Kinematics and deformation history of the Cross Lake greenstone belt (Alberta)

Greenstone belts are a common feature of Archean terrains. However, the tectonic environment for Archean earth remains in hot debate: did vertical or horizontal crustal movement dominate the Archean Eon? Small-scale structural analysis is applied to a late Archean greenstone belt in the Superior Province of the Canadian Shield in order to test the two end member hypotheses. Detailed structural analysis reveals that the Cross Lake greenstone belt has undergone three major events of deformation. The early event of ESE-WNW convergence and crustal thickening initiated folding and produced northeast-trending shear zones. The configuration of the northwestern Cross Lake area is largely due to this event. This was followed by the juxtaposition of the Nelson River-Pipestone Lake high-strain zone. The last event was the juxtaposition of the Eves Rapids Complex with the development of a major northeast-trending fault, which overprints all previous deformation. The strain geometry and structural features suggest that the first event of crustal thickening likely involved vertical tectonics induced by gravitational instability rather than transpression.