Sedimentology, Geochemistry, and Geochronology of unit PR1 of the lower Fifteenmile group and the Pinguicula Group, Wernecke and Ogilvie Mountains, Yukon, Canada: Mesoproterozoic environments and paleocontinental reconstructions

摘要

Unit PR1 of the lower Fifteenmile group and the Pinguicula Group are exposed in Ogilvie and Wernecke mountains, Yukon, Canada. Unit PR1 records deposition of turbiditic interbedded sandstone and mudstone with scattered carbonate olistoliths. The Pinguicula Group records deposition of non-cyclic siliciclastic and carbonate strata on low-energy slopes affected by rare high-energy deposits. The Pinguicula Group comprises three newly formalised formations: the Mount Landreville, Pass Mountain, and Rubble Creek (formerly units A, B, and C, respectively). The older unit PR1 has a near-unimodal detrital zircon population with an age of 1499 ± 2.7 Ma and εNd(t) values from -8.17 to 3.92. Overall, detrital zircon data from the Pinguicula Group display a polymodal detrital zircon population with a maximum age of 1322 ± 23 Ma and εNd(t) values from -1.55 to 1.12. C-isotopic analyses from the Pinguicula Group record average δ13C values ranging from -0.64 to +1.6‰ Vienna Pee Dee Belemnite (VPDB). Stratigraphic correlations between the Pinguicula Group in the Wernecke and Hart River inliers have been confirmed using lithostratigraphy, combined with detrital zircon U-Pb geochronology, Sm-Nd, and C-isotope signatures. The Pinguicula Group and unit PR1 are no longer considered correlative based on differences in detrital zircon signatures and Sm-Nd isotopic data. Detrital zircon ages from unit PR1 fall into the North American Magmatic Gap (NAMG; 1610-1490 Ma) and therefore sediment in unit PR1 is interpreted to have been from the Mt. Isa inlier in northeastern Australia. The PR1 basin may have been deposited as early as 1460 Ma on Laurentia’s northwestern margin, coincident with the Belt-Purcell, Yankee Joe/Defiance, and Trampas basins that formed during the break-up of supercontinent Columbia. These basins derived some or all of their sediment from Australia and the Mawson continent. Younger Mesoproterozoic strata, deposited after 1.45 Ga, including the Missoula Group and Marqueñas Formation, lack NAMG-aged zircons and instead record a shift in sediment provenance to southern Laurentia as north Australia and the Mawson continent rifted from Laurentia’s western margin. The Pinguicula Group (1322 Ma) was probably fed from southern Laurentian Granite-Rhyolite provinces with NAMG-aged zircons recycled from older Mesoproterozoic strata.