Abstract

The Canadian Arctic Rift System is a dormant Atlantic spreading centre that was propagated northwestward from the Mid-Atlantic Ridge into the North American Plate. The plate was stretched and fragmented into large and small sub-plates.

Conventional plate tectonic theories suggest that the rift system caused Greenland to move as a rigid body more than 220 km to the northeast along a strike slip fault. Baffin Bay and Labrador Sea formed in the gap behind.

In contrast to such theories, the author’s thesis is that the rift system caused Greenland and Canada to move apart a much shorter distance, by rotation. The broadly triangular seaway between them, as wide as 1000 km, resulted from a combination of processes: (1) stretching of the continental lithosphere; (2) physical drift of lithospheric blocks by rotation; and (3) the isolation and submergence of an intervening continental remnant. The three processes reached an advanced stage in the southeast, where the rift system is mature and connects with the North Atlantic Ocean. All three diminished northwestward, and largely died out near the terminus of the rift system in Arctic Canada.

The oceanic spreading centre dissipates into the stretched and broken North American Plate. The North American Plate here contains several large sub-plates, each of which in turn was broken into successively smaller sub-plates and fault blocks. Some of these units are now above sea level as islands and island groups; others are below sea level as aulacogens and rift valleys.

Major plate rotation occurred about a broad transform pivot in the Canadian Arctic. Southeast of the pivot lithospheric stretching occurred by listric faulting in upper levels of the lithosphere, and by distributed flow at depth. The listric faults produced fragmentation which diminished northwestward toward the pivot and allowed the plates to diverge. Beyond the pivot where the major blocks were converging, there was compressional deformation which increased northward away from the pivot.

Near the terminus of the spreading centre, wide marginal parts of the separating plates behaved non-rigidly by stretching. This allowed the plates to bend slightly as they rotated apart, and amplified the separation of the more distant non-deforming parts of the diverging plates.

Plate rotation was not centred on a single fixed point. Instead rotation took place about a broad transform pivot area that migrated northwest through time. In addition, there were lesser transform pivots located between the numerous smaller sub-plates that also were rotating away from each other.