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TitleThe plutonic rocks of Vancouver Island, British Colombia: their petrography, chemistry, age and emplacement
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AuthorCarson, D J T
SourceGeological Survey of Canada, Paper 72-44, 1973, 81 pages (3 sheets), https://doi.org/10.4095/102271
Year1973
PublisherDepartment of Energy, Mines and Resources Canada
Documentserial
Lang.English
MapsPublication contains 1 map
Map Info.geological, bedrock geology, 1:1,203,840
Mediapaper; on-line; digital
File formatpdf
ProvinceBritish Columbia; Western offshore region
NTS92B/05; 92B/06; 92B/11; 92B/12; 92B/13; 92B/14; 92C/07; 92C/08; 92C/09; 92C/10; 92C/11; 92C/13; 92C/14; 92C/15; 92C/16; 92E/01; 92E/07; 92E/08; 92E/09; 92E/10; 92E/11; 92E/13; 92E/14; 92E/15; 92E/16; 92F/01; 92F/02; 92F/03; 92F/04; 92F/05; 92F/06; 92F/07; 92F/08; 92F/09; 92F/10; 92F/11; 92F/12; 92F/13; 92F/14; 92F/15; 92G/03; 92G/04; 92G/05; 92K/03; 92K/04; 92K/05; 92L/01; 92L/02; 92L/03; 92L/04; 92L/05; 92L/06; 92L/07; 92L/08; 92L/09; 92L/10; 92L/11; 92L/12; 92L/13; 92L/14; 92L/15; 102I/01; 102I/08; 102I/09; 102I/16
AreaVancouver Island; Victoria
Lat/Long WENS-128.5000 -123.0000 51.0000 48.2500
Subjectsregional geology; tectonics; stratigraphy; geophysics; geochronology; geochemistry; igneous and metamorphic petrology; copper; gold; modal analyses; potassium argon dates; variation trends; bedrock geology; lithology; igneous rocks; plutonic rocks; Alberni Plutons; Bedwell River Batholith; Bonanza Formation; Cache Creek Group; Cape Scott-rupert Arm Pltn; Coast Range Orogeny; Karmutsen Formation; Karmutsen Volcanics; Nanaimo Group; Nanaimo River Batholith; Nimpkish-bonanza Pluton; Nookta Batholith; Quatsino Formation; Quinsam Batholith; Saanich Granodiorites; Sicker Group; Sooke Intrusives; Tofino Inlet Pluton; Ucona Batholith; Vancouver Group; Phanerozoic; Cenozoic; Tertiary; Mesozoic; Cretaceous; Jurassic
Illustrationsgeochronological charts; geological sketch maps; tables; ternary diagrams; geochemical plots; schematic representations; photomicrographs; photographs
Released1973 03 01; 2014 04 11
AbstractMost plutons of Vancouver Island were emplaced between mid-Early and mid -Late Jurassic (approximately 150 to 180 million years ago), The majority of these we re intruded soon after an Early(?) to Middle Jurassic interval of broad regional folding. The Jurassic plutons are granodiorite and quartz diorite, with minor diorite, gabbro, and quartz monzonite, and rare granite. Most are upper mesozonal and are medium grained with granitic texture, but some epizonal porphyries and catazonal(?) gneisses are also present. Early to Middle Tertiary epizonal plutons (approximately 35 to 60 million year s) are much less abundant than Jurassic plutons. They were emplaced during part of an extended interval of block faulting and are quartz diorite, dacite porphyry, and gabbro, with minor granodiorite and quartz monzonite. Limited evidence suggests that some dioritic gneisses and quartz monzonite on the west coast may have crystallized during the Late Cretaceous. The plutonic rocks of Vancouver Island may be divided into three northwest-trending zones of differing compositions and textures. Quartz diorites and granodiorites low in K-feldspar predominate in the structurally elevated axial area. They are flanked along the east and northeast by a zone containing granodioritic plutons, most of which are relatively homogeneous, and along the west and southwest by another zone containing a wider variety of plutonic rocks that range in composition from granite (very minor) to peridotite (rare ), but have an average granodioritic composition similar to that of the eastern zone. Plutonic gneisses, and complex plutons with extensive border migmatite zones, are common only in the western belt, This over all northwest-trending textural - compositional zoning is somewhat similar to zoning of the plutonic rocks of the Coast Intrusions of mainland British Columbia. Jurassic plutons occur throughout Vancouver Island but the known Tertiary plutons are restricted to the western belt and to two zones that cross the northwesterly structural trend of the island. The chemistry of the plutons of known Jurassic age differs some what from that of the Tertiary plutons although there is some overlap and they appear to have been derived from similar parental material. Jurassic differentiation trends show similarities to those of the southern California batholith. The known Jurassic plutons contain more Ca and Fe, and possibly K, and less Na than the Tertiary plutons. These differences may have been the results o f greater assimilation of host rocks combined with more advanced stages of differentiation by the deeper- seated Jurassic plutons. During emplacement, many Jurassic plutons advanced passively upward in competent volcanic rocks but spread laterally and forcibly in less competent sedimentary rocks. The net effects were the strong deformation of host rocks, the accumulation of magma, and the deposition of abundant Cu-Fe skarn deposits (Zeballos Iron, Coast Copper, etc.) at the stratigraphic interval that included the uppermost Karmutsen Formation, the Quatsino limestone and the lower Bonanza Formation. Many of the intrusive bodies, including some of batholithic proportions, assumed roughly horizontal and sheetlike forms. High-level offshoots of these bodies intruded upward into the Bonanza Formation and many reached the surface, supplying volcanic material to the upper Bonanza Formation. Some of these offshoots have associated porphyry copper deposits (Island Copper, etc.). Most Tertiary stocks and dyke-like bodies were forcibly emplaced in subvolcanic environments. Intrusive and explosive breccias are common, Some of the Tertiary plutons are associated with porphyry copper deposits (Catface, etc.) and copper or gold veins (Mount Washington, Privateer, etc.). The Mount Washington intrusive complex consists of a centrally located quartz diorite stock with a peripheral diatreme and other irregularly shaped explosion breccias, and radiating sills and laccolithic tongues of dacite porphyry intruding gently-dipping Late Cretaceous sediments of the Nanaimo Group that surround the stock. Extensive dacite porphyry laccoliths and sills were emplaced at several other localities by lateral extension of stocks and dykes that penetrated upward into the lower Nanaimo Group. Large sill-like(?) gabbro plutons cut the Eocene Metchosin volcanics in southern Vancouver Island, where as smaller trondhjemite plutons of the same area are stocks.
GEOSCAN ID102271