spicewood Springs Rd. #600, Austin, TX 78759-8500, United States Historical aeromagnetic data and the reprocessed ERS-1 gravity data suggest the existence of an extinct spreading axis bisecting the southern Canada Basin (Taylor et al., 1981; Laxon and McAdoo, 1994). To better understand the opening history of the southern Canada Basin, the Naval Research Laboratory, in conjunction with the University of Texas Institute for Geophysics, undertook an aerogeophysical (gravity, magnetics and sea-surface topography) study in 1996 and 1997 in this region as part of a multi-year effort to determine the structure and evolution of the ice-covered Arctic Basins. Primary tracks were spaced at 10-15 km with cross-tracks at 75-90 km spacing. The older aeromagnetics obliquely cross the new data allowing a joint leveling of the data sets and result in a significant densification of the available aeromagnetic coverage of the region. The new data permit a better identification of patterns in the magnetic anomalies and structural lineations in the gravity data, allowing us to interpret the tectonic evolution of this region with greater certainty than was previously possible. The central gravity low is located asymmetrically eastward of the center of a broad wedge-shaped gravity high in the center of the basin. Three hundred km from Mackenzie Delta, the gravity low changes strike by 20 degrees and is segmented on a length scale of approximately 50 km northward of the bend. A bilaterally symmetric pattern of magnetic lineations some 300 km wide is centered over the gravity low strengthening the claim that this low represents an extinct spreading axis. However, the straightforward pattern in the middle of the basin does not continue towards the margins. The fossil axis appears to have propagated southward into the basin replacing an earlier spreading configuration to the west. Opening was originally about a pole in the Mackenzie Delta. Spreading later commenced about a pole 500 km to the southwest. The rotational pole later shifted eastward again, directly south of the original pole, for the final phase of opening. The asymmetry in location of the fossil axis with respect to the margins and the high gravity wedge are explained by these changes in spreading pattern. Traces of the earlier spreading episode are visible in the magnetics to the west. The pattern appears to change yet again in the region between the Alaska margin and the southern Chukchi Borderlands. In spite of the complexities the overall pattern remains consistent with the formation of the southern Canada Basin by rotation of the North Slope away from the Canadian margin around a set of poles somewhere near the Mackenzie Delta. Overlap in the reconstruction of the Chukchi Borderlands is eliminated by removal of the apparent extension and rotation within the Borderland and North Chukchi Basin. |
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Last Modified: October 8, 1999
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