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Geology of the central Moresby Island region, Queen Charlotte Islands, (Haida Gwaii) British Columbia Taite, Susan Patricia


The Queen Charlotte Islands represent the most outboard exposure of Wrangellia in the Canadian Cordillera. This study analyzes the structural and stratigraphic history of the central Moresby Island area, and correlates this history with ongoing and previous studies in the Queen Charlotte Islands. The stratigraphic succession preserved in central Moresby Island comprises marine volcanic and sedimentary rocks of the Triassic Karmutsen Formation and Kunga Group, Middle Jurassic arc volcanic rocks of the Yakoun Group, marine sedimentary rocks of the Longarm Formation and Queen Charlotte Group, and Tertiary volcanic rocks. The Karmutsen Formation and Kunga Group rocks exposed in central Moresby Island formed during a widespread Triassic volcanic event followed by marine carbonate and clastic sedimentation. Coarse clastic lithologies in the Kunga Group indicate a volcanic provenance as early as the Norian. The Early to Middle Jurassic marine sedimentary rocks of the Maude Group, present elsewhere in the Queen Charlotte Islands, are absent in central Moresby Island. Oldest rocks of the clastic Longarm Formation in central Moresby Island are of Hauterivian age, and the conformably overlying Queen Charlotte Group extends into at least the Turonian. Both field and petrographic evidence suggest two distinct suites of Tertiary volcanic rocks exist in central Moresby Island. Dominant megascopic structures in central Moresby Island are dominated by north, northeast and northwest-trending fault sets. Folding is common in stratified Kunga Group lithologies, and only of minor importance in younger successions. The deformational history outlines five events: Middle Jurassic shortening, Middle to Late Jurassic extension, post-Cretaceous and pre-Tertiary shortening, post-Cretaceous and pre-(syn ?) Tertiary extension, and a syn (?) to post-Tertiary extension. The structural history outlined for the central Moresby Island area provides several refinements to pre-existing models. It provides evidence that Middle Jurassic shortening continued into and possibly outlasted Yakoun Group arc volcanism. Cretaceous block faulting, documented on Graham Island and northern Moresby Island, extended into central Moresby Island. Asymmetric south-directed Tertiary extension, documented on southern Moresby Island, also extended into central Moresby Island, and has implications to the offset history of regional faults.

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