The western margin of the Coast Plutonic Complex on Hardwicke and West Thurlow Islands, British Columbia

1979 ◽  
Vol 16 (6) ◽  
pp. 1166-1175 ◽  
Author(s):  
Jo Anne Nelson
Keyword(s):  
Quartz Diorite ◽  
Contact Metamorphism ◽  
Contact Aureole ◽  
Western Margin ◽  
Late Mesozoic ◽  
The North ◽  
Early Mesozoic ◽  
Plutonic Complex ◽  
Coast Plutonic Complex ◽  
Maximum Contact

The western margin of the Coast Plutonic Complex, one of the major tectonic boundaries of the Canadian Cordillera, has been variously interpreted as an intrusive contact, a shear zone, and a suture zone joining the Early Mesozoic Insular Belt to the North American continent. A representative section of this boundary, exposed on islands in Johnstone Strait, is an intrusive contact along which a quartz diorite with peripheral mafic phases truncates Early Mesozoic sediments and volcanics of the Insular Belt. Concordant hornblende–biotite pairs and two whole rock biotite isochrons date the intrusion as Late Jurassic (151 Ma). Prior to intrusion the stratified units underwent prehnite–pumpellyite facies metamorphism and west-northwest block faulting.The contact aureole of the quartz diorite and its associated mafic phases involves greenschist and hornblende–hornfels facies assemblages. Total pressure in the upper Karmutsen Formation during contact metamorphism was less than 2.5 × 105 kPa. The maximum contact temperature was between 670 and 700 °C. Forcible emplacement of the intrusion caused penetrative deformation of wall rocks in the inner aureole. The maximum contact temperatures indicate that the plutonic bodies were at near-liquidus temperatures when emplaced.The contact on Hardwicke and West Thurlow Islands appears representative of most of the tectonic boundary between the southern Coast Plutonic Complex and the Insular Belt. The western margin of the Coast Plutonic Complex is thus a Late Mesozoic magmatic front, the western limit of the intense magmatism that generated the Coast Plutonic Complex. The formation of Georgia Depression over the province boundary was a later event, coeval with major uplift of the Coast Plutonic Complex.

Rb/Sr Ages and a profile of initial Sr87/Sr86 ratios for plutonic rocks across the Yukon Crystalline Terrane

1976 ◽  
Vol 13 (2) ◽  
pp. 319-330 ◽  
Author(s):  
P. C. Le Couteur ◽  
D. J. Tempelman-Kluit
Keyword(s):  
Quartz Diorite ◽  
Igneous Rocks ◽  
Slow Cooling ◽  
Precambrian Rocks ◽  
Quartz Monzonite ◽  
Plutonic Complex ◽  
Coast Plutonic Complex ◽  
Plutonic Rocks

Nine Rb/Sr apparent ages are reported for igneous rocks of the Yukon Crystalline Terrane. The oldest age (144 m.y.) is from the Triassic? Klotassin quartz diorite and is thought to be a hybrid age that probably reflects the effects of younger intrusives on rocks at least 190 m.y. old. Five ages of about 100 m.y. presumably reflect the cooling of the Coffee Creek quartz monzonite. K/Ar ages for this event are slightly younger than the Rb/Sr ages, suggesting slow cooling. Rb/Sr ages of 53 and 67 m.y. were obtained for the Ruby Range batholith and an age of 61–67 m.y. for the Nisling Range alaskite. The Rb/Sr ages obtained generally confirm recently determined K/Ar ages. There is a regional decrease in initial Sr87/Sr86 ratios, southwestward across the Yukon Crystalline Terrane. This may mean that Precambrian rocks extend under the Yukon Crystalline Terrane, but are absent under the adjoining Coast Plutonic Complex.

Distribution and tectonic significance of Upper Triassic terranes in the eastern Coast Mountains and adjacent Intermontane Belt, British Columbia

1991 ◽  
Vol 28 (4) ◽  
pp. 532-541 ◽  
Author(s):  
Margaret E. Rusmore ◽  
G. J. Woodsworth
Keyword(s):  
Upper Triassic ◽  
Eastern Coast ◽  
Coast Mountains ◽  
Early Mesozoic ◽  
Tectonic Significance ◽  
Plutonic Complex ◽  
Coast Plutonic Complex ◽  
Basalt Geochemistry ◽  
Volcaniclastic Rocks ◽  
Final Closure

New data on Upper Triassic rocks in the eastern Coast Mountains show that it is Stikinia, not Wrangellia, that lies along the eastern margin of the Coast Plutonic Complex, at least as far south as latitude 51°N. These rocks constitute the upper Carnian–lower Norian Mt. Moore formation and the upper Norian Mosley formation. Clinopyroxene-phyric basaltic to andesitic breccia with lesser volcanic sandstone and rare carbonate compose the Mt. Moore formation. The Mosley formation comprises mafic volcaniclastic rocks and limestone. Correlation of these formations with Stikinia is based on similarities in age, stratigraphy, lithology, basalt geochemistry, and inferred tectonic setting.Recognition of Upper Triassic arc-related rocks of the Cadwallader terrane east of its previously known extent indicates that the Cadwallader terrane, rather than Stikinia, underlies much of the southern Intermontane Belt. The revised terrane distribution shows that Stikinia lay west of both the Cadwallader and Bridge River terranes prior to Cretaceous and Tertiary faulting. This configuration supports the idea that the Cadwallader and Stikine terranes represent fragments of a single early Mesozoic arc that was accreted during final closure of the Cache Creek – Bridge River ocean in Middle Jurassic time.

Interpretation of isotopic ages and 87Sr/86Sr initial ratios for plutonic rocks in the Whitehorse map area, Yukon

1979 ◽  
Vol 16 (10) ◽  
pp. 1988-1997 ◽  
Author(s):  
Gregg W. Morrison ◽  
Colin I. Godwin ◽  
Richard L. Armstrong
Keyword(s):  
British Columbia ◽  
Oceanic Crust ◽  
Late Cretaceous ◽  
Canadian Cordillera ◽  
Initial Ratio ◽  
Eastern Margin ◽  
The North ◽  
Plutonic Complex ◽  
Coast Plutonic Complex ◽  
North American Craton

Sixteen new K–Ar dates and four new Rb–Sr isochrons help define four plutonic suites in the Whitehorse map area, Yukon. The Triassic(?) suite, defined on stratigraphic evidence, is the southern extension of the Yukon Crystalline Terrane and is correlative with plutonic suites in the Intermontane Belt in British Columbia. The mid-Cretaceous (~100 Ma) suite in the Intermontane Belt in the Whitehorse map area is time equivalent to plutonic suites in the Omineca Crystalline Belt to the east. Late Cretaceous (~70 Ma) and Eocene (~55 Ma) suites include volcanic and subvolcanic as well as plutonic phases and are correlative with continental volcano–plutonic suites near the eastern margin of the Coast Plutonic Complex. The predominance of the mid-Cretaceous suite in the Intermontane Belt in Whitehorse and adjacent map areas in Yukon and northern British Columbia suggests that this area has undergone posttectonic magmatism more characteristic of the Omineca Crystalline Belt than of the Intermontane Belt elsewhere in the Canadian Cordillera.87Sr/86Sr initial ratio determinations suggest that the southern extension of the Yukon Crystalline Terrane in the western part of the Whitehorse map area and in northern British Columbia includes Precambrian crust separated from the North American craton by Paleozoic oceanic crust of the Intermontane Belt.

Paleomagnetism of Mesozoic plutons in the westernmost Coast Complex of British Columbia

1977 ◽  
Vol 14 (9) ◽  
pp. 2127-2139 ◽  
Author(s):  
D. T. A. Symons
Keyword(s):  
North American ◽  
Leading Edge ◽  
Upper Jurassic ◽  
North American Plate ◽  
The North ◽  
Banks Island ◽  
Plutonic Complex ◽  
Normal Polarity ◽  
Coast Plutonic Complex ◽  
North American Craton

The Lower Cretaceous Stephens Island (102 ± 8 Ma) and Captain Cove (109 ± 6 Ma) plutons and the Upper Jurassic Gil Island (136 ± 3 Ma) and Banks Island (144 ± 6 Ma) plutons belong to the western K–Ar age zone of the N 35° W trending Coast plutonic complex southwest of Prince Rupert, B.C. After removal of initial viscous components, AF demagnetization isolates a stable primary remanence at 36 of 49 sites (10 specimens from 5 cores/site) before anhysteretic components are added. All sites have normal polarity which is consistent because their K–Ar ages fall in the predominantly normal Cretaceous and Jurassic Quiet Intervals. The poles for Stephens Island (339° W, 67° N (7°, 10°)), Captain Cove (9° W 72° N (8°, 11°)), and Gil Island (357° N. 70° N (6°, 8°)) lie just north of Britain and are discordant for the North American craton. The tectonic panel including these plutons was tilted [Formula: see text] during the Upper Cretaceous–Paleocene orogeny as the leading edge of the North American plate overrode the subducting oceanic Kula Plate. This interpretation is supported by other arguments including the attitudes of contacts and foliations, plutonic trend directions, distribution of metamorphic grades, and paleomagnetic data from the area to the east. The Banks Island pluton lies in the tectonic panel to the west. Its pole of 210° W, 81° N (33°, 38°) is poorly defined but apparently concordant.

scholarly journals Intrusion history of the Portrush Sill, County Antrim, Northern Ireland: evidence for rapid emplacement and high-temperature contact metamorphism

2011 ◽  
Vol 149 (1) ◽  
pp. 67-79 ◽  
Author(s):  
MORGANE LEDEVIN ◽  
NICHOLAS ARNDT ◽  
MARK R. COOPER ◽  
GARTH EARLS ◽  
PAUL LYLE ◽  
...  
Keyword(s):  
Northern Ireland ◽  
Sedimentary Rocks ◽  
Lower Jurassic ◽  
Contact Metamorphism ◽  
Geochemical Data ◽  
Contact Aureole ◽  
The North ◽  
Geochemical Analyses ◽  
Element Enrichment ◽  
County Antrim

AbstractThe gabbroic Portrush Sill in Northern Ireland, part of the North Atlantic Igneous Province, intruded Lower Jurassic mudstones and siltstones about 55 Ma ago. We used petrologic observations and geochemical analyses to study how the sill interacted with the sedimentary rocks. Field relationships show that an Upper Sill and numerous associated Minor Intrusions were emplaced in the sedimentary host rocks before intrusion of the Main Sill, some 10 m above its upper contact. Geochemical analyses reveal two magma contamination processes: Nb and Ta anomalies, coupled with incompatible element enrichment, record contamination by deep crustal rocks, whereas Li, Pb and Ba anomalies reveal a superficial contamination through fluid circulation at the contact between magmatic and sedimentary rocks. Analysis of mineral assemblages and geochemical data from the contact aureole demonstrate uniform metamorphic conditions between the two main intrusions and an absence of a thermal gradient. The identification of pyrrhotite by magnetization analyses and of orthopyroxene by microprobe analyses indicates very high temperatures, up to 660°C. Thermal modelling explains these temperatures as the coupled effects of the Main Sill and the earlier intruded Upper Sill and Minor Intrusions. Even though the chemical composition of the Main Sill suggests another type of parental liquid, all three units were emplaced in a very short time, certainly less than five years.

Chronology of Cadomian tectonothermal activity in the baie de Saint-Brieuc (north Brittany), France: evidence from 40Ar/39Ar mineral ages

1991 ◽  
Vol 28 (5) ◽  
pp. 762-773 ◽  
Author(s):  
R. D. Dallmeyer ◽  
R. A. Strachan ◽  
R. S. D'Lemos
Keyword(s):  
West African ◽  
Quartz Diorite ◽  
Contact Aureole ◽  
Metasedimentary Rocks ◽  
Late Precambrian ◽  
The North ◽  
Granite Emplacement ◽  
Continental Arc ◽  
Armorican Massif ◽  
Isotope Correlation

The late Precambrian Cadomian Orogen exposed in the North Armorican Massif (northwest France) is a collage of displaced terranes that, in part, developed during amalgamation of continental-arc and marginal-basin complexes. 40Ar/39Ar mineral ages reported here place new constraints on the timing of Cadomian tectonothermal activity in the southern part of the St Brieuc terrane. In the baie de Saint-Brieuc area Brioverian supracrustal units were deformed, metamorphosed, and intruded by calc-alkaline plutonic complexes. Metamorphic hornblende from a metabasic amphibolite sheet within Brioverian rocks records an isotope correlation age of 568.4 ± 2.6 Ma (interpreted to date postmetamorphic cooling through appropriate argon closure temperatures). Similar isotope correlation cooling ages are recorded by metamorphic hornblende within both an amphibolite sheet intrusive into the Penthièvre complex (567.5 ± 1.2 Ma) and the La Croix Gibat amphibolite (574.8 ± 2.1 Ma). Igneous hornblende from the late tectonic to posttectonic St Quay quartz diorite and muscovite from Brioverian metasedimentary rocks in the contact aureole record isotope correlation ages of ca. 565–570 Ma. These and a ca. 568 Ma isotope correlation age determined for hornblende from the foliated Fort de la Latte quartz diorite are interpreted to date postmagmatic cooling.The 40Ar/39Ar ages indicate that Cadomian tectonothermal activity within southern parts of the St Brieuc terrane occurred prior to ca. 570 Ma. This is markedly older than the ca. 540 Ma date previously suggested for peak Cadomian metamorphism and granite emplacement in the adjacent St Malo terrane and is consistent with palinspastic separation of the contrasting Cadomian elements until at least the latest Precambrian. A pre-570 Ma age for Cadomian tectonothermal activity in the St Brieuc terrane suggests correlation with similar-aged orogenic activity in other circum-Atlantic, late Precambrian Gondwanan marginal terranes (including southern portions of the Iberian massif and various sectors of the West African orogens).

The Scotia–Quaal metamorphic belt: a distinct assemblage with pre- early Late Cretaceous deformational and metamorphic history, Coast Plutonic Complex, British Columbia

1991 ◽  
Vol 28 (6) ◽  
pp. 870-880 ◽  
Author(s):  
S. A. Gareau
Keyword(s):  
Late Cretaceous ◽  
Middle Devonian ◽  
Regional Metamorphism ◽  
Early Jurassic ◽  
Contact Metamorphism ◽  
Metamorphic Belt ◽  
Metamorphic History ◽  
Plutonic Complex ◽  
Coast Plutonic Complex ◽  
Early Late

The Scotia–Quaal metamorphic belt extends from Hawkesbury Island to Work Channel between the early Late Cretaceous Ecstall and the Paleogene Quottoon plutons. The belt consists of a Proterozoic?–Paleozoic metasedimentary and metavolcanic sequence, the Middle Devonian Big Falls orthogneiss, Early Jurassic orthogneiss, and Jurassic or Cretaceous mafic and ultramafic intrusive rocks. The assemblage may be correlative with Nisling terrane lithologies and may have shared a common history, at least from Early Jurassic time on, with rocks of Stikine terrane.Strong planar and linear fabrics, abundant folds, and scarcity of kinematic indicators characterize the belt's deformational style. Development of a strong foliation followed by three episodes of folding occurred between emplacement of the Middle Devonian Big Falls orthogneiss and early Late Cretaceous Ecstall intrusion. Paleogene fabrics occur in the Quottoon pluton and in the easternmost 1.5 km of the Scotia-Quaal belt. If a major Paleogene shear zone is postulated to explain the disparity in cooling dates, metamorphic histories, and structural styles between the western and central Coast Plutonic Complex, then it does not traverse the Scotia–Quaal metamorphic belt, but must be located within or at the western edge of the Quottoon pluton.Medium-pressure, epidote–amphibolite to upper amphibolite facies metamorphic conditions are preserved in the central region. Metamorphic grade increases gradually across the belt from west to east and from south to north. Regional metamorphism outlasted regional deformation. Contact metamorphism associated with Quottoon and Ecstall intrusion is apparent only in rocks of the southern region where regional metamorphic grades are lowest.

Eocene rotation of the Coast Plutonic Complex and Intermontane Belt: paleomagnetism of Eocene plutons along the Klondike Highway

2011 ◽  
Vol 48 (3) ◽  
pp. 645-660 ◽  
Author(s):  
David T.A. Symons ◽  
Kazuo Kawasaki
Keyword(s):  
North America ◽  
Eastern Coast ◽  
The North ◽  
Plutonic Complex ◽  
Mixed Polarity ◽  
Thin Skin ◽  
Coast Plutonic Complex ◽  
Accreted Terranes ◽  
Tectonic Rotation ◽  
Stable Characteristic

Paleomagnetic results are reported for the ∼59 Ma Skagway, ∼54 Ma Fraser, ∼53 Ma Summit Lake, and ∼48 Ma Clifton felsic plutons of the eastern Coast Plutonic Complex (CPC) that outcrop along the south Klondike Highway in Alaska and British Columbia. Thermal and alternating field step demagnetizing methods yielded stable characteristic remanent magnetization (ChRM) directions for all 29 sites of normal, reversed, and mixed polarity. The ChRM resides in single or pseudosingle domain magnetite and (or) pyrrhotite that is shown to be primary by contact tests with the ∼47 Ma vertical White Pass mafic dikes. Paleopoles from six 56 to 50 Ma (mean 52 ± 2 Ma) Intermontane Belt – Yukon–Tanana terrane (IMB–YTT) units that cannot be explained by tectonic tilt are compared with nine clustered 59 to 46 Ma (mean 52 ± 4 Ma) eastern CPC paleopoles. Both paleopole populations show nonsignificant poleward (northward) translation relative to North America (IMB–YTT, 3.7° ± 5.3°N; CPC, 4.3° ± 6.4°S; overall, 1.2° ± 4.9°S), indicating that northward translation of the accreted terranes ended by ∼58 Ma. Conversely, both populations show clockwise (CW) rotation that is either highly significant or substantial (IMB–YTT, 19.3° ± 10.5 °CW; CPC, 7.1° ± 16.1 °CW; overall 12.8° ± 10.9 °CW). The results are best explained by tectonic rotation from ∼50 to ∼45 Ma of the IMB–YTT as a thin-skin on top of North America during emplacement and co-incident rotation of the massive Eocene plutons of the eastern CPC along the North American margin.

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