Eastern Margin of the Central Gneiss Complex in the Shames River area, Terrace, British Columbia

Three major phases of folding affected rocks of Late Proterozoic and Early Paleozoic age and members long assigned to the Shuswap Complex of southeastern British Columbia. The main and first phase of folding produced a large recumbent anticline, having a northerly trend, overturned to the east, that contains an exotic wedge of granite-gneiss within its core. This gneiss was mechanically emplaced into the Late Proterozoic and Early Paleozoic sediments, and already had a metamorphic and deformational history prior to its emplacement. Its age is possible Hudsonian equivalent. Metamorphism during this recumbent phase of folding was greenschist facies.Phase 2 folding was accompanied by amphibolite facies metamorphism, and caused refolding of the earlier composite recumbent anticline into open folds along southeasterly axes.A third and final phase of folding, associated with waning metamorphism, gave rise to folds along southeasterly striking axial-planes that dip steeply to the northeast. Thus, phase three folds caused tightening-up of the previously formed folds.The absolute age of these deformations is not yet known, but the Shuswap Complex, at its eastern margin, is shown to include Paleozoic rocks and some older gneisses, possibly of Hudsonian age.

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Biochronology of selected Bowser Basin strata; tectonic significance

Canadian Journal of Earth Sciences ◽

10.1139/e88-150 ◽

1988 ◽

Vol 25 (10) ◽

pp. 1571-1578 ◽

Cited By ~ 4

Author(s):

I. W. Moffat ◽

R. M. Bustin ◽

G. E. Rouse

Keyword(s):

British Columbia ◽

Late Jurassic ◽

Plant Succession ◽

Fossil Plant ◽

North Central ◽

Eastern Margin ◽

Time Period ◽

Tectonic Significance ◽

Age Range ◽

Recent Evaluation

Recent evaluation and reinterpretation of fossil floral and faunal data more clearly define the ages of strata exposed in the Groundhog Coalfield and the surrounding Bowser Basin of north-central British Columbia. In the Groundhog Coalfield, Bowser Lake Group strata consist of an overall coarsening-upwards cycle divisible into four informal stratigraphic units, which are, from oldest to youngest, the Jackson, Currier, McEvoy, and Devils Claw units. The section has an unconformable relationship with underlying Bajocian Spatsizi marine shales, volcanics, and arenaceous sediments. Marine macrofossils indicate a Callovian to Oxfordian age for the Jackson unit. The fossil plant succession present in the overlying Currier unit indicates Late Jurassic affinities. Recent unpublished palynologic data from lower McEvoy rocks in the northern Groundhog Coalfield suggest a Barremian age. The palynoassemblage present in the lower Devils Claw unit in the central part of the Groundhog Coalfield suggests a late middle Albian age.Rocks of the Sustut Group have an angular unconformable relationship with underlying Bowser Lake Group strata near the eastern margin of the Bowser Basin. The palynoassemblage present in Sustut Group rocks from the southern Sustut Basin suggests a Campanian to Maastrichtian age range, in contrast to a probable late Albian to Campanian age range for the northern Sustut Basin and a middle to late Albian age from Sustut Group outliers present within the northern Bowser Basin. Within the Groundhog Coalfield, Devils Claw strata have a conformable or paraconformable relationship with underlying Bowser Lake Group strata.Regional discrepancy in the age and geometry of the sub-Sustut unconformity is attributed to a time-transgressive unconformity that resulted from cratonward advance of an isostatically induced peripheral bulge. Age and contact relationships suggest that deformation in the Bowser Basin and surrounding Sustut Basin must have spanned the time period that corresponds to a second uplift pulse of the Columbian orogen (Aptian to early Cenomanian) and the uplift pulse related to the Laramide orogen (Campanian to Maastrichtian).

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Geochronometry of the Eagle Plutonic Complex and the Coquihalla area, southwestern British Columbia

Canadian Journal of Earth Sciences ◽

10.1139/e92-068 ◽

1992 ◽

Vol 29 (4) ◽

pp. 812-829 ◽

Cited By ~ 15

Author(s):

C. J. Greig ◽

R. L. Armstrong ◽

J. E. Harakal ◽

D. Runkle ◽

P. van der Heyden

Keyword(s):

British Columbia ◽

Late Jurassic ◽

Middle Eocene ◽

Timing Constraints ◽

Early Eocene ◽

East Side ◽

Eastern Margin ◽

Plutonic Complex ◽

Southwestern Margin

New U–Pb, K–Ar, and Rb–Sr dates from the Eagle Plutonic Complex and adjacent map units place timing constraints on intrusive and deformational events along the southwestern margin of the Intermontane Belt. U–Pb zircon minimum dates for Eagle tonalite and gneiss (148 ± 6, 156 ± 4, and 157 ± 4 Ma) document previously unrecognized Middle to Late Jurassic magmatism and syn-intrusive deformation along the eastern margin of the Eagle Plutonic Complex and the southwestern margin of the Intermontane terrane. Widespread mid-Cretaceous (Albian–Cenomanian) resetting of K–Ar and Rb–Sr isotopic systematics in Jurassic and older rocks is coeval and cogenetic with emplacement of plutons of the Fallslake Plutonic Suite (110.5 ± 2 Ma, U–Pb) which crosscut Jurassic plutons and structures but were themselves ductilely deformed along the Pasayten fault during sinistral, east-side-up, reverse displacement. K–Ar and Rb–Sr cooling dates for the Fallslake Suite of ca. 100 Ma, including dates from mylonites along the Pasayten fault, suggest that uplift, cooling, and unroofing of the Eagle Plutonic Complex occurred in mid-Cretaceous time along the Pasayten fault. Regional geologic evidence suggests that this thermal and unroofing event affected much of the southwest margin of the Intermontane Belt. Initial 87Sr/86Sr ratios and U–Pb geochronometry for the Fallslake Plutonic Suite suggest that it was derived, in part, from preexisting and relatively nonradiogenic Paleozoic to Mesozoic crust. K–Ar dating of several stocks demonstrates widespread Early Eocene plutonism in the Coquihalla area, and dating of the Needle Peak pluton indicates plutonism continued into Middle Eocene time.

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ZIRCON U-PB CONSTRAINTS ON THE AGES AND OBSCURED BOUNDARIES OF TERRANES IN THE WESTERN NORTH AMERICAN CORDILLERA: CENTRAL GNEISS COMPLEX, BRITISH COLUMBIA

10.1130/abs/2018ne-311042 ◽

2018 ◽

Author(s):

Douglas R. MacLeod ◽

◽

David M. Pearson ◽

David M. Pearson

Keyword(s):

British Columbia ◽

North American ◽

Cordillera Central ◽

North American Cordillera ◽

Gneiss Complex

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Ductile shearing and brittle faulting in Valhalla gneiss complex, southeastern British Columbia

10.4095/120029 ◽

1985 ◽

Cited By ~ 3

Author(s):

S D Carr

Keyword(s):

British Columbia ◽

Gneiss Complex ◽

Ductile Shearing ◽

Brittle Faulting

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Very high temperature, moderate pressure metamorphism in the New Russia gneiss complex, northeastern Adirondack Highlands, metamorphic aureole to the Marcy anorthosite

Canadian Journal of Earth Sciences ◽

10.1139/e98-072 ◽

1999 ◽

Vol 36 (1) ◽

pp. 1-13 ◽

Cited By ~ 3

Author(s):

J Alcock ◽

Peter Muller

Keyword(s):

New York ◽

High Temperature ◽

Moderate Pressure ◽

Dehydration Melting ◽

Eastern Margin ◽

Gneiss Complex ◽

Anorthosite Massif ◽

Metamorphic Gradient ◽

High Temperature Metamorphism ◽

Very High

The New Russia gneiss complex in the northeastern Adirondack Highlands of New York includes meta-anorthosite gneiss and anatectic gneiss derived from metagabbro, mangerite, and charnockite. Metamorphic conditions during anatexis (850-950°C, highest near the anorthosite, with pressure ~750 MPa) are inferred from minerals and textures produced by dehydration melting of pargasitic hornblende and from ternary feldspar in anatectic segregations. The complex abuts and is crosscut by the eastern margin of the ~1130 Ma Marcy anorthosite massif. The crosscutting contact, the presence of meta-anorthosite gneiss within the complex and undeformed meta-anorthosite in the massif, and the occurrence of deformed and undeformed anatectic segregations within the New Russia gneisses indicate an approximate synchroneity of penetrative deformation, very high temperature metamorphism, and emplacement of anorthosite with both intrusion and anatexis outlasting deformation. The position of the New Russia gneisses, the metamorphic gradient within them, and the contemporaneity of anatexis with intrusion of anorthosite imply that the complex is the metamorphic aureole of the Marcy anorthosite.

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