Detrital Zircon Geochronology of the Queen Charlotte Group, Haida Gwaii, British Columbia
Date
2019-01-17
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Abstract
Marine clastic strata of the Queen Charlotte Group (QCG), exposed within Skidegate Inlet on Haida Gwaii, British Columbia, Canada, provide a comprehensive stratigraphic record of Cretaceous forearc deposition on the Wrangellia Terrane. These exposures include the Aptian to Campanian Longarm, Haida, Skidegate, Honna, and Tarundl formations. Detrital zircons from these strata provide a unique opportunity to test linkages between the Wrangellia-Alexander, Taku and Yukon-Tanana terranes in the Cretaceous. Twelve samples were collected through the Cretaceous stratigraphic succession and 300 U-Pb measurements were obtained for each sample by LA-ICP-MS. Detrital zircon populations are dominated by two Mesozoic sub-populations with modes at ~150 Ma and ~90 Ma. These ages indicate QCG strata derive predominantly from rocks of the northwest Coast Plutonic Complex (CPC) to the east where rocks of this age are common. A small but consistent Paleozoic (~400 to 430 Ma) population in samples from the Longarm, Haida, Skidegate and Honna formations suggests a linkage to the Alexander Terrane during the Early to Late-Cretaceous. The youngest strata sampled, the Latest Campanian Tarundl Formation, yielded detrital zircons with complex U-Pb systematics indicative of inheritance. Cores from the Tarundl Formation yield dates of 300-400 Ma and 1000-2800 Ma, similar to sedimentary rocks of the Yukon-Tanana Terrane. Zircon rims within the youngest sub-population yield a single age (86.7 ± 1.2 Ma; MSWD 8.0) suggesting the Tarundl Formation derives from a restricted source area and potentially a single magmatic body. The ages of inherited cores indicate this source likely intruded rocks of the Yukon-Tanana Terrane such as the basal Port Houghton assemblage.
Maximum depositional ages (MDAs) indicate syn-magmatic sedimentation from the Aptian to Campanian, which is consistent with biostratigraphic age constraints (e.g. McLearn, 1972; Haggart, 1991; Haggart, 2009). However, clustering of the MDA suggests punctuated sedimentation that was likely deposited by migrating channel systems. Detrital zircon ages from rocks of the QCG indicate derivation was from source areas located west of the Coast Shear Zone (CSZ). Therefore, a linkage to sources east of the CSZ is not necessary to explain provenance for the Queen Charlotte Group.
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Keywords
Late Cretaceous, Tectonics
Citation
Dorsey, C. (2019). Detrital Zircon Geochronology of the Queen Charlotte Group, Haida Gwaii, British Columbia (Master's thesis, University of Calgary, Calgary, Canada). Retrieved from https://prism.ucalgary.ca.