The Insular Islands were an extended chain of volcanic islands forming an arc in what is now the Pacific Ocean during the Paleozoic and Mesozoic eras. The islands formed by subduction and melting of the Farallon Plate along a fragment (or microplate) upon which they rose called the

Insular Plate The Insular Plate was an ancient oceanic plate that began subducting under the west-coast of North America around the early Cretaceous period. The Insular Plate had a chain of active volcanic islands that were called the Insular Islands. These v ...

. They were bounded by the

Panthalassic Ocean Panthalassa, also known as the Panthalassic Ocean or Panthalassan Ocean (from Greek "all" and "sea"), was the superocean that surrounded the supercontinent Pangaea, the latest in a series of supercontinents in the history of Earth. During the ...

to the west and the

Bridge River Ocean The Bridge River Ocean was an ancient ocean that existed between North America and the Insular Islands during the Mesozoic era. Similar to the earlier Slide Mountain Ocean, the Bridge River Ocean had a subduction zone on the ocean floor called the ...

to the east. They probably formed as a composite of several volcanic chains near the equator, offshore of continental landmasses, by the Carboniferous Period around 300-325 million years ago. The chain continually moved northward during the Mesozoic. About 115 million years ago in the mid- Cretaceous they finally collided with and fused onto the North American Plate. Like the earlier Intermontane Islands which underwent a similar continental accretion 60 million years before, the large mass of the islands prevented them from being pushed under the North American Plate. This violent collision halted subduction which fed volcanic activity in the

Omineca Arc The Omineca Arc or Omineca Belt was a Jurassic through Cretaceous volcanic arc terrane in western North America, extending from Alaska through Yukon and British Columbia to Washington. The Omineca is bounded by the Foreland Belt to the east and t ...

and closed the Bridge River Ocean. The

subduction zone Subduction is a geological process in which the oceanic lithosphere is recycled into the Earth's mantle at convergent boundaries. Where the oceanic lithosphere of a tectonic plate converges with the less dense lithosphere of a second plate, the ...

moved westward to the Farallon Trench, causing new volcanism which formed the

Coast Range Arc The Coast Range Arc was a large volcanic arc system, extending from northern Washington through British Columbia and the Alaska Panhandle to southwestern Yukon. The Coast Range Arc lies along the western margin of the North American Plate in the P ...

. Rocks of the Insular Islands now comprise wide sections of the westernmost coast of the North American plate. This includes both the Insular Mountains of the Alaskan Panhandle, Haida Gwaii, and Vancouver Island, and sunken areas of the greater

Insular Belt The Insular Belt is a physical geography, physiogeological region on the north western North American coast. It consists of three major island groups and many smaller islands and stretches from southern British Columbia into Alaska and the Yukon. I ...

which takes into consideration rock formed on the floor of the Bridge River Ocean. This extends to the northern North Cascades range in Washington State, perhaps as far as the Wallowa Mountains in northeastern Oregon which may be a displaced fragment from the Insular Belt. The "suture" at the former continental margin is now a major northwest-trending fault through the North Cascades, the 10 kilometers wide, 500 kilometer long Ross Lake Fault."The Coast Range Episode".
The Burke Museum of Natural History and Culture. Retrieved 1 January 2010.

References

Former islands Geology of North America Volcanic arc islands Cretaceous volcanism {{Palaeo-geo-stub

See also

References