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

Crawford, María Luisa; Crawford, William A.; Gehrels, George E.

doi:10.1130/0-8137-2343-4.1

Cited by 16 publications

(15 citation statements)

References 41 publications

(85 reference statements)

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“…The tectonic affinity of these country rocks is uncertain, with possibilities including the Alexander terrane [Armstrong and Runkle, 1979], the Yukon-Tanana terrane [Crawford et al, 2000], or the Gravina belt [Gehrels, 2001]. The Prince Rupert Shear Zone dips northeast at a moderate angle along the southwestern margin of the Ecstall pluton.…”

Section: Geologic Settingmentioning

confidence: 99%

“…From regional patterns of metamorphic grade and dip of the Prince Rupert Shear Zone, it is inferred that this shear zone steepens with increasing depth in the crust. In the footwall of this thrust are Paleozoic rocks of the Alexander terrane overlain by Jura-Cretaceous strata of the Gravina belt [Woodsworth et al, 1983;Crawford et al, 1987Crawford et al, , 2000Gehrels, 2001].…”

Section: Geologic Settingmentioning

confidence: 99%

“…Country rocks adjacent to the north end of the body are uniformly kyanite and staurolite bearing, recording depths of $25 km during metamorphism related to emplacement [Crawford et al, 1987[Crawford et al, , 2000. The presence of primary epidote in the pluton suggests that crystallization occurred at $25 km depth [Crawford and Hollister, 1982;Zen and Hammerstrom, 1984].…”

Section: Geologic Settingmentioning

confidence: 99%

“…Geologic map of Prince Rupert region. Distribution of geologic units is from Hutchison [1982], while geologic structures are adapted from Crawford and Hollister [1982] and Crawford et al [1987Crawford et al [ , 2000.…”

Section: Hornblende Geobarometrymentioning

confidence: 99%

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Paleomagnetism and geochronology of the Ecstall pluton in the Coast Mountains of British Columbia: Evidence for local deformation rather than large‐scale transport

et al. 2002

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[1] Samples for geochronologic, geobarometric, and paleomagnetic analyses were collected across the northern portion of the Ecstall pluton southeast of Prince Rupert, British Columbia. Al-inhornblende geobarometry indicates pressures from 740 ± 10 to 840 ± 30 MPa corresponding to crystallization depths of $25 to $30 km. U/Pb analyses of zircons from western, central, and eastern localities within the pluton yield crystallization ages of 91.5 ± 1.0 Ma, 90.8 ± 1.0 Ma, and 90.5 ± 1.0 Ma, respectively. Rock magnetic experiments, reflected light microscopy, and thermal demagnetization behavior suggest that natural remanent magnetism is carried by low-Ti titanohematite. Unblocking temperatures of the characteristic remanent magnetization (ChRM) are dominantly in the 560°C to 630°C range, with age of magnetization approximated by the 40 Ar/ 39 Ar hornblende ages of 84.2 ± 0.10 Ma on the western margin and 76.4 ± 0.6 Ma in the center of the pluton. Site-mean ChRM directions were isolated for paleomagnetic samples from 23 sites and are distributed along a small circle with subhorizontal axis at $340°azimuth. ChRM directions from the central portion of the pluton are concordant with the expected Cretaceous magnetic field direction, while ChRM directions from the western margin are discordant by >70°. Folding of the Ecstall pluton, either during Late Cretaceous west directed thrust transport above the convex upward Prince Rupert Shear Zone or during younger deformation of the pluton and underlying shear zone, can account for the paleomagnetic data and is consistent with the geochronologic, geobarometric, and structural geologic observations.

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Section: Geologic Settingmentioning

confidence: 99%

Section: Geologic Settingmentioning

confidence: 99%

Section: Geologic Settingmentioning

confidence: 99%

Section: Hornblende Geobarometrymentioning

confidence: 99%

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Paleomagnetism and geochronology of the Ecstall pluton in the Coast Mountains of British Columbia: Evidence for local deformation rather than large‐scale transport

et al. 2002

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“…A west-vergent fold-thrust belt, that developed around 100 Ma (Rubin et al 1990;Haeussler 1992), places highgrade rocks of the eastern belt over lower grade rocks of the Gravina-Dezadeash-Nutzotin belt to form a thrust stack that is of higher metamorphic grade upwards (Lynch 1992(Lynch , 1995Journeay and Friedman 1993;Crawford et al 2000;McClelland and Mattinson 2000). Although the deformation is about the same age, the polarity is the reverse of the more southerly batholiths.…”

Section: Comparison With Other Cordilleran Batholithsmentioning

confidence: 99%

Arc and Slab-Failure Magmatism in Cordilleran Batholiths II – The Cretaceous Peninsular Ranges Batholith of Southern and Baja California

Hildebrand

Whalen

2014

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Ever since the late 1960s when Warren Hamilton proposed that the great Cordilleran batholiths of the western Americas are the roots of volcanic arcs like the Andes and were generated by longstanding eastward subduction, most geologists have followed suit, despite the evergrowing recognition that many Cordilleran batholiths are complex, composite bodies that developed with intervals of intense shortening and exhumation between and during periods of magmatism. The Peninsular Ranges batholith of Southern and Baja California provides a superb place to unravel the complexities because there is a lot of data and because it is longitudinally composed of two parts: an older western portion of weakly to moderately deformed, low-grade volcanic and epizonal plutonic rocks ranging in age from ~128–100 Ma; and a more easterly sector of deformed amphibolite grade rocks cut by compositionally zoned, mesozonal plutonic complexes of the La Posta suite, emplaced from 99–86 Ma. While plutons of the La Posta suite are generally considered to be the product of continued eastward subduction, they are enigmatic, because they and their wall rocks were rapidly exhumed from as deep as 23 km and eroded during, and just after, their emplacement, unlike plutons in magmatic arcs, which are generally emplaced in zones of subsidence. Here we resolve the enigma with a model where westward-dipping subduction led to arc magmatism of the western sector, the Santiago Peak–Alisitos composite arc, during the period ~128–100 Ma. Arc magmatism shut down when the arc collided with a west-facing Early Cretaceous passive margin at about 100 Ma. During the collision the buoyancy contrast between the continental crust of the eastern block and its attached oceanic lithosphere led to failure of the subducting slab. The break-off allowed subjacent asthenosphere to upwell, adiabatically melt, and rise into the upper plate to create the large zoned tonalite–granodiorite–granite complexes of the La Posta suite. While compositionally similar to arc plutons in many respects, the examples from the Southern California and Baja segments of the batholith have geochemistry that indicates they were derived from partial melting of asthenosphere at deeper levels in the mantle than typical arc magmas, and within the garnet stability field. This is consistent with asthenosphere upwelling through the torn lower-plate slab. We identify kindred rocks with similar geological relations in other Cordilleran batholiths of the Americas, such as the Sierra Nevada, which lead us to suggest that slab failure magmatism is common, both spatially and temporally.SOMMAIREDepuis la fin des années 1960, Warren Hamilton a proposé que les grands batholites de la Cordillère de l'ouest des Amériques sont les racines d’arcs volcaniques andéens issus de la subduction vers l'est de longue durée, et depuis la plupart des géologues ont emboîté le pas, bien qu’un nombre croissant d’indications montrent que de nombreux batholites de la Cordillère sont des entités composites complexes qui se sont développés lors d’intervalles intenses de contraction et d’exhumation, durant et entre les périodes de magmatisme. Le batholite Peninsular Ranges du Sud de la Californie et de Baja California est un excellent endroit permettant de démêler les choses parce qu'il y a beaucoup de données et parce qu'il est composé longitudinalement de deux parties: une partie occidentale plus ancienne, faiblement à modérément déformée, de roches volcaniques de faible métamorphisme et de roches plutoniques épizonales âgées d’environ 128 Ma à 100 Ma; et, d’un segment plus à l'est de roches amphiboliques déformées recoupées par des roches de composition zonée des complexes mésozonaux plutoniques de la suite de la Posta, mises en place entre 99 Ma et 86 Ma. Bien que les plutons de la suite La Posta sont généralement considérés comme le produit d’une subduction soutenue vers l’est, ils posent problème, parce qu'avec leurs roches encaissantes, ils ont été rapidement exhumés de profondeurs aussi grandes que 23 km, et érodées durant et juste après leur mise en place, contrairement aux plutons des arcs magmatiques, qui sont généralement mis en place dans les zones de subsidence. Dans le présent article, nous proposons une solution à ce problème, avec un modèle de subduction vers l'ouest qui conduit à un magmatisme d'arc du secteur ouest, l'arc composite de Santiago Peak-Alisitos, durant la période d’environ 128 Ma à 100 Ma. Le magmatisme d’arc s’est arrêté lorsque l'arc est entré en collision avec une marge passive à pendage ouest du début du Crétacé, il y a environ 100 Ma. Lors de la collision, le contraste de flottabilité entre la croûte continentale du bloc de est et la lithosphère océanique qui y est rattachée a conduit à l'avortement de la plaque plongeante. La cassure a entrainé la remontée de l’asthénosphère sous-jacente, sa fusion adiabatique, et sa remontée dans la plaque supérieure pour former les grands complexes zonés de tonalite-granodiorite-granite de La Posta. Bien que de composition similaire aux plutons d'arc à bien des égards, les exemples des segments de batholites de Californie du Sud et de Baja ont une géochimie qui indique qu'ils proviennent de la fusion partielle de l’asthénosphère à des niveaux plus profonds dans le manteau que les magmas d'arc typiques, à l’intérieur du domaine de stabilité du grenat. Ce qui correspond à une remontée d’asthénosphère à travers une dalle de plaque inférieure cassée. Nous connaissons des roches semblables avec les relations géologiques similaires dans d'autres batholites de la Cordillère des Amériques, tel celles de la Sierra Nevada, ce qui nous amène à penser que le magmatisme de cassure de plaque est commun, tant spatialement et temporellement.

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Comment on “U‐Pb and Hf Isotope Analysis of Detrital Zircons From Mesozoic Strata of the Gravina Belt, Southeast Alaska” by Yokelson Et Al. (2015)

Lowey

2017

Tectonics

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Yokelson et al. (2015) present U‐Pb and Hf isotope analyses of detrital zircons from the Gravina belt showing that the western facies was derived from the west and the eastern facies was derived from the east and concluded that this is evidence that a west dipping subduction zone did not exist along the inboard margin of the Alexander‐Wrangellia terrane during Late Jurassic‐Early Cretaceous time as proposed by Sigloch and Mihalynuk (2013). However, the tectonic affinity of the eastern Gravina belt is open to debate, and Yokelson et al.'s (2015) claim that the Sigloch and Mihalynuk (2013) model of west dipping subduction was implausible is based on an incorrect assumption.

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

Cited by 16 publications

References 41 publications

Paleomagnetism and geochronology of the Ecstall pluton in the Coast Mountains of British Columbia: Evidence for local deformation rather than large‐scale transport

Paleomagnetism and geochronology of the Ecstall pluton in the Coast Mountains of British Columbia: Evidence for local deformation rather than large‐scale transport

Arc and Slab-Failure Magmatism in Cordilleran Batholiths II – The Cretaceous Peninsular Ranges Batholith of Southern and Baja California

Comment on “U‐Pb and Hf Isotope Analysis of Detrital Zircons From Mesozoic Strata of the Gravina Belt, Southeast Alaska” by Yokelson Et Al. (2015)

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