Wrangellia Terrane

The Wrangellia Terrane is a geologic concept encompassing a large arc of terrain extending from the south-central part of the U.S state of Alaska through southwestern Yukon and along the Coast of British Columbia in Canada. Although not generally accepted, some workers contend that Wrangellia extends southward to Oregon.

The term Wrangellia is confusingly applied to all of: the Wrangell(ia) Terrane alone; a composite terrane (CT) consisting of the Wrangell Terrane, Peninsular Terrane, and other rock units that were not originally part of the North American craton; and a composite terrane which also includes the Alexander Terrane. Earlier workers sometimes used the term, "Talkeetna Superterrane," to describe Wrangellia.

Rocks of Wrangellia (the individual terrane, not the CT) were originally created in the Pennsylvanian to the Jurassic somewhere, but probably near the equator, in the Panthalassic Ocean off of the west coast of the North American craton as island arcs, oceanic plateaus, and rock assemblages of the associated tectonic settings. Although composed of many different rocks types, of various composition, age, and tectonic affinity, it is the late Triassic flood basalts that are the defining unit of Wrangellia. These basalts, extruded onto land over 5-million years about 230 million years ago, on top of an extinct Pennsylvanian and Permian island arc, constitute a large igneous province, currently exposed in a 2,500 km (1,553 mi) long belt.

Wrangellia collided and amalgamated with the Alexander Terrane by Pennsylvanian time. By the end of the Triassic Period, the Peninsular Terrane had also joined the Wrangellia CT. A subduction zone existed on the west side of Wrangellia. Seafloor rocks too light to be subducted were instead compressed againgst the western edge of Wrangellia; these rocks are now known as the Chugach Terrane. A complex fault system, known as the Border Ranges Fault, is the modern expression of the suture zone between Wrangellia and Chugach Terranes. Over time, plate tectonics moved this amalagamation of crust generally northeastward into contact with the North American continental margin. The Wrangellia CT collided with and docked to North America by Cretaceous time. Strike-slip displacement, with Wrangellia travelling northward, continued after docking, although the amount of post-accretion displacement is controversial.

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