Geoscience Map 2011-05 Geology, Geochronology, Lithogeochemistry and Metamorphism of the Nimpkish-Telegraph Cove Area, Northern Vancouver Island (NTS 092L/07 and part of 092L/10) 1:50 000 scale
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Geoscience Map 2011-5 (1:50 000-scale) is the final map in a series of five new geological maps (Geoscience Maps 2011-1 to 2011-5) of northern Vancouver Island which together provide a revised Early Mesozoic stratigraphic framework and Mesozoic-Tertiary plutonic history for southern Wrangellia. Geoscience Map 2011-5 describes the geology, geochronology, lithogeochemistry and metamorphism of the Nimpkish – Telegraph Cove area (NTS 092L/07 and part of 92L/10). The map area is underlain by a folded and faulted sequence of Late Triassic volcanic and sedimentary rocks of the Vancouver and Bonanza groups intruded by granitoids of the Early to Middle Jurassic Island Plutonic Suite. The deformed Triassic rocks are unconformably overlain by Upper Cretaceous marine clastics (Nanaimo Group equivalents) and intruded by rare Tertiary dykes. The Late Triassic Quatsino limestone thins radically from west to east across the map area, reaching a maximum thickness of ~800 m between Nimpkish and Bonanza lakes and a minimum thickness of <250 m in coastal exposures west of Beaver Cove. Small base-metal skarn occurrences are concentrated between Bonanza and Nimpkish lakes where the limestone is thickest near contacts with Early-Middle Jurassic granitoid intrusions of the Island Plutonic Suite (e.g. northern margins of the Noomas Creek Pluton and Nimpkish Batholith west of Bonanza Lake). The underlying Karmutsen Formation has a minimum estimated thickness of ~6 km and comprises a basal submarine pillowed basalt unit (>3 km), a middle hyaloclastite unit (~1.5 km) and an upper subaerial flow unit (>1.5 km). This stratigraphy is well-exposed in oblique section along the east coast of the island between Telegraph Cove and Robson Bight. Younger augite-plagioclase-phyric volcanic sequences in the area are assigned to the Late Triassic Parson Bay Formation; Early to Middle Jurassic volcanic stratigraphy equivalent to the Le Mare Lake and Holberg volcanic units to the west and north, respectively, are entirely lacking. Major structures in the area include steeply dipping, northerly and northwesterly-trending faults (e.g. Huston Lake, Nimpkish and Bonanza Lake faults), and an intersecting set of northeasterly-oriented structures in the northernmost part of the map area. A major north-northwesterly-trending synclinal axis delineated by strata of the Parson Bay and Quatsino formations passes through the crest of the Hankin Range and extends northwards to the Beaver Cove Fault. Regional metamorphism is generally characterized by very low-grade mineral assemblages (prehnite-pumpellyite to zeolite facies) except in the vicinity of faults and intrusive contacts where the rocks may reach upper greenschist to amphibolite grade, respectively.
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