U-PB DETRITAL ZIRCON ANALYSIS OF THE QUEEN CHARLOTTE GROUP, HAIDA GWAII, BRITISH COLUMBIA

Marine clastic strata of the Queen Charlotte Group (QCG), exposed within Skidegate Inlet on Haida Gwaii, British Columbia, Canada, provide a near-complete stratigraphic record of Cretaceous forearc deposition on the Wrangellia terrane. These exposures include the Valanginian 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.

Twelve samples were collected through the entire 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 subpopulations with modes at ~150 Ma and ~95 Ma. These ages indicate QCG strata derive predominantly from rocks of the Coast Plutonic Complex 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 yield a single age (87 ± 3 Ma) suggesting the Tarundl Formation could derive from a restricted source area. The ages of inherited cores indicate this source likely intruded rocks of the Yukon-Tanana terrane such as the Endicott or Tracy Arm assemblage.

Detrital zircon results from the QCG indicate a change in sediment provenance in the Late Cretaceous. Valanginian to Santonian rocks of the Longarm, Haida, Skidegate, and Honna Formation derive from the Coast Plutonic Complex with some input from the Alexander Terrane whereas the late Campanian Tarundl Formation contains zircon populations that derive from the Yukon-Tanana terrane. This change in provenance coincides with Campanian shortening that led to deepening of the basin and uplift and exposure of basal Yukon-Tanana assemblages to the east.