Petrologic evolution and paleogeography of the Late Cretaceous Nanaimo Basin, Washington and British Columbia: Implications for Cretaceous tectonics

Pacht, Jory A.

doi:10.1130/0016-7606(1984)95<766:peapot>2.0.co;2

Cited by 35 publications

(36 citation statements)

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“…Early interpretations suggested that Wrangellia was the main source of sediment for the Nanaimo basin, with minor input from the North Cascades and CPC [e.g., Muller and Jeletzky , ]. Based on sandstone composition and paleocurrent measurements, Ward and Stanley [] and Pacht [] concluded that the sediments were largely sourced from the CPC, Northern Cascades, and San Juan Islands to the east. Paleocurrent directions in the Nanaimo Group within the study area are dominantly to the southwest and west reinforcing an easterly provenance [ Katnick and Mustard , ; Bain and Hubbard , ].…”

Section: Nanaimo Group Geological Settingmentioning

confidence: 99%

Detrital zircons from the Nanaimo basin, Vancouver Island, British Columbia: An independent test of Late Cretaceous to Cenozoic northward translation

et al. 2017

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The development of the Cordilleran orogen of western North American is disputed despite a century of study. Paleomagnetic observations require large‐scale dextral displacements of crustal fragments along the western margin of North America, from low latitudes to moderate latitudes during the Cretaceous‐Paleogene. A lack of corroborating geological evidence for large‐scale (>1500 km) displacements has prevented the widespread integration of paleomagnetic data into most contemporary tectonic models for the margin. Here we use detrital zircons from the Nanaimo basin, southwestern British Columbia, Canada as an independent test of its Late Cretaceous paleogeographic position. We compare 4310 detrital zircon U/Pb dates from 16 samples to potential source areas in western North America to test hypothesized northern and southern Late Cretaceous paleogeographic positions. Our detrital zircon data suggest that sediment in the Nanaimo basin derives from either a geographically restricted portion of the Belt‐Purcell basin or the Mojave‐Sonoran region of southwestern North America. A paleogeographic position for the basin adjacent to the Mojave‐Sonoran region is preferred as it is consistent with the paleomagnetic results, but further geological, isotopic, or geophysical data are required to rule out a Belt‐Purcell source.

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Section: Nanaimo Group Geological Settingmentioning

confidence: 99%

Detrital zircons from the Nanaimo basin, Vancouver Island, British Columbia: An independent test of Late Cretaceous to Cenozoic northward translation

et al. 2017

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“…Blueschist cobbles correlative to the Easton are found in Nanaimo Group conglomerates [Vance, 1975], indicating exhumation of the Shuksan nappe during the Late Cretaceous. Deposition in the Nanaimo foreland basin ceased at the end of the Cretaceous [Pacht, 1984], which implies that thrusting was largely finished by that time. The Eocene Chuckanut Group is the oldest unit that definitively overlies the SJC nappes, both in the NW Cascades and in the eastern San Juan Islands [Vance, 1975;Johnson, 1984].…”

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confidence: 99%

Contribution of ductile flow to exhumation of low‐temperature, high‐pressure metamorphic rocks: San Juan‐Cascade nappes, NW Washington State

Feehan¹,

Brandon²

1999

J. Geophys. Res.

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“…They also published new fossil ages and isotopic dates, which established a Mesozoic age for many of the rock units in the archipelago. Other recent contributions to the geology of the islands include: the stratig raphy of the Nanaimo Group (Ward, 1978;Johnson, 1978;Ward and Stanley, 1982;Pacht, 1984); the stratigraphy of the Spieden Group and Haro Formation (Johnson, 1978(Johnson, , 1981; and mapping of Lopez Island (Cowan and Miller, 1981), southern San Juan Island (Brandon, 1980), Lummi Island (Carroll, 1980), and Fidalgo Island (Brown, 1977;Gusey, 1978;Brown and oth ers, 1979).…”

Section: Previous Workmentioning

confidence: 99%

The Late Cretaceous San Juan thrust system, San Juan Islands, Washington

Brandon

Cowan²,

Vance³

1988

Geological Society of America Special Papers

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The San Juan Islands expose a thick and regionally extensive sequence of Late Cretaceous thrust faults and nappes, referred to as the San Juan thrust system. This thrust system, which straddles the southeastern edge of the Wrangellia terrane of Van couver Island, contains important information on the accretionary history of Wrangellia and other, related, far-traveled terranes. Nappes of the thrust system contain a diverse group of rocks ranging from early Paleozoic to middle Cretaceous in age. Based on contrasts in stratigraphy, metamorphism, and geochemistry, we identify five terranes within, and peripheral to, the thrust system. These terranes were widely separated from each other, and also from Wrangellia, until the Late Jurassic: (1) the Haro terrane, an Upper Triassic arc-volcanic sequence; (2) the Turtleback terrane, a Paleozoic arc plutonic and volcanic unit; (3) the Deadman Bay terrane, a Permian to Lower Jurassic oceanic-island sequence containing Tethyan-fusulinid timestones; (4) the Garrison ter rane, a Permo-Triassic, high-pressure metamorphic unit; and (5) the Decatur terrane, a Middle to Upper Jurassic ophiolite and superimposed arc-volcanic sequence. Thick Jura-Cretaceous clastic units are linked to these older San Juan terranes and to Wran gellia, either as directly overlapping units or by the presence of clastic material derived from the terranes. The voluminous amount of clastic material in these Jura-Cretaceous units requires a large, subaerially exposed source region. We infer that this source region was a continent-like landmass, presumably part of continental America (North or Central?). Late Cretaceous thrusting juxtaposed these older terranes and disrupted the Jura Cretaceous clastic units. Very low-temperature high-pressure metamorphic assem blages, including lawsonite and aragonite, were developed during this event, and formed as a direct result of thrust-related burial to depths of about 20 km. Stratigraphic evi dence indicates that structural burial, metamorphism, and subsequent uplift back to the surface all occurred during a very short time interval, between 100 and 84 Ma, with average vertical transport rates of about 2 km/m.y. The Upper Cretaceous Nanaimo Group, a syn-orogenic basin to the north of the San Juan system, contains cobbles of metamorphosed rocks from the San Juan nappes, and therefore records the erosional unroofing of the thrust system. We envision the San Juan system to be a short-lived collision-like orogen, rather than a long-lived subduction complex. This conclusion is based primarily on the diver sity of rock units involved and the punctuated nature of the deformation. What remains unclear is the cause of this orogenic deformation. The clastic-rich Jura-Cretaceous units imply that Wrangellia and the older San Juan terranes were adjacent to or part of the American continent by latest Jurassic time. Moreover, there is no evidence for the arrival and collision of an exotic terrane during the Cretaceous. As a result, the San Juan system is considered to be the produc...

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Petrologic evolution and paleogeography of the Late Cretaceous Nanaimo Basin, Washington and British Columbia: Implications for Cretaceous tectonics

Cited by 35 publications

References 0 publications

Detrital zircons from the Nanaimo basin, Vancouver Island, British Columbia: An independent test of Late Cretaceous to Cenozoic northward translation

Detrital zircons from the Nanaimo basin, Vancouver Island, British Columbia: An independent test of Late Cretaceous to Cenozoic northward translation

Contribution of ductile flow to exhumation of low‐temperature, high‐pressure metamorphic rocks: San Juan‐Cascade nappes, NW Washington State

The Late Cretaceous San Juan thrust system, San Juan Islands, Washington

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