Lithospheric processes and products in the southern Canadian Cordillera: a Lithoprobe perspective

1995 ◽  
Vol 32 (10) ◽  
pp. 1803-1824 ◽  
Author(s):  
Frederick A. Cook
Keyword(s):  
North America ◽  
North American ◽  
Time Interval ◽  
Canadian Cordillera ◽  
Plate Convergence ◽  
The North ◽  
Early Tertiary ◽  
Fracture Systems ◽  
North American Craton ◽  
Oceanic Plates

Analyses of Lithoprobe and other data from southwestern Canada provide new insights on how this portion of the Cordillera formed during plate convergence along the western margin of North America. Crustal rocks are detached from their mantle lithosphere, which must have been consumed during subduction. Detachment occurred at or near the base of the crust beneath the Intermontane and (or) Omineca belts, probably along the tips of tectonic wedges while the rocks were still outboard of the relatively cool, mechanically rigid, North American craton. During the Late Cretaceous and early Tertiary, rotation of detached rocks caught between the North American craton and the oceanic plates accounts for some apparently conflicting results between paleomagnetic data that indicate large northward translation of rocks in the western Cordillera, and regional geological features that appear to preclude comparable amounts of translation of rocks in the eastern Cordillera during the same time interval. Transpression associated with rotation in the Foreland and Omineca belts ceased by the early Tertiary because detached allochthonous rocks of the crust became mechanically attached to, and thus physically part of, North America. Continued plate convergence led to regional transtensional shearing and associated crustal extension in the southern Canadian Cordillera, and perhaps as far inboard as northern Montana, where coeval magmatism was probably associated with new, or reactivation of ancient, lithosphere-penetrating fracture systems.

Kilometre-scale folding in the Teslin zone, northern Canadian Cordillera, and its tectonic implications for the accretion of the Yukon-Tanana terrane to North America

1999 ◽  
Vol 36 (3) ◽  
pp. 479-494 ◽  
Author(s):  
Martin de Keijzer ◽  
Paul F Williams ◽  
Richard L Brown
Keyword(s):  
North America ◽  
Shear Zone ◽  
North American ◽  
Root Zone ◽  
Fault System ◽  
Canadian Cordillera ◽  
The West ◽  
The North ◽  
South Central ◽  
North American Craton

The Teslin zone in south-central Yukon has previously been described as a discrete zone with a steep foliation unique to the zone. It includes the Anvil assemblage and the narrowest portion of the Yukon-Tanana terrane (the Nisutlin assemblage), and is defined by post-accretionary faults: the Big Salmon fault to the west and the d'Abbadie fault system to the east. The zone was interpreted as a lithospheric suture or a crustal-scale transpression zone, and as the root zone of klippen lying on the North American craton to the east. We demonstrate that deformation and metamorphism are the same inside and outside the zone. The steep transposition foliation in the zone, in contrast to adjacent rocks to the east, coincides with the steep limb of a regional F3 structure. This fold has a shallow limb in the easternmost part of the zone and immediately east of the zone. Thus we reject earlier interpretations. If a suture exists between the obducted Anvil and Yukon-Tanana Nisutlin assemblages and North America, it is a shear zone that occurs at the base of the obducted rocks, which has been folded by the F3 fold. However, evidence that this thrust boundary is a lithospheric suture is lacking. A consequence of our interpretation is that North American rocks pass under the eastern Teslin zone and outcrop to the west of the Nisutlin and Anvil assemblages. This geometry precludes the possibility of the Teslin zone being the root zone of the klippen.

Development of late Paleozoic volcanic arcs in the Canadian Cordillera: an example from the Klinkit Group, northern British Columbia and southern Yukon

2003 ◽  
Vol 40 (7) ◽  
pp. 907-924 ◽  
Author(s):  
Renée-Luce Simard ◽  
Jaroslav Dostal ◽  
Charlie F Roots
Keyword(s):  
British Columbia ◽  
North America ◽  
Volcanic Rocks ◽  
Late Paleozoic ◽  
Canadian Cordillera ◽  
Alkali Basalts ◽  
The North ◽  
Pacific Margin ◽  
North American Craton ◽  
Arc Setting

The late Paleozoic volcanic rocks of the northern Canadian Cordillera lying between Ancestral North America to the east and the accreted terranes of the Omineca belt to the west record early arc and rift magmatism along the paleo-Pacific margin of the North American craton. The Mississippian to Permian volcano-sedimentary Klinkit Group extends discontinuously over 250 km in northern British Columbia and southern Yukon. The two stratotype areas are as follows: (1) in the Englishman Range, southern Yukon, the English Creek Limestone is conformably overlain by the volcano-sedimentary Mount McCleary Formation (Lower Clastic Member, Alkali-Basalt Member and Volcaniclastic Member), and (2) in the Stikine Ranges, northern British Columbia, the Screw Creek Limestone is conformably overlain by the volcano-sedimentary Butsih Formation (Volcaniclastic Member and Upper Clastic Member). The calc-alkali nature of the basaltic volcaniclastic members of the Klinkit Group indicates a volcanic-arc setting ((La/Yb)N = 2.77–4.73), with little involvement of the crust in their genesis (εNd = +6.7 to +7.4). Alkali basalts in the Mount McCleary Formation ((La/Yb)N = 12.5–17.8) suggest periodic intra-arc rifting events. Broadly coeval and compositionally similar volcano-sedimentary assemblages occur in the basement of the Mesozoic Quesnel arc, north-central British Columbia, and in the pericratonic Yukon–Tanana composite terrane, central Yukon, suggesting that they all represent pieces of a single long-lived, late Paleozoic arc system that was dismembered prior to its accretion onto Ancestral North America. Therefore, Yukon–Tanana terrane is possibly the equivalent to the basement of Quesnel terrane, and the northern Quesnel terrane has a pericratonic affinity.

Upper Triassic Invertebrates from the Antimonio Formation, Sonora, Mexico

1994 ◽  
Vol 68 (S36) ◽  
pp. 1-33 ◽  
Author(s):  
George D. Stanley ◽  
Carlos González-León ◽  
Michael R. Sandy ◽  
Baba Senowbari-Daryan ◽  
Peter Doyle ◽  
...  
Keyword(s):  
North America ◽  
North American ◽  
Weak Link ◽  
Upper Triassic ◽  
Marine Fauna ◽  
Western Tethys ◽  
The North ◽  
Tethys Realm ◽  
First Occurrence ◽  
North American Craton

A diverse Upper Triassic tropical marine fauna from northwestern Sonora, Mexico, includes 31 taxa of tropical invertebrates including scleractinian corals, spongiomorphs, disjectoporoids, “hydrozoans,” thalamid and nonthalamid sponges, spiriferid and terebratulid brachiopods, gastropods, bivalves, coleoids, and anomuran microcoprolites. They occur within the late Karnian to Norian part of the Antimonio Formation (Antimonio terrane), which is juxtaposed against a fragmented portion of the North American craton. Most of the fauna is also known from the Tethys region. Sixteen Sonoran taxa co-occur in the western Tethys and five have never been known outside this region. Four additional taxa (one identified only at genus level) are geographically widespread. Some taxa occur in displaced terranes of North America, especially in west-central Nevada (Luning Formation). A weak link exists with the California Eastern Klamath terrane but stronger ties exist with Peru. Among Sonoran sponges,Nevadathalamia polystomawas previously recognized only from the Luning Formation, western Nevada. SpongesCinnabaria expansa, Nevadathalamia cylindrica, and a coral,Astraeomorpha sonorensisn. sp., are also known from Nevada. The coralsDistichomeandra austriaca, Chondrocoenia waltheri, Pamiroseris rectilamellosa, andAlpinophyllia flexuosaco-occur in central Europe. Two new taxa, a spongiomorph hydrozoan,Stromatoporidium lamellatumn. sp., and a disjectoporoid,Pamiropora sonorensisn. sp., have distinct affinities with the Tethys. The geographically widespread North American brachiopod,Spondylospira lewesensis, andPseudorhaetina antimoniensisn. gen. and sp. are among the Sonoran fauna. The Sonoran coleoid (aulacocerid)Dictyoconites(Dictyoconites) cf.D. reticulatumoccurs in the Tethys realm andCalliconitescf.C. drakeiis comparable with a species from the Eastern Klamath terrane.Calliconites millerin. sp. is the first occurrence of the genus outside Sicily. The bivalvesMyophorigonia jaworskii, M. salasi, andPalaeocardita peruvianaare known from Sonora and Peru. Eight gastropod taxa includeGuidoniacf.G. intermediaandG.cf.G. parvula, both previously known from Peru, andEucycloscala subbisertusfrom the western Tethys. The gastropods are unlike those already known from other North American terranes.

Nd–Sr isotopic constraints on the interactions of the Intermontane Superterrane with the western edge of North America in the southern Canadian Cordillera

1995 ◽  
Vol 32 (10) ◽  
pp. 1740-1758 ◽  
Author(s):  
Dipak K. Ghosh
Keyword(s):  
North American ◽  
Late Jurassic ◽  
Crustal Contamination ◽  
Late Triassic ◽  
Western Boundary ◽  
Canadian Cordillera ◽  
Isotopic Compositions ◽  
The North ◽  
Tectonic History ◽  
Early Tertiary

Sr and Nd isotopic compositions of the late Paleozoic metavolcanics and Late Triassic to early Tertiary granitoids from four magmatic episodes in the southern Canadian Cordillera from the Kootenay Arc to the Fraser Fault have been used to (i) identify the sources of these rocks, (ii) constrain the compressive tectonic history from Middle Jurassic to Paleocene, and (iii) constrain the western boundary of the basement in this region. The 215–190 Ma old primitive granitoids (εNd = +3.1 to 8.7; 87Sr/86Sr = 0.7028 − 0.7043) of the Late Triassic and Early Jurassic magmatic episode were emplaced in the Paleozoic oceanic crust of Quesnellia (εNd = +2.9 to +9.3) prior to its obduction over the basement. In contrast, during the younger magmatic episodes (Middle–Late Jurassic, Cretaceous, and early Tertiary), the granitoids from western Quesnellia show primitive isotopic compositions, and those from eastern Quesnellia show eastward-increasing crust-contaminated compositions. The contaminated characters of the Middle–Late Jurassic (180–150 Ma) granitoids from eastern Quesnellia (εNd = +2.8 to −9.1; 87Sr/86Sr = 0.7041 − 0.7083) suggest that by 180 Ma, the eastern part of Quesnellia obducted over the North American cratonic basement by an amount of about 100 km (Eocene extension corrected) measured from westward shifts of the Nd and Sr isopleths. The eastward-increasing crustal-contamination patterns in the Cretaceous (120–80 Ma) and the Paleocene igneous rocks also show westward shifts of these isopleths by 20 and 70 km, respectively. Thus, we observe that a total 190 km of obduction took place, this amount is similar to the amount of shortening measured in the Rocky Mountains Fold and Thrust Belt, and the western boundary of the North American basement presently lies at least 25–75 km east of the Fraser Fault.

scholarly journals Graptolite and conodont faunas in Ordovician Vinini Formation, Roberts Mountains, central Nevada, demonstrate that the Roberts Mountains allochthon is not an exotic terrane

1992 ◽  
Vol 6 ◽  
pp. 97-97
Author(s):  
Stanley C. Finney ◽  
Raymond L. Ethington
Keyword(s):  
North America ◽  
Shallow Water ◽  
North American ◽  
Cold Water ◽  
Turbidity Currents ◽  
Plate Tectonic ◽  
Continental Rise ◽  
The North ◽  
North American Craton ◽  
Back Arc

Two very different plate-tectonic models have been proposed to explain the development and emplacement of the Robert Mountains allochthon (RMA) onto the North America craton during the Late Devonian-Early Mississippian Antler Orogeny. In one model, the RMA represents a far-traveled accretionary prism that migrated eastwards over a west-dipping subduction zone. In the other, the eugeoclinal strata of the RMA were deposited on the continental rise of western North America within a closed back-arc basin. Siliciclastic sediments, especially quartz sandstones, compose much of the RMA, yet knowledge of their provenance is poor even though such knowledge is essential for evaluating the two plate-tectonic models.We have recently obtained large collections of graptolites and conodonts from turbiditic quartz sandstones in the Lower Member of the Vinini Formation in the Roberts Mountains. These sandstones of lower Whiterockian age are correlative with the lower Antelope Valley Limestone that deposited on the western shelf of North America. The diverse graptolite fauna represents the oceanic isograptid fauna. However, it also includes pendent didymograptids and rooted dendroids that were restricted to shallow shelf seas. The dendroids (Cactograptus, Dendrograptus, Desmograptus, and Dictyonema) were benthic organisms, could not have lived in a deep marine setting, and are also common in shallow-water carbonate strata of western Utah. All specimens within the turbiditic quartz sandstones of the Vinini were broken before final deposition and burial, but specimens from Utah are generally complete. The diverse conodont fauna is virtually identical to that found in the lower Antelope Valley Limestone, as well as in coeval strata in western Utah. Although it includes a few deep (cold) water, cosmopolitan species, it is dominated by species that are otherwise known only from shallow water strata deposited on the North American craton.We conclude that turbidity currents transported these exotic graptolites and conodonts down from the shelf and onto the rise along with the quartz sands in which they occur. Thus, the Whiterockian quartz sandstones in the Vinini Formation must have a North American provenance just as the fossils do. This is strong evidence that 1) the RMA is not exotic to North America, 2) the eugeoclinal strata of the RMA were deposited on the western continental rise of North America and on the eastern side of a back-arc basin, and 3) the RMA was thrust onto the western shelf of North America by closure of this back-arc basin.

The occurrence of the hydrozoan genus Cassianastraea from Upper Triassic (Carnian) rocks of Williston Lake, British Columbia, Canada

2011 ◽  
Vol 85 (1) ◽  
pp. 29-31
Author(s):  
George D. Stanley ◽  
John-Paul Zonneveld
Keyword(s):  
British Columbia ◽  
North America ◽  
Coral Reefs ◽  
North American ◽  
Upper Triassic ◽  
Geological Survey ◽  
The North ◽  
Lake Region ◽  
First Occurrence ◽  
North American Craton

Cassianastraea is an enigmatic colonial Triassic cnidarian first described as a coral but subsequently referred to the Hydrozoa. We report here the first occurrence in Canada of fossils we designate as Cassianastraea sp. from the Williston Lake region of British Columbia. The specimens come from older collections of the Geological Survey of Canada, collected in Upper Triassic (Carnian) strata assigned to either the Ludington or Baldonnel Formations. While well known in reef associations of the former Tethys region, Cassianiastraea is relatively rare in North America. The Carnian Baldonnel Formation contains the earliest coral reefs from the North American craton and we suspect that Cassianastraea sp. also came from this reef association.

scholarly journals Geology, Mantle Tomography, and Inclination Corrected Paleogeographic Trajectories Support Westward Subduction During Cretaceous Orogenesis in the North American Cordillera

2014 ◽  
Vol 41 (2) ◽  
pp. 207 ◽  
Author(s):  
Robert S. Hildebrand
Keyword(s):  
North America ◽  
North American ◽  
Passive Margin ◽  
Canadian Cordillera ◽  
Western North America ◽  
Geological Evidence ◽  
North American Cordillera ◽  
The North ◽  
Independent Verification ◽  
Haute Résolution

Geological evidence, including the presence of two passive margin platforms, juxtaposed and mismatched deformation between North America and more outboard terranes, as well as the lack of rift deposits, suggest that North America was the lower plate during both the Sevier and Laramide events and that subduction dipped westward beneath the Cordilleran Ribbon Continent (Rubia). Terranes within the composite ribbon continent, now present in the Canadian Cordillera, collided with western North America during the 125–105 Ma Sevier event and were transported northward during the ~80–58 Ma Laramide event, which affected the Cordillera from South America to Alaska. New high-resolution mantle tomography beneath North America reveals a huge slab wall that extends vertically for over 1000 km, marks the site of long-lived subduction, and provides independent verification of the westward-dipping subduction model. Other workers analyzed paleogeographic trajectories and concluded that the initial collision took place in Canada at about 160 Ma – a time and place for which there is no deformational thickening on the North American platform – and later farther west where subduction was not likely westward, but eastward. However, by utilizing a meridionally corrected North American paleogeographic trajectory, coupled with the geologically most reasonable location for the initial deformation, the position of western North America with respect to the relict superslab parsimoniously accounts for the timing and extents of both the Sevier and Laramide events. SOMMAIRELes indications géologiques, en particulier la présence de deux marges de plateforme passives, de déformations adjacentes non-conformes entre l’Amérique du Nord et les terranes extérieurs, ainsi que l’absence de gisements de rift, permet de croire que l’Amérique du Nord était la plaque sous-jacente durant les événements de Sevier et de Laramide et que la subduction plongeait vers l’ouest sous le continent rubané de la Cordillères (Rubia).  Les terranes du continent rubané composite, maintenant au sein de la Cordillère canadienne, sont entrés en collision avec l’ouest de l’Amérique du Nord durant l’événement Sevier (125-105 Ma), et ont été transportés vers le nord durant l’événement Laramide (~80–58 Ma), laquelle a affecté la Cordillère, de l’Amérique du Sud à l’Alaska.  Une nouvelle tomographie haute résolution du manteau sous l’Amérique du Nord montre la présence d’un gigantesque mur de plaques vertical qui s’étend sur 1 000 km, marque le site d’une subduction de longue haleine, et offre une validation indépendante du modèle d’une subduction à pendage vers l’ouest.  D’autres chercheurs ont analysé les trajectoires paléogéographiques et conclu que la collision initiale s’est produite au Canada vers 160 Ma – un moment et un endroit sans épaississement par déformation sur la plateforme d’Amérique du Nord – et plus tard plus à l’ouest, là où la subduction n’était vraisemblablement pas vers l’ouest, mais vers l’est.  Cela dit, en considérant une trajectoire paléogéographique de l’Amérique du Nord corrigée longitudinalement, avec la position géologique la plus probable de la déformation initiale, la position de la portion ouest de l’Amérique du Nord par rapport aux restes de la super-plaque explique alors facilement la chronologie et l’étendue des épisodes Sevier et Laramide.

Upper Triassic sponges (Sphinctozoa) from southern Yukon, Stikinia terrane

1987 ◽  
Vol 24 (5) ◽  
pp. 882-902 ◽  
Author(s):  
Baba Senowbari-Daryan ◽  
R. Pamela Reid
Keyword(s):  
Pacific Ocean ◽  
North America ◽  
North American ◽  
Upper Triassic ◽  
The North ◽  
North American Craton ◽  
First Time ◽  
Sponge Reefs

The first Tethyan-type Upper Triassic sponge reefs in North America have recently been discovered in the southern Yukon, in Stikinia terrane. Sphinctozoa from these reefs and inter-reef limestones are represented by 18 species and 12 genera belonging to six families. The genus Yukonella with one species, Y. rigbyi, and the species Polytholosia ramosa and Polycystocoelia norica are described for the first time. Some of the Yukon sponges were previously known only from the Tethyan realm (Colospongia, Dictyocoelia, Polycystocoelia, and Uvanella?); others, from Tethyan and North American localities (Ascosymplegma, Follicatena, Paradenigeria, and Salzburgia?). One (Polytholosia cylindrica) is probably endemic to North America. The mixed affinities of the Yukon sponges may reflect the paleogeographic origin of Stikinia as an island in the ancestral Pacific Ocean, between Tethys and the North American craton.

The occurrence of the brachiopods Nanukidium and Atrypoidea in the Late Silurian of southeastern Alaska, Alexander terrane

1989 ◽  
Vol 63 (4) ◽  
pp. 530-533 ◽  
Author(s):  
Norman M. Savage
Keyword(s):  
North America ◽  
North American ◽  
Canadian Arctic ◽  
The North ◽  
Middle Paleozoic ◽  
History Of ◽  
North American Craton ◽  
Alexander Terrane

Previously described faunas of Early Silurian through Late Pennsylvanian age from the Alexander terrane have been endemic, or have variously suggested North American or Asiatic affinities, leaving the paleogeographic history of the terrane uncertain although indicating a location closer to North America than to Asia (Armstrong, 1970; Douglass, 1971; Savage, 1981, 1985, 1989; Savage et al., 1978; Savage and Barkeley, 1985; Soja, 1988; Vaskey, 1982). The occurrence reported here of the Canadian Arctic brachiopods Nanukidium cf. N. cunninghamensis and Atrypoidea scheii in the Alexander terrane during the Late Silurian could be additional evidence supporting the view that the Alexander terrane was not far removed from the North American craton during middle Paleozoic time.

Tectonic interpretation of west-verging folds in the Selkirk Allochthon of the southern Canadian Cordillera

1988 ◽  
Vol 25 (2) ◽  
pp. 292-300 ◽  
Author(s):  
Richard L. Brown ◽  
Larry S. Lane
Keyword(s):  
North American ◽  
Late Jurassic ◽  
Shear Zones ◽  
Canadian Cordillera ◽  
Fundamental Change ◽  
The West ◽  
The North ◽  
North American Craton ◽  
Tectonic Slice ◽  
Tectonic Interpretation

The Selkirk Allochthon, a composite tectonic slice composed of North American paleocontinental-margin deposits and more distal, possibly marginal-basin "suspect terrane," was displaced eastward toward the craton in the Late Jurassic and Late Cretaceous.The Carnes Nappe, a major west-verging recumbent anticline within the Selkirk Allochthon, is considered the southern continuation of Scrip Nappe, which in the Monashee Mountains has an inverted limb length of 50 km. The west-verging nappe and associated structures are interpreted as having originated in the Early to Middle Jurassic during accretion of western allochthonous terranes and prior to eastward displacement of the Selkirk Allochthon.The reversal from westward vergence away from the North American craton to eastward vergence is considered as marking a fundamental change in the evolution of the orogenic belt and may reflect a transition from underthrusting of western allochthonous terranes on blind-shear zones to east-directed breakthrough thrusts.

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