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.