Geochemical and Nd-Sr-Pb isotopic evidence on the origin and geodynamic evolution of mid-Cretaceous continental arc volcanic rocks of the Spences Bridge Group, south-central British Columbia

2002 ◽  
Vol 37 (2) ◽  
pp. 167-186 ◽  
Author(s):  
Alan D. Smith ◽  
Derek Thorkelson
Keyword(s):  
British Columbia ◽  
Volcanic Rocks ◽  
Geodynamic Evolution ◽  
Isotopic Evidence ◽  
South Central ◽  
Continental Arc ◽  
Bridge Group

The conglomerate of Churn Creek: Late Cretaceous basin evolution along the Insular–Intermontane superterrane boundary, southern British Columbia

2001 ◽  
Vol 38 (1) ◽  
pp. 59-73
Author(s):  
J W Riesterer ◽  
J Brian Mahoney ◽  
Paul Karl Link
Keyword(s):  
British Columbia ◽  
Late Cretaceous ◽  
Upper Cretaceous ◽  
Volcanic Rocks ◽  
Clastic Rocks ◽  
South Central ◽  
Lower Member ◽  
Volcanic Source ◽  
Braided Stream ◽  
Bridge Group

Upper Cretaceous coarse clastic rocks exposed in the canyon of Churn Creek, south-central British Columbia, record active basin tectonism and coeval volcanism adjacent to the boundary between the Intermontane and Insular superterranes. Mid to late Albian (~104 Ma U–Pb), calc-alkaline andesite and basaltic andesite flows, with minor conglomerate and reworked epiclastic deposits and tuffs correlative with the Spences Bridge Group of the Intermontane superterrane are exposed in the canyon. In depositional contact above the volcanic rocks is the conglomerate of Churn Creek, which contains a thick (>1 km) sequence of complexly intertonguing conglomerate and sandstone that is divided into two members composed of four lithofacies. The lower member was deposited unconformably on the underlying Albian volcanic unit and contains late Albian–Cenomanian chert-pebble (>50% chert) conglomerate and interbedded chert- and volcanic-lithic sandstone. It is interpreted to have been deposited in a braided stream system flowing from southeast to northwest. The source for the chert was most likely the Bridge River terrane, a Mississippian to Jurassic ocean floor assemblage located to the southwest of Churn Creek, south of the Yalakom fault. Gradationally overlying the lower member throughout much of the basin is a mixed chert, plutonic, and volcaniclastic lithofacies of the upper member. Plutonic debris was provided to the mixed and plutonic lithofacies of the upper member by the Little Basin pluton, which was uplifted along the northeast-directed Little Basin thrust fault on the southwest margin of the basin. The upper member also contains a volcanic-rich lithofacies composed of chaotic volcanic conglomerate and local lithic tuff derived from a coeval proximal volcanic source. The conglomerate of Churn Creek records active northeast-vergent compressional tectonism and development of piggyback basins along the boundary between the Insular and Intermontane superterranes during Albian–Santonian time. The conglomerate of Churn Creek has been correlated to the Silverquick – Powell Creek succession of the Methow terrane, based on age, stratigraphic, lithologic, structural, geochemical, and paleomagnetic similarities, and may, therefore, represent an overlap assemblage linking the superterranes in the Late Cretaceous.

A Paleozoic Zircon Age of the Westcoast Crystalline Complex of Vancouver Island, British Columbia

1974 ◽  
Vol 11 (12) ◽  
pp. 1717-1722 ◽  
Author(s):  
J. E. Muller ◽  
R. K. Wanless ◽  
W. D. Loveridge
Keyword(s):  
British Columbia ◽  
Volcanic Rocks ◽  
Vancouver Island ◽  
Late Paleozoic ◽  
Basement Complex ◽  
Crystalline Complex ◽  
Zircon Age ◽  
Isotopic Evidence

Zircons from the Westcoast Crystalline Complex near Tofino, Vancouver Island, have yielded the following ages: 206Pb/238U = 265 ± 7 m.y.; 207Pb/235U = 263 ± 7 m.y.; and 206Pb/207Pb = 244 ± 20 m.y. A K–Ar date of an amphibolized dike from the same outcrop yielded 192 ± 9 m.y. This is the first supporting isotopic evidence that the 'basement' complex is derived from late Paleozoic Sicker volcanic rocks and was ultimately migmatized during the major Jurassic plutonic event of Vancouver Island.

Petrology and geochemistry of the Kamloops Group volcanics, British Columbia

1981 ◽  
Vol 18 (9) ◽  
pp. 1478-1491 ◽  
Author(s):  
Thomas E. Ewing
Keyword(s):  
British Columbia ◽  
Fractional Crystallization ◽  
Middle Eocene ◽  
Volcanic Rocks ◽  
Primary Source ◽  
Low Pressure ◽  
Rock Types ◽  
South Central ◽  
High K ◽  
Petrology And Geochemistry

The Kamloops Group is an alkali-rich calc-alkaline volcanic suite of Early to Middle Eocene age, widespread in south-central British Columbia. Rock types in the suite range from high-K basalt through andesite to rhyolite. The suite is characterized by relatively high K2O, Sr, and Ba, but low Zr, Ti, and Ni concentrations, only moderate Ce enrichment, and little or no Fe enrichment. Initial ratios 87Sr/86Sr are about 0.7040 in the western half, and about 0.7060 in the eastern half of the study area. No difference in chemistry or mineralogy marks this sharp transition. Chemically similar suites include the Absaroka–Gallatin suite in Wyoming and the lower San Juan (Summer Coon) suite in Colorado. The content of K2O at 60% SiO2 increases regularly eastward across southern British Columbia. The chemical data support the subduction-related continental arc origin of the Kamloops Group volcanics.The volcanic rocks consist in the main of augite–pigeonite andesites ranging from 52 to 62% silica, with subordinate quantities of olivine–augite–pigeonite basalt and biotite rhyodacite and rhyolite. The andesites and basalts were derived by a combination of low-pressure fractional crystallization, higher pressure fractional crystallization, and variable parental magmas, whereas low-pressure fractional crystallization of plagioclase, biotite, and apatite from parental basalt and andesite produced the rhyolites. The parental magmas were basalts and basaltic andesites with high K, Sr, and Ba. The primary source of these magmas is inferred to have been an alkali-enriched hydrous peridotite with neither plagioclase nor garnet present in the residuum.

Revised stratigraphic nomenclature and age determinations for mid-Cretaceous volcanic rocks in southwestern British Columbia

1989 ◽  
Vol 26 (10) ◽  
pp. 2016-2031 ◽  
Author(s):  
Derek J. Thorkelson ◽  
Glenn E. Rouse
Keyword(s):  
British Columbia ◽  
Volcanic Rocks ◽  
Fault System ◽  
Volcanic Stratigraphy ◽  
Clastic Rocks ◽  
Lower Unit ◽  
Basement Rocks ◽  
Lithostratigraphic Units ◽  
Bridge Group ◽  
Stratigraphic Nomenclature

Mid-Cretaceous volcanic and volcaniclastic rocks in southwestern British Columbia, east of the Fraser Fault System, constitute two principal lithostratigraphic units. The lower unit, a composite succession of basaltic to rhyolitic lavas and various clastic rocks, is exposed in a 215 km linear belt from near Pavilion to south of Princeton. The upper unit, mostly amygdaloidal andesite, is restricted to the centre of the belt between Spences Bridge and Kingsvale, where it overlies the lower unit and contiguous basement rocks. Both units were deposited subaerially, concurrent with folding and faulting, and share a contact that varies from gradational, near Kingsvale, to unconformable, near Spences Bridge.The names "Spences Bridge Group" and "Kingsvale Group" were used by several authors for various parts of the volcanic stratigraphy. We suggest revision of nomenclature whereby the lower and upper units are named "Pimainus Formation" and "Spius Formation", respectively; together they constitute the Spences Bridge Group. The term "Kingsvale Group" is abandoned.Assemblages of fossil leaves and palynomorphs, collected from one Spius and seven Pimainus localities, include several species of early angiosperms. A late Albian age is thereby indicated for both formations; this is largely corroborated by isotopic dates from the volcanic strata and cross-cutting granitic plutons.

Age and Correlation of the Kobau Group, Mount Kobau, British Columbia

1973 ◽  
Vol 10 (10) ◽  
pp. 1508-1518 ◽  
Author(s):  
Andrew V. Okulitch
Keyword(s):  
British Columbia ◽  
Volcanic Rocks ◽  
Metamorphic Rocks ◽  
Low Grade ◽  
South Central ◽  
Shuswap Metamorphic Complex ◽  
Basic Volcanic ◽  
Devonian Age ◽  
Tertiary Period ◽  
Okanagan Valley

The Kobau Group, found in south-central British Columbia, consists of highly deformed, low-grade metamorphic rocks derived from a succession of sedimentary and basic volcanic rocks of pre-Cretaceous, likely post-Devonian age. Deformation began in Carboniferous times and recurred with decreasing intensity up to the Tertiary Period. Possible correlative successions are found surrounding Mount Kobau. These include possibly late Paleozoic formations west and northwest of Mount Kobau, the Carboniferous to Permian Anarchist Group found south of the 49th parallel and east of the Okanagan Valley, the pre-Upper Triassic, possibly Mississippian Chapperon Group west of Vernon, and parts of the Shuswap Metamorphic Complex east of the Okanagan Valley. Prior to deposition of the Kobau Group, part of the Shuswap Complex was subjected to deformation, presumably in mid-Paleozoic time.

New U–Pb age constraints on latest Cretaceous magmatism and associated mineralization in the Fawnie Range, Nechako Plateau, central British Columbia

2001 ◽  
Vol 38 (4) ◽  
pp. 619-637 ◽  
Author(s):  
R M Friedman ◽  
L J Diakow ◽  
R A Lane ◽  
J K Mortensen
Keyword(s):  
British Columbia ◽  
Volcanic Rocks ◽  
Western Margin ◽  
Fine Grained ◽  
The North ◽  
Continental Arc ◽  
Igneous Activity ◽  
Minimum Age ◽  
Plateau Central ◽  
Cretaceous Magmatism

New U–Pb ages and K–Ar dates, primarily for rocks proximal to mineral occurrences in the Fawnie Range of central British Columbia, document latest Cretaceous (ca. 74–66 Ma) continental-arc igneous activity and date associated base and precious metal mineralization. U–Pb ages of ca. 73–69 Ma for the Capoose pluton and hypabyssal to extrusive garnet rhyolites at the Capoose prospect demonstrate a latest Cretaceous age for mineralization and a likely plutonic source for mineralizing fluids. A U–Pb age of ca. 67 Ma for a late mineralized felsic dyke and two K–Ar dates (ca. 70 and 68 Ma) for hornfelsed Jurassic volcanic rocks at the Blackwater–Davidson prospect constrain a latest Cretaceous age for mineralization. A U–Pb age of ca. 74 Ma for a fine grained diorite sill that cuts a significant epithermal gold vein at the Tsacha prospect places a minimum age on mineralization at this probable Jura-Cretaceous deposit and documents latest Cretaceous magmatism. Latest Cretaceous K–Ar dates are reported for an andesite flow adjacent to the Eocene Holy Cross deposit (ca. 66 Ma), about 35 km north of the Fawnie Range, and a Kasalka Group rhyolite (ca. 68 Ma) exposed near the western margin of the Nechako Plateau. Latest Cretaceous magmatism and mineralization in the Fawnie Range represent the waning stages of Bulkley suite magmatism and porphyry-style mineralization, which was concentrated along the western margin of the Nechako Plateau at circa 88–70 Ma. The distribution of latest Cretaceous arc igneous rocks along the North American Cordilleran is reviewed and tectonic implications discussed.

Eocene melting of Precambrian lithospheric mantle: Analcime-bearing volcanic rocks from the Challis–Kamloops belt of south central British Columbia

2003 ◽  
Vol 126 (3-4) ◽  
pp. 303-326 ◽  
Author(s):  
J. Dostal ◽  
K. Breitsprecher ◽  
B.N. Church ◽  
D. Thorkelson ◽  
T.S. Hamilton
Keyword(s):  
British Columbia ◽  
Lithospheric Mantle ◽  
Volcanic Rocks ◽  
South Central

Magmatic composition and tectonic setting of altered, volcanic rocks of the Fennell Formation, British Columbia

1984 ◽  
Vol 21 (7) ◽  
pp. 743-752 ◽  
Author(s):  
Pradeep K. Aggarwal ◽  
Toshitsugu Fujii ◽  
Bruce E. Nesbitt
Keyword(s):  
British Columbia ◽  
Marine Sediments ◽  
Tectonic Setting ◽  
Volcanic Rocks ◽  
Tholeiitic Basalt ◽  
Oceanic Islands ◽  
Mineral Deposit ◽  
South Central ◽  
Ti Oxides ◽  
Upper Paleozoic

The upper Paleozoic Fennell Formation in south-central British Columbia consists of basalts and associated marine sediments metamorphosed at low greenschist facies conditions. Although the microphenocrysts of plagioclase and Fe–Ti oxides are almost completely altered, those of augite and amphibole have survived this metamorphism. In the vicinity of the Chu Chua mineral deposit, relict augite microphenocrysts, which constitute a major proportion of the microphenocryst assemblage, are enriched in Al and Ti and are similar in composition to those from alkalic and transitional basalts. Relict amphiboles are also enriched in Ti (4.5–5.9% TiO2) and are classified as kaersutites. The occurrence of kaersutite and the chemistry of relict augites indicate that in this area the Fennell Formation basalts were originally alkalic and transitional in composition. On conventional Ti–(Zr/P2O5) and (Nb/Y)–(Zr/P2O5) immobile-element discrimination diagrams, both the kaersutite-bearing and kaersutite-free rocks plot in the tholeiitic basalt field. Accordingly, it is suggested that these diagrams may not provide clear evidence for the magmatic composition of altered volcanic rocks.Based on the lead isotopic compositions, petrographic features, and alkalic character of the Fennell Formation basalts, it is interpreted that these basalts were formed in a tectonic setting similar to that of present-day oceanic islands or seamounts.

Geological and geochemical evidence for variable magmatism and tectonics in the southern Canadian Cordillera: Paleozoic to Jurassic suites, Greenwood, southern British Columbia

2001 ◽  
Vol 38 (1) ◽  
pp. 75-90 ◽  
Author(s):  
J Dostal ◽  
B N Church ◽  
T Hoy
Keyword(s):  
British Columbia ◽  
Middle Triassic ◽  
Volcanic Rocks ◽  
Sedimentary Rocks ◽  
Deep Ocean ◽  
Island Arc ◽  
Canadian Cordillera ◽  
South Central ◽  
Upper Paleozoic ◽  
Paleozoic Rocks

The Paleozoic and early Mesozoic rocks of the Greenwood mining camp in southern British Columbia are a part of the Quesnel terrane in the eastern part of the Intermontane Belt of the Canadian Cordillera. Upper Paleozoic rocks include the Knob Hill Group composed of oceanic tholeiitic basalts (with (La/Yb)n [Formula: see text] 0.4–1.2), associated with deep ocean sedimentary rocks and serpentinites; the Attwood Group that comprises island-arc tholeiites (with (La/Yb)n [Formula: see text] 1–4 and positive εNd values), clastic sedimentary rocks and limestones; and a unit of oceanic gabbros with (La/Yb)n < 0.5. These lithologically defined units occur as tectonically emplaced slivers of oceanic crust probably produced during the closure of the Slide Mountain basin during the Permian. They are unconformably overlain by Middle Triassic calc-alkaline volcanic and sedimentary rocks of the Brooklyn Group. The Brooklyn Group volcanic rocks have characteristics of mature island-arc rocks, including (La/Yb)n [Formula: see text] 2.5–4.5 and positive εNd values. The Paleozoic rocks are crosscut by a 200 million years old granodioritic intrusion containing zircon with an Early Proterozoic inheritance age (~2.4 Ga). By inference, southern Quesnellia may have been well offshore from the ancestral North American margin in the Mississippian, in close proximity to the margin by the Middle Triassic, and contiguous with it by the Early Jurassic. It is suggested that the complex tectonic history of extension and contraction of the southern Canadian Cordillera during the post Middle Jurassic can be extended in south-central British Columbia as far back as the upper Paleozoic.

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