Detrital zircons from the Nanaimo basin, Vancouver Island, British Columbia: An independent test of Late Cretaceous to Cenozoic northward translation. Issue 5 (8th May 2017)

• Record Type: Journal Article
• Authors: Matthews, W. A.; Guest, B.; Coutts, D.; Bain, H.; Hubbard, S.
• Is Part Of: Tectonics. Volume 36:Issue 5(2017)
• Page Start: 854
• Page End: 876
• Publication Date: 2017-05-08
• Subjects: geochronology -- plate tectonics -- paleomagnetism; Geology, Structural -- Periodicals; 551.8
• DOI: 10.1002/2017TC004531
• Languages: English
• ISSNs: 0278-7407

Abstract

Abstract: The development of the Cordilleran orogen of western North American is disputed despite a century of study. Paleomagnetic observations require large‐scale dextral displacements of crustal fragments along the western margin of North America, from low latitudes to moderate latitudes during the Cretaceous‐Paleogene. A lack of corroborating geological evidence for large‐scale (>1500 km) displacements has prevented the widespread integration of paleomagnetic data into most contemporary tectonic models for the margin. Here we use detrital zircons from the Nanaimo basin, southwestern British Columbia, Canada as an independent test of its Late Cretaceous paleogeographic position. We compare 4310 detrital zircon U/Pb dates from 16 samples to potential source areas in western North America to test hypothesized northern and southern Late Cretaceous paleogeographic positions. Our detrital zircon data suggest that sediment in the Nanaimo basin derives from either a geographically restricted portion of the Belt‐Purcell basin or the Mojave‐Sonoran region of southwestern North America. A paleogeographic position for the basin adjacent to the Mojave‐Sonoran region is preferred as it is consistent with the paleomagnetic results, but further geological, isotopic, or geophysical data are required to rule out a Belt‐Purcell source. Plain Language Summary: The North American Cordillera is one of the most studied continent scale orogenic belts on Earth, and as such is commonly used as a model for understanding tectonic processes in less well known regions. The theories developed in the Cordillera are underpinned by an assumption that the general evolution of the North American plate margin over the last ~200 Ma is well understood with accretion of terrains being the dominant process. This assumption has persisted for the last 40 years despite a growing paleomagnetic and paleobotanical data sets that suggests that the paradigm is actually false and N‐S terrain migration may dominate processes in some parts of the cordillera. With this article, we use a detrital zircon data set to independently test the Cretaceous paleogeographic position of the Nanaimo basin of Vancouver Island, British Columbia, Canada. Our provenance analysis shows that Nanaimo Group sediments may derive from a geographically restricted region of the Belt‐Purcell basin in Idaho or from the Mojave‐Sonoran region of the southwest United States and northern Mexico. Our results are most consistent with derivation from the Mojave‐Sonoran region and support the paleomagnetic estimates for the western Cordilleran terranes. Key Points: Paleomagnetic data sets require ~2000 km of northward translation of parts of the western Cordillera since the Late Cretaceous Detrital zircons in the Nanaimo Basin derive from either the Lemhi subbasin of Idaho or the Mojave‐Sonoran region of the southwest U.S. A southerly Late Cretaceous paleogeographic position, consistent with the paleomagnetic data sets, is preferred