Abstract

The Seven Devils terrane of eastern Oregon and western Idaho has been correlated with the Wrangellia terrane, which is best exposed on Vancouver Island, British Columbia, and in the Wrangell Mountains, Alaska. However, geologic histories of these two terranes are different. The Triassic section of the Seven Devils terrane represents a volcanic arc of probable calc-alkalic affinity. It is characterized by abundant volcaniclastic lithologies, a complete suite of flow rocks, and fractionated rare-earth-element distribution patterns. The sequence of similar age in Wrangellia includes thick accumulations of tholeiitic pillow basalts, subaerial basalt flows, tuffs, and breccias. The tectonic environment in which these rocks were extruded is not known, but they are not an island-arc assemblage. Paleomagnetic and faunal evidence suggests that the Seven Devils terrane and Wrangellia could have formed close to one another. This evidence does not override the geologic arguments against correlation of these terranes. Lithologic, geochemical, and stratigraphic data all militate against consanguinity of the Seven Devils arc and Wrangellia.

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