scholarly journals The age of the Mount Copeland Syenite Gneiss and its metamorphic zircons, Monashee Complex, southeastern British Columbia

1988 ◽  
Author(s):  
R R Parrish ◽  
R J Scammell
Keyword(s):  
British Columbia ◽  
Monashee Complex

P–T history and kinematics of the Monashee Décollement near Revelstoke, British Columbia

1989 ◽  
Vol 26 (2) ◽  
pp. 231-243 ◽  
Author(s):  
Larry S. Lane ◽  
Edward D. Ghent ◽  
Mavis Z. Stout ◽  
Richard L. Brown
Keyword(s):  
British Columbia ◽  
Shear Band ◽  
Late Cretaceous ◽  
Hanging Wall ◽  
Multiple Criteria ◽  
Early Eocene ◽  
Kinematic Indicators ◽  
Metamorphic Assemblage ◽  
Monashee Complex

Microstructural and petrofabric analyses of mylonites from the Monashee Décollement demonstrate that the hanging wall was displaced eastward over the footwall. Microstructural kinematic indicators include shear-band foliation, asymmetric strain shadows, and S–C fabrics. Quartz c axes locally exhibit asymmetric fabrics that are consistent with the microstructural evidence for sense of shear. The kinematic evidence is reliable because multiple criteria coexist within individual specimens.Metamorphic assemblages from footwall Monashee Complex pelites at the Revelstoke damsite indicate that the peak metamorphic assemblage was sillimanite–K-feldspar–biotite–almandine–quartz ± plagioclase. Biotite–garnet geothermometry and garnet–plagioclase–sillimanite–quartz geobarometry set broad constraints on metamorphic temperatures but closer constraints on pressures, near 650 °C and 630 MPa.Comparison of these data with Late Cretaceous hornblende cooling ages from the same locality indicates that the metamorphism is at least as old as Late Cretaceous. Complex microstructures relating to repeated mylonitization and annealing render difficult the correlation of metamorphic conditions with mylonitic fabrics. Early mylonitic textures predate the metamorphic equilibration and thus are pre-Late Cretaceous in age. Postmetamorphic mylonites are well preserved, but their ages are poorly constrained. The present interpretation favours a Late Cretaceous to Paleocene age relating to compressional tectonics. However, an Early Eocene age relating to extensional shearing cannot be excluded.

Paleozoic plutonism in southeastern British Columbia

1985 ◽  
Vol 22 (10) ◽  
pp. 1409-1424 ◽  
Author(s):  
Andrew V. Okulitch
Keyword(s):  
British Columbia ◽  
Clear Relationship ◽  
Granitic Gneiss ◽  
Granitoid Pluton ◽  
Quartz Monzonite ◽  
Monashee Complex ◽  
Devonian Age ◽  
Tectonic Slice ◽  
Affected Country ◽  
Made In

U–Pb dates from zircons indicate that plutonic events occurred during the Paleozoic in the Omineca Crystalline Belt in southeastern British Columbia. In the Kootenay Arc, granitoid cobbles in conglomerate of the Carboniferous Milford Group were derived from quartz monzonite and diorite plutons of probable Ordovician age. Near Little Shuswap Lake, gneissic granitoid units have yielded Cambro-Ordovician ages. At least one episode of deformation affected country rocks of unknown age before intrusion. In the Monashee Complex south of Thor–Odin Nappe in South Fosthall Creek, lineated quartz monzonite is of probable Ordovician age. Comparison of fabrics suggests that at least one episode of metamorphism and deformation occurred prior to intrusion. No clear relationship between the cobbles and these plutons can be demonstrated because major faults lie between them, but substantial revision to accepted models of Paleozoic paleogeography of this region will have to be made. In the Clachnaeudainn tectonic slice east of the Monashee Complex, granitic gneiss is of Paleozoic, possibly Siluro-Devonian, age. This pluton appears to be involved in all phases of deformation that affected its country rocks. Near Quesnel Lake, parts of a composite gneissic granitoid pluton appear to be of Devonian or earliest Carboniferous age.

Significance of a Cambrian date from galena lead-isotope data for the stratiform Cottonbelt deposit in the Monashee Complex, southeastern British Columbia

1988 ◽  
Vol 25 (9) ◽  
pp. 1534-1541 ◽  
Author(s):  
T. Höy ◽  
C. I. Godwin
Keyword(s):  
British Columbia ◽  
Isotope Ratio ◽  
Lead Isotope ◽  
Yukon Territory ◽  
Lower Paleozoic ◽  
Magnetite Layer ◽  
Monashee Complex ◽  
Selkirk Mountains ◽  
Lead Zinc ◽  
Isotope Analyses

The Cottonbelt deposit is a large stratiform lead–zinc–magnetite layer within cover rocks of Frenchman Cap dome in the Monashee Complex in southeastern British Columbia. Lead-isotope analyses of galena samples from the deposit plot close to the Cambrian–Hadrynian boundary on lead-isotope ratio diagrams and are similar to analyses of Early Cambrian stratiform deposits in the Anvil Camp in the Yukon Territory. These data suggest that the Cottonbelt deposit and host succession are Cambrian in age, in contrast to other interpretations that suggest considerably older ages for the cover succession of Frenchman Cap dome. These cover rocks, therefore, are considered calcareous and pelitic facies of lower Paleozoic shelf rocks now exposed in the Kootenay Arc to the southeast and the Selkirk Mountains to the east.

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