The Anvil aureole, an atypical mid-Cretaceous culmination in the northern Canadian Cordillera

1990 ◽  
Vol 27 (3) ◽  
pp. 344-356 ◽  
Author(s):  
J. M. Smith ◽  
P. Erdmer
Keyword(s):  
Country Rock ◽  
Regional Metamorphism ◽  
Volcanic Rocks ◽  
Canadian Cordillera ◽  
South Fork ◽  
Upper Proterozoic ◽  
Tectonic History ◽  
South Central ◽  
Upper Paleozoic ◽  
Peak Metamorphism

The mid-Cretaceous Anvil batholith, in south-central Yukon near Faro, intrudes Upper Proterozoic to upper Paleozoic strata of the Cordilleran outer miogeocline. From previous work, it was unclear whether biotite, andalusite–staurolite, and garnet isograds near the pluton resulted from pre-Devonian regional metamorphism and subsequent arching in a structural culmination or from mid-Cretaceous instrusion. The present study has documented biotite, andalusite, staurolite, garnet, and sillimanite isograds concentric to the pluton. Prophyroblast–matrix relationships indicate that peak metamorphism occurred during intrusion, which took place under approximately 3 kbar (300 MPa) pressure and heated country rock to temperatures of 600°–620 °C. The metamorphism is thus compatible with a deep, mid-Cretaceous event. Regional uplift of 10 km is implied by the metamorphic minerals. From cogenetic relationships between some phases of the Anvil batholith and the nearby South Fork volcanic rocks, regional uplift appears to have been completed in a few million years in the mid-Cretaceous. The uncharacteristic aureole suggests that mid-Cretaceous events in this region are atypical of the Cordillera and may reflect a unique tectonic history or position in the orogen.

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.

Distribution of Fusulinaceans in the Western Canadian Cordillera

1971 ◽  
Vol 8 (2) ◽  
pp. 259-278 ◽  
Author(s):  
J. W. H. Monger ◽  
C. A. Ross
Keyword(s):  
Volcanic Rocks ◽  
Canadian Cordillera ◽  
Crustal Movements ◽  
Clastic Rocks ◽  
Western Cordillera ◽  
Local Environments ◽  
Upper Paleozoic ◽  
Biogeographic Provinces ◽  
The Family ◽  
Part Time

Fusulinacean faunas in Upper Paleozoic lithological sequences containing volcanic rocks in the western Canadian Cordillera form two assemblages based on geographic association of genera. One assemblage, in Permian strata, is dominated by genera of the family Schwagerinidae and occupies belts in the eastern and western parts of the western Cordillera. This assemblage is associated with brachiopods, bryozoans, horn corals, and crinoids and is in limestones interbedded with clastic rocks and volcanic rocks of variable composition. The other Permian assemblage is dominated by genera of the family Verbeekinidae and occupies a central belt where it occurs with crinoid detritus and algae in thick, regionally extensive limestones associated with cherts, basalt, and ultramafic rocks. The less-well documented Pennsylvanian fusulinaceans appear to occupy similar belts. Because fossils of both assemblages are at least in part time equivalent, their distribution may well be due to differing local environments. In addition, or alternatively, this diversity may be brought about by major crustal movements juxtaposing originally isolated biogeographic provinces.

The Eocene–Oligocene magmatic hiatus in the south-central Canadian Cordillera: a capture of the Kula Plate by the Pacific Plate?

2008 ◽  
Vol 45 (1) ◽  
pp. 69-82 ◽  
Author(s):  
Jaroslav Dostal ◽  
J Duncan Keppie ◽  
B Neil Church ◽  
Peter H Reynolds ◽  
Cheryl R Reid
Keyword(s):  
Volcanic Rocks ◽  
Pacific Plate ◽  
North American Plate ◽  
Volcanic Complex ◽  
Canadian Cordillera ◽  
Continental Flood Basalts ◽  
The North ◽  
South Central ◽  
The Pacific ◽  
Back Arc

The Tertiary (Paleogene and Neogene) geological record in south-central Canadian Cordillera is dominated by the 350–400 km wide, lower Eocene volcanic arc and the overlying Miocene–Recent back-arc lavas that are separated by a hiatus in magmatic activity between 48 and 24 Ma. In the Black Dome area (~240 km north of Vancouver), the Eocene volcanic rocks are mainly continental margin calc-alkaline andesite and dacite, resulting from the melting of a juvenile mafic source at the base of the crust. In contrast, the Miocene volcanic rocks resemble continental flood basalts. Both Eocene and Miocene rocks from the Black Dome volcanic complex have high positive εNd values (+7.2 to +7.4 and +6.4 to +7.6, respectively) and low initial Sr isotopic ratios (0.702 516 – 0.703 528 and 0.703 376 – 0.703 392, respectively) comparable to modern oceanic basalts. The onset of the hiatus in magmatism at 48 Ma coincides with capture of the Kula Plate by the Pacific Plate resulting in a change in convergence direction with the North American Plate from orthogonal to margin-parallel. The margin-parallel motion is inferred to have removed a 50–100 km sliver of the Eocene forearc that formed the boundary between the Pacific and subducted Kula Plate. Reinitiation of arc magmatism at 24 Ma is related to subduction of the Farallon and associated plates and it superimposed back-arc tholeiitic magmatism on top of the Eocene arc.

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.

Late Mesozoic and Cenozoic tectonic history of south central California

Tectonics ◽  
1984 ◽  
Vol 3 (6) ◽  
pp. 659-675 ◽  
Author(s):  
A. E. J. Engel ◽  
P. A. Schultejann
Keyword(s):  
Central California ◽  
Late Mesozoic ◽  
Tectonic History ◽  
South Central ◽  
History Of

Dosage du potassium, de l'uranium, du radium et du thorium, par spectrometrie gamma dans les laves d'Auvergne, du Velay et de la province sicilienne

1963 ◽  
Vol S7-V (2) ◽  
pp. 218-231 ◽  
Author(s):  
Jean Louis Cheminee ◽  
Daniel Nordemann
Keyword(s):  
Hydrothermal Alteration ◽  
Volcanic Rocks ◽  
Statistical Dependence ◽  
Direct Proportion ◽  
Radioactive Elements ◽  
Spectrometry Analysis ◽  
Functional Relations ◽  
South Central ◽  
Intrusive Rocks ◽  
Radioactive Minerals

Abstract Fifty samples of volcanic rocks from south-central France, ranging from basalts to rhyolites, were subjected to gamma spectrometry analysis for the purpose of determining the proportions and relationships of the constituent radioactive elements. Zircon, sphene and apatite generally contained less thorium and uranium than the less abundant accessory minerals such as allanite, monazite and xenotime. Results of the analysis also show that the percentage of radioactive minerals is greater in the acidic lavas than in the intrusive rocks, suggesting that the latter were subjected to hydrothermal alteration. The percentage of potassium varies in direct proportion to the variation in the percentage of silica. The increase in thorium as a function of silica is more rapid than that of uranium. Graphically, no correlation exists between the percentage of radium and silica. The concentrations of uranium and thorium do not vary independently but seem to have a statistical dependence whose functional relations are not yet apparent.

Sign in / Sign up

Export Citation Format

Share Document