Wrangellia—A displaced terrane in northwestern North America

Abstract

A large terrane extending along the Pacific margin of North America, from Vancouver Island, British Columbia, to south-central Alaska, is characterized throughout by similar sequences of Triassic rocks. These rocks, including a thick pile of tholeiitic flows and pillow lava (Nikolai Greenstone and Karmutsen Formation) capped with inner-platform carbonates (Chitistone Limestone, Whitestripe Marble, Kunga Formation, and Quatsino Limestone), overlie an upper Paleozoic andesitic arc sequence and Permian argillite and limestone. This coherent terrane, herein named Wrangellia, is juxtaposed against unlike sequences of Triassic and older rocks throughout its extent and is interpreted to be allochthonous. Paleomagnetic data obtained from the Nikolai Greenstone and published in a companion article by Hillhouse indicate that Middle and (or) Upper Triassic rocks in southern Alaska formed in low paleolatitudes, probably within 15° of the paleo-equator.A possible southeastern extension of Wrangellia occurs in the Hells Canyon region of eastern Oregon and western Idaho. This area contains the typical Triassic sequence of Wrangellia and has been interpreted by other geologists as allochthonous. Paleomagnetic data are lacking, however, to document its original latitude.

Oxygen 18/oxygen 16 and D/H studies of plutonic granitic and metamorphic rocks across the Cordilleran Batholiths of southern British Columbia

“…A recent, widely discussed tectonic model for western North America is the "accreted terrane" concept [e.g., Jones et al, 1977;Saleeby, 1983- The paleomagnetic evidence for northward migration exists not only for sedimentary and volcanic sequences but also for the various batholiths. One of the problems with these models is the fact that the ages of some of the studied plutonic terranes are not well known; thus, in some cases it is not known if the paleomagnetic evidence suggests a fit to the North American plate or not [Monger and Irving, 1980].…”

The architecture of oceanic plateaus revealed by the volcanic stratigraphy of the accreted Wrangellia oceanic plateau

“…Wrangellia fl ood basalts are the defi ning unit of Wrangellia, in conjunction with underlying and overlying Triassic sediments with age-diagnostic fossils (Jones et al, 1977). The fl ood basalts are defi ned as the Karmutsen Formation on Vancouver Island and the Queen Charlotte Islands (Haida Gwaii), and the Nikolai Formation in southwest Yukon and south-central Alaska (Fig.…”

“…In this paper Wrangellia (or the Wrangellia terrane) refers to fault-bound sections of the upper crust that contain diagnostic successions of Middle to Late Triassic fl ood basalts and Triassic sedimentary strata that overlie Paleozoic units (as originally defi ned by Jones et al, 1977). The areas of Wrangellia in Alaska and Yukon are referred to as Northern Wrangellia and areas in British Columbia are referred to as Southern Wrangellia.…”

“…). The basement of Wrangellia was originally defi ned as a Pennsylvanian-Permian volcanic arc sequence that may have been deposited on oceanic crust (Jones et al, 1977), and this has been maintained by numerous authors (Smith and MacKevett, 1970;MacKevett, 1978;Coney et al, 1980;Monger et al, 1982;Saleeby, 1983;Beard and Barker, 1989). However, whereas Pennsylvanian-Permian volcanic arcs are preserved in Alaska (Smith and MacKevett, 1970;MacKevett, 1978;Beard and Barker, 1989), older Paleozoic rocks make up much of Vancouver Island (Muller, 1977;Brandon et al, 1986), and there is no signifi cant arc volcanism in the Pennsylvanian-Permian of Vancouver Island ( Fig.…”

Plate-tectonic map of the Circum-Pacific region, Arctic sheet

“…Another plate-tectonic concept, useful in prospecting both for mineral deposits and for petroleum, is the concept of accreted terranes (Jones, Silberling, and Hillhouse, 1977). Accreted terranes are oceanic plateaus, old island arcs, and small detached pieces of continents that move with the seafloor across ocean basins and accumulate at subduction zones as a geologic collage of mixed fragments.…”