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Abstract:

A number of configurations for supercontinent Columbia have been suggested since it was originally proposed nearly three decades ago. The arrangement of continents is based on evidence including sedimentary provenance, metallogenesis, shared igneous belts and deformational histories, and paleomagnetic compatibility. However, these methods do not provide more than approximate positioning of the continents. Data acquired from the Ogilvie Mountains, northern Yukon, Canada has allowed us to accurately position the northeastern margin of Australia with the northwestern margin of Laurentia. Sandstone from unit PR1 of the lower Fifteenmile group, in the Coal Creek inlier, yielded a near-unimodal population of well-faceted detrital zircon that suggests limited transport of sediment from a proximal source. Notably, the data lie on a discordia line with an upper intercept age of 1499+ or -3 Ma, which falls into the North American Magmatic Gap (NAMG; 1610-1490 Ma), a period of magmatic quiescence in Laurentia. Without sources for this population in Laurentia, we appeal to sources on other continents. However, even globally there are few sources for this population. The Williams and Naraku batholiths in the Mt. Isa inlier of northeastern Australia, with crystallization ages ranging from 1493+ or -8 Ma to 1508+ or -4 Ma, are possible sources whose mineralogy compares favourably to that of the sandstones from which our detrital zircon grains were derived. In addition, paleomagnetic reconstructions show Australia adjacent to Laurentia's western margin in the early Mesoproterozoic. The plutons were exhumed between 1460 and 1420 Ma, and likely formed an active, eroding highland in the Australian part of Columbia. We suggest sediment derived from these plutons was carried eastward by a short, direct river system and deposited into the PR1 marine basin. Formation of the PR1 basin coincides with the formation of the southern Cordilleran Belt-Purcell, Hess Canyon, and Trampas basins. These basins also have detrital zircon populations that fall into the NAMG, suggesting that sediment was derived from a non-Laurentian westerly source, likely Australia and Antarctica. Collectively, these basins record the onset of Columbia breakup along the length of the western margin of Laurentia, from Yukon to Arizona.

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