Kula Plate

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The Kula Plate was an ancient oceanic plate, which began subducting under Alaska as Pangaea broke apart during the Jurassic period. The Kula Plate subducted under Alaska much like the Pacific Plate does. There was a triple junction of three ridges between the Kula Plate to the north, the Pacific Plate to the west and the Farallon Plate to the east called the Kula Ridge. The Kula Plate was subducted under the North American Plate at a relatively steep angle, so that the Canadian Rockies are primarily comprised of thrusted sedimentary sheets with relatively little contribution of continental uplift, while the American Rockies are characterized by significant continental uplift in response to the shallow subduction of the Farallon Plate. About 55 million years ago, the Kula Plate began an even more northerly motion. Riding on the Kula Plate was the Pacific Rim Terrane consisting of volcanic and sedimentary rocks. It was scraped off and plastered against the continental margin, forming what is today Vancouver Island. By 40 million years ago, the compressional force of the Kula Plate ceased. The existence of the Kula Plate was inferred from the westward bend in the alternating pattern of magnetic anomalies in the Pacific Plate.