The Insular Islands were an extended chain of

volcanic island Geologically, a high island or volcanic island is an island of volcanic origin. The term can be used to distinguish such islands from low islands, which are formed from sedimentation or the uplifting of coral reefs (which have often formed ...

s forming an arc in what is now the

Pacific Ocean The Pacific Ocean is the largest and deepest of Earth's five oceanic divisions. It extends from the Arctic Ocean in the north to the Southern Ocean (or, depending on definition, to Antarctica) in the south, and is bounded by the contin ...

during the

Paleozoic The Paleozoic (or Palaeozoic) Era is the earliest of three geologic eras of the Phanerozoic Eon. The name ''Paleozoic'' ( ;) was coined by the British geologist Adam Sedgwick in 1838 by combining the Greek words ''palaiós'' (, "old") and ' ...

and

Mesozoic The Mesozoic Era ( ), also called the Age of Reptiles, the Age of Conifers, and colloquially as the Age of the Dinosaurs is the second-to-last era of Earth's geological history, lasting from about , comprising the Triassic, Jurassic and Cretace ...

eras. The islands formed by subduction and melting of the

Farallon Plate The Farallon Plate was an ancient oceanic plate. It formed one of the three main plates of Panthalassa, alongside the Phoenix Plate and Izanagi Plate, which were connected by a triple junction. The Farallon Plate began subducting under the west ...

along a fragment (or microplate) upon which they rose called the Insular Plate. They were bounded by the Panthalassic Ocean to the west and the Bridge River Ocean 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 The Cretaceous ( ) is a geological period that lasted from about 145 to 66 million years ago (Mya). It is the third and final period of the Mesozoic Era, as well as the longest. At around 79 million years, it is the longest geological period of ...

they finally collided with and fused onto the

North American Plate The North American Plate is a tectonic plate covering most of North America, Cuba, the Bahamas, extreme northeastern Asia, and parts of Iceland and the Azores. With an area of , it is the Earth's second largest tectonic plate, behind the Pacif ...

. Like the earlier

Intermontane Islands 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 long and rode atop a microplate known as the Intermontane Plate ...

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 and closed the Bridge River Ocean. The subduction zone moved westward to the

Farallon Trench The Farallon Trench was a subduction related tectonic formation located off the coast of the western California continental margin during the late to mid Cenozoic era, around 50 miles southeast of modern-day Monterey Bay. The time duration of subd ...

, causing new volcanism which formed the Coast Range Arc. Rocks of the Insular Islands now comprise wide sections of the westernmost coast of the North American plate. This includes both the

Insular Mountains The Insular Mountains are a range of mountains in the Pacific Coast Ranges on the Coast of British Columbia, Canada, comprising the Vancouver Island Ranges and Queen Charlotte Mountains. The Insular Mountains are rugged, particularly on Vancou ...

of the

Alaskan Panhandle Southeast Alaska, colloquially referred to as the Alaska(n) Panhandle, is the southeastern portion of the U.S. state of Alaska, bordered to the east and north by the northern half of the Canadian province of British Columbia (and a small part ...

Haida Gwaii Haida Gwaii (; hai, X̱aaydag̱a Gwaay.yaay / , literally "Islands of the Haida people") is an archipelago located between off the northern Pacific coast of Canada. The islands are separated from the mainland to the east by the shallow Heca ...

, and

Vancouver Island Vancouver Island is an island in the northeastern Pacific Ocean and part of the Canadian province of British Columbia. The island is in length, in width at its widest point, and in total area, while are of land. The island is the largest by ...

, and sunken areas of the greater Insular Belt which takes into consideration rock formed on the floor of the Bridge River Ocean. This extends to the northern

North Cascades The North Cascades are a section of the Cascade Range of western North America. They span the border between the Canadian province of British Columbia and the U.S. state of Washington and are officially named in the U.S. and Canada as the Casca ...

range in

Washington State Washington (), officially the State of Washington, is a state in the Pacific Northwest region of the Western United States. Named for George Washington—the first U.S. president—the state was formed from the western part of the Washington ...

, perhaps as far as the

Wallowa Mountains The Wallowa Mountains () are a mountain range located in the Columbia Plateau of northeastern Oregon in the United States. The range runs approximately northwest to southeast in southwestern Wallowa County and eastern Union County between the ...

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 10 kilometer wide Ross Lake fault zone (RLFZ) is part of a 500 kilometer long zone of high-angle faults in the North American Cordillera of Washington and Canada. The RLFZ consists of two major sets of faults. The eastern set of the Hozameen ...

."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