Intermontane Islands

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The Intermontane Islands were a giant chain of active volcanic islands somewhere in the Pacific Ocean during the Triassic time beginning around 245 million years ago. They were 600 to 800 miles (1,300 km) long and rode atop a microplate known as the Intermontane Plate. Over early Jurassic time the Intermontane Islands and the Pacific Northwest drew closer together as the continent moved west and the Intermontane Plate subducted. About 180 million years ago in the Mid-Jurassic time the last of the Intermontane Plate subducted and the Intermontane Islands collided with the Pacific Northwest, forming parts of British Columbia, Canada. The Intermontane Islands were too big to sink beneath the continent, and welded onto the continent, forming the Intermontane Belt. Geologists call the ocean that existed between the Intermontane Islands and North America the Slide Mountain Ocean.

Pacific Ocean Ocean between Asia and Australia in the west, the Americas in the east and Antarctica or the Southern Ocean in the south.

The Pacific Ocean is the largest and deepest of Earth's oceanic divisions. It extends from the Arctic Ocean in the north to the Southern Ocean in the south and is bounded by Asia and Australia in the west and the Americas in the east.

The Triassic is a geologic period and system which spans 50.6 million years from the end of the Permian Period 251.9 million years ago (Mya), to the beginning of the Jurassic Period 201.3 Mya. The Triassic is the first and shortest period of the Mesozoic Era. Both the start and end of the period are marked by major extinction events.

The Intermontane Plate was an ancient oceanic tectonic plate that lay on the west coast of North America about 195 million years ago. The Intermontane Plate was surrounded by a chain of volcanic islands called the Intermontane Islands, which had been accumulating as a volcanic chain in the Pacific Ocean since the Triassic period, beginning around 245 million years ago. The volcanism records yet another subduction zone. Beneath the far edge of the Intermontane microplate, another plate called the Insular Plate was sinking. This arrangement with two parallel subduction zones is unusual. The modern Philippine Islands are located on the Philippine Mobile Belt, one of the few places on Earth where twin subduction zones exist today. Geologists call the ocean between the Intermontane islands and North America the Slide Mountain Ocean. The name comes from the Slide Mountain Terrane, a region made of rocks from the floor of the ancient ocean.

See also

Island arc arc-shaped archipelago

Island arcs are long chains of active volcanoes with intense seismic activity found along convergent tectonic plate boundaries. Most island arcs originate on oceanic crust and have resulted from the descent of the lithosphere into the mantle along the subduction zone. They are the principal way by which continental growth is achieved.

Insular Islands chain of active volcanic islands in the Pacific Ocean during the Cretaceous period on the Insular Plate; 115 million years ago, collided with the North American continent to form the Insular Mountains

The Insular Islands were a giant chain of active volcanic islands somewhere in the Pacific Ocean during the Cretaceous period that rode on top a microplate called the Insular Plate, beginning around 130 million years ago. The Insular Islands were surrounded by two prehistoric oceans, the Panthalassa Ocean to the west and the Bridge River Ocean to the east. About 115 million years ago, these islands collided with the North American continent, fusing onto the North American Plate and closing the Bridge River Ocean during the Mid-Cretaceous time.

Intermontane Belt

The Intermontane Belt is a physiogeological region in the Pacific Northwest of North America, stretching from northern Washington into British Columbia, Yukon, and Alaska. It comprises rolling hills, high plateaus and deeply cut valleys. The rocks in the belt have very little similarities with the North American continent.

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