AUSTRALIA-LAURENTIA RELATIONS IN THE LATE PALEOPROTEROZOIC TO MESOPROTEROZOIC: A WILSON CYCLE FOLLOWED BY SINISTRAL TRANSLATION

The late Paleoproterozoic and Mesoproterozoic evolution of northwestern Laurentia involved pulses of extensional sedimentation interspersed with magmatism, deformation, metamorphism and hydrothermal brecciation. It is now evident that northwestern Laurentia, as part of an evolving supercontinent named Nuna and Columbia, was involved in a Wilson cycle and sinistral displacement relative to Australia-Antarctica during the late Paleoproterozoic. Laurentia, the cratonic core of supercontinent Nuna, formed during widespread orogenesis from 1.9-1.8 Ga. As early as 1.75 Ga, Nuna began rifting and by 1.7 Ga northwestern Laurentia had separated from continental fragments including portions of Australia and possibly East Antarctica and South China. The resulting ocean basin was consumed by 1.60 Ga which led to collision of Laurentia with Australia and East Antarctica. The re-attachment of Australia to Laurentia completed a Wilson cycle and heralded the formation of supercontinent Columbia. During the collision, an intervening arc terrane named Bonnetia was obducted onto Laurentia. The obduction was followed by sedimentation and surges of hydrothermal fluids to form Wernecke Breccia within Laurentia at 1.60 Ga. The hydrothermal activity also affected the adjacent Gawler Craton and generated the Olympic Dam breccia complex at ca. 1.59 Ga. Subsequent sedimentary successions on Laurentia include unit PR1 of the Fifteenmile Group in Yukon, the Belt-Purcell Supergroup in southwestern Canada and the northwestern United States, and related successions as far south as Arizona. Detrital zircon populations from these extensional basins reflect sediment input from Australia and East Antarctica between 1.5 and 1.45 Ga. After ca. 1.45 Ga, Australia either ceased to be a highland relative to Columbia, or was separated from Columbia by a narrow seaway. From 1.6 to 1.4 Ga, the Australia-Antarctica landmass migrated from northwestern to southwestern Laurentia along a sinistral translational system, coming to rest adjacent to the present-day southwestern United States where midcontinent granites stitched the continents together. Late in the Mesoproterozoic, a new supercontinent named Rodinia began to form although a full understanding of the Columbia-Rodinia transition remains elusive.