PROTEROZOIC WILSON CYCLICITY AND ITS APPLICATION TO LAURENTIA-AUSTRALIA INTERACTIONS

Proterozoic inliers in Yukon, Canada, have provided new constraints on the geological history and paleogeography of northwestern Laurentia. The region is characterized by Proterozoic successions of clastic and carbonate rock with a cumulate thickness of over 25 km. However, the sedimentation was punctuated by events of deformation, metamorphism, magmatism and hydrothermal brecciation. Detailed examination of these events has led to a new view of crustal evolution that supplants older models which focused on repeated extension and basin formation. The new information shows that northwestern Laurentia was an active participant in intercontinental activity from the late Paleoproterozoic to the Neoproterozoic. At 1.8 Ga, Laurentia was embedded within the supercontinent Nuna/Columbia. At ca. 1.7 Ga, the northwestern part of Nuna underwent rifting but at ca. 1.66 Ga experienced Laramide-style contraction. Renewed extension led to separation of a continental fragment which became a portion of Australia. An intervening ocean basin formed and a passive margin developed on Laurentia. Collapse of the ocean basin led to inversion and metamorphism of the passive margin strata, followed by terrane obduction and collision with Australia (including East Antarctica). At 1.60 Ga, the Gawler craton of Australia was adjacent to northwestern Laurentia and a sedimentary overlap assemblage was deposited across the suture. Between 1.60 Ga and 1.59 Ga, surges of fluids led to formation of a shared iron-oxide copper gold province. By 1.45 Ga, Australia had translated southward along the suture, and the Mt. Isa region became juxtaposed with northwest Laurentia. Sediment from Australia poured onto Laurentia and helped to fill a series of transtensional basins, including the Belt basin, from Yukon to the southwestern USA. By 1.3 Ga, Australia had again separated from Laurentia but was reconnected during the Grenville orogeny from 1.2-1.0 Ga as part of the assembly of supercontinent Rodinia. Finally, Australia moved away from Laurentia during continent-long rifting/drifting in the late Neoproterozoic to early Phanerozoic, leading to formation of the Paleozoic miogeocline on Laurentia. The separations and reconnections involving Australia constitute Wilson cyclicity with collisions at 1.8, 1.6 and 1.1 Ga.