Detrital record of the Gravina arc, southeastern Alaska: Petrology and provenance of Seymour Canal Formation sandstones

Cohen, Harvey A.; Lundberg, Neil

doi:10.1130/0016-7606(1993)105<1400:drotga>2.3.co;2

Cited by 38 publications

(35 citation statements)

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“…The petrology of volcanic (Berg et al, 1972;Rubin and Saleeby, 1991;McClelland et al, 1991b;Stowell et al, this volume) and sedimentary rocks (Cohen, 1992) in the Gravina belt suggests an arc environment with a marine basin on the eastern side of the arc (Fig. 15A) (Cohen and Lundberg, 1993). Rubin et al (1990), McClelland et al (1992), and van der Heyden (1992) suggested that the Insular and Intermontane terranes were amalgamated prior to deposition of the Gravina belt.…”

Section: Discussion and Synthesismentioning

confidence: 96%

Metamorphic history of the Coast Mountains orogen, western British Columbia and southeastern Alaska

Stowell¹,

Crawford²

2000

Tectonics of the Coast Mountains, Southeastern Alaska and British Columbia

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The northern Coast Mountains are underlain by the Coast Plutonic Complex, which separates the Intermontane and Insular superterranes. Syndeformational contact and regional metamorphism associated with compressional and transpressional tectonic events occurred from about 101 to 50 Ma, followed by contact metamorphism adjacent to late Oligocene and Miocene plutons and stocks. Metamorphic events comprise pre-101 Ma regional metamorphism (M R 1 ), 101-90 Ma contact metamorphism (M C 2 ) and related regional metamorphism (M R 2 ), 90-85 Ma regional metamorphism (M R 3 ) that formed during thrusting that inverted metamorphic isograds, and 72-50 Ma contact and regional metamorphism (M C 4 -R ) in the central part of the orogen. Middle to Late Cretaceous moderate-to high-pressure metamorphic assemblages in the western metamorphic belt record tectonic burial and subsequent exhumation. Late Cretaceous to Tertiary sillimanite-zone metamorphic assemblages in the central pluton gneiss and the adjacent edge of the western metamorphic belt record emplacement and subsequent exhumation of plutons in the Paleogene Coast Mountains batholith, including Coast Plutonic Complex sill plutons. The final metamorphic event was ca. 25-20 Ma contact metamorphism (M C 5 ) associated with gabbroic and granitic plutons.

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Section: Discussion and Synthesismentioning

confidence: 96%

Metamorphic history of the Coast Mountains orogen, western British Columbia and southeastern Alaska

Stowell¹,

Crawford²

2000

Tectonics of the Coast Mountains, Southeastern Alaska and British Columbia

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“…Although contacts between the Gravina belt and adjacent rocks are poorly exposed, the belt probably onlaps the adjacent terranes (Brew and Karl, 1988). Sedimentary facies and the nature of volcanic rocks have led to interpretations that the Gravina belt represents a basinal arc (Berg et al, 1972), an intraoceanic arc constructed on the older Alexander terrane (Cohen and Lundberg, 1993), or an intraarc rift (van der Heyden, 1992).…”

Section: Gravina Beltmentioning

confidence: 96%

Geochemistry and tectonic setting of basaltic volcanism, northern Coast Mountains, southeastern Alaska

Stowell¹,

Green²,

Hooper³

2000

Tectonics of the Coast Mountains, Southeastern Alaska and British Columbia

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Subgreenschist to amphibolite facies metavolcanic rocks found along the western flank of the Coast Plutonic Complex (western metamorphic belt) between Berners Bayand Endicott Arm, southeastern Alaska, are divided into three distinct sequences on the basis of age and the nature of interbedded metasedimentary rocks. These sequences crop out in linear belts, from west to east: the Gravina belt of Jurassic-Cretaceous age, the western Taku terrane of Permian to Triassic age, and the eastern Taku-YukonTanana terrane of largely unknown age. Major, minor, trace element, and relict phenocryst chemistry are used to locate boundaries between the sequences and to provide clues to their origin. Variations in large ion lithophile element (LILE) and high field strength element (HFSE) abundances indicate that Gravina and eastern Taku magmas were derived through subduction-related processes. Pyroxene phenocryst compositions, LILE, light rare earth element, and HFSE enrichments in Gravina belt rocks are suggestive of high-K calc-alkaline to shoshonitic magmatism. Amphibolite facies metavolcanic rocks in the eastern Taku terrane are inferred to be island arc tholeiites. Western Taku metavolcanic rocks show little or no evidence of subduction-related genesis and resemble within-plate, possibly plume-related, basaltic magmas.Tectonic settings and magma sources inferred from metabasalt geochemistry and the associated stratigraphy of the three sequences are compatible with derivation of all the volcanic rocks in the western metamorphic belt and the Wrangellia terrane from a single Permian to Cretaceous arc complex. Initiation of arc tholeiite volcanism in the eastern Taku terrane possibly occurred during or prior to the Permian. Correlation of western Taku and Wrangellia rocks suggests a Triassic link between the Alexander and at least part of the Taku terrane, and nonsubduction-related basaltic volcanism prior to the Late Jurassic. Later rifting and/or changes in subduction geometry may have resulted in eruption of Gravina arc lavas into a marine basin, possibly floored by western Taku-Wrangellia rocks.

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“…These characteristics, as well as the fact that these rocks overlie the presumed Alexander terrane units of the Digby sequence, suggest that the Venn sequence may correlate with Gravina sequence rocks, originally described by Berg et al (1972). Throughout their extent, Gravina belt rocks have been interpreted to depositionally overlie the Alexander terrane (Berg et al, 1972;Cohen and Lundberg, 1993). West of Prince Rupert, as is also true in southeastern Alaska, contacts are either faulted or unexposed (Brew and Karl, 1988).…”

Section: Venn Sequence (Gravina Belt?)mentioning

confidence: 96%

“…In the Ketchikan quadrangle, the Gravina sequence consists of Upper Jurassic andesite and basaltic metavolcanic and volcaniclastic rocks overlain by graded bedded metagraywacke of unknown age; farther north metagraywacke units have fossils with ages as young as Cenomanian (Cohen and Lundberg, 1993). Plagioclase, hornblende, and biotite dominate the mineral assemblage in the Gravina metagraywacke of the Ketchikan quadrangle.…”

Section: Venn Sequence (Gravina Belt?)mentioning

confidence: 99%

Terrane assembly and structural relationships in the eastern Prince Rupert Quadrangle, British Columbia

Crawford

Gehrels

2000

Tectonics of the Coast Mountains, Southeastern Alaska and British Columbia

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The eastern part of the Prince Rupert quadrangle, British Columbia, is subdivided into two regions: the western metamorphic belt and the central belt. The western metamorphic belt is underlain by five distinct mappable rock sequences. From west to east these are the Digby, Venn, Delusion Bay, Kaien, and Tsimpsean sequences. Rocks of the Digby sequence seem to correlate with Triassic and upper Paleozoic rocks of the Alexander terrane; the overlying Venn sequence contains rocks of the same age as parts of the Gravina belt. The Tsimpsean sequence is considered to be part of the Yukon-Tanana terrane, a continental margin assemblage. Correlation of the two intervening sequences, Kaien and Delusion Bay, is uncertain; they may belong either to the Taku terrane or to the Yukon-Tanana terrane. We tend to favor the latter interpretation. North-to northwest-striking thrust faults approximately bisect the belt and separate the Digby and Venn sequences on the west from the structurally overlying units to the east. Near Prince Rupert, west-directed, probably midCretaceous, thrusting accompanied emplacement of tonalite and basalt dikes and sills. These thrusts and others to the north juxtapose upper amphibolite facies rocks over greenschist facies schist. The northern thrusts appear to postdate the regional metamorphism. Above and below the thrusts the rocks show intense ductile deformation. The Prince Rupert shear zone, east of the thrusts, records a strong flattening deformation, possibly due to overthrusting by the 91 Ma Ecstall pluton and associated high-grade gneiss. This tectonic emplacement of hot rocks and the associated igneous activity represented by syntectonic tonalite sills emplaced in the shear zone are inferred to be the cause of the 90 Ma amphibolite facies metamorphism that underlies the Prince Rupert shear zone.The western metamorphic belt is bounded on the east by the Coast shear zone, which separates the western belt from the central belt. This shear zone evolved during emplacement of 65-52 Ma plutons of the Paleogene Coast Mountains batholith that underlie much of the central belt. As the Coast Mountains batholith was emplaced, strain within the arc changed from dominantly contractional normal to the batholith and to the orogen, to extensional parallel to the length of the batholith. The latter stages of batholith emplacement apparently accompanied batholith exhumation. The youngest part of the Coast shear zone is a 1-2-km-wide zone of vertical fabric along the western side of the shear zone and is at the westernmost extent of 85-50 Ma plutons. This Work-Behm shear zone formed during the late stages of uplift of the western metamorphic belt by westward tilting about a northwest-trending hinge. After a hiatus with no identified tectonic activity other than gradual exhumation, Miocene and younger felsic and mafic dikes and young brittle faults cut the rocks throughout the eastern part of the quadrangle.

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Detrital record of the Gravina arc, southeastern Alaska: Petrology and provenance of Seymour Canal Formation sandstones

Cited by 38 publications

References 0 publications

Metamorphic history of the Coast Mountains orogen, western British Columbia and southeastern Alaska

Metamorphic history of the Coast Mountains orogen, western British Columbia and southeastern Alaska

Geochemistry and tectonic setting of basaltic volcanism, northern Coast Mountains, southeastern Alaska

Terrane assembly and structural relationships in the eastern Prince Rupert Quadrangle, British Columbia

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