GSA Annual Meeting in Phoenix, Arizona, USA - 2019

Paper No. 11-5
Presentation Time: 9:15 AM


THORKELSON, Derek J., Earth Sciences, Simon Fraser University, Burnaby, BC V5A 1S6, Canada and JOHNSON, Bradford J., Arizona Geological Survey, University of Arizona, 1955 E 6th St, Tucson, AZ 85721

The late Paleoproterozoic to Mesoproterozoic history of northwestern Canada compares favourably with that of the southwestern United States. Both regions are characterized by complex orogens along the paleo-margin of Laurentia. In northwestern Canada, a passive continental margin and a series of interior basins formed between 1.8 and 1.6 Ga. Two main pulses of deformation, named the Forward and Racklan orogenies, led to a broad orogen involving basin inversion and thin- and thick-skinned shortening. These events ended with the obduction of an oceanic terrane and collision with Australia, and consolidation of the supercontinent Nuna. Erosion and subsidence led to deposition at 1.5 Ga and magmatism at 1.38 Ga, with the latter signifying continental separation of Australia from Laurentia. Subsequent erosion and subsidence led to renewed deposition at 1.3 Ga. Metamorphism and magmatism at 1.1 Ga likely signifies renewed convergence with Australia. A series of Neoproterozoic events heralded the development of the Paleozoic continental margin. The Racklan and Forward events are broadly similar to the Yavapai and Mazatzal (sensu lato) orogenies. In both regions, the Laurentian margin was subjected to contraction, obduction and collision in the Late Paleoproterozoic. The 1.5-1.3 Ga unconformity in northwestern Canada may correlate with the Mesoproterozoic East Kootenay orogeny of southwestern Canada and the Picuris orogeny in the southwestern U.S. The 1.1 Ga deformation in northwestern Canada correlates with Grenville-age deformation in the western and southwestern United States and signifies the formation of Rodinia.

Taken together, these comparisons reveal that the western and southern margins of Laurentia share a broadly similar tectonic history from 1.8 Ga onward. As such, attempts to reconstruct continental configurations need to consider a range of positions for Australia and Antarctica along the evolving western Laurentian margin. Our current model places the Gawler region of Australia alongside northwestern Canada in the late Paleoproterozoic. A combination of extensional, contractional and possibly strike-slip events led to a more southern position for Australia and Antarctica in the Mesoproterozoic and Neoproterozoic.