Geology of the Pacific Northwest debris. Rising above this volcanic platform are a few strikingly large volcanoes that dominate the landscape. The Cascade volcanoes define the Pacific Northwest section of the Ring of Fire, an array of volcanoes that rim the Pacific Ocean. The Ring of Fire is also known for its frequent earthquakes. The volcanoes and earthquakes arise from a common source: subduction. Beneath the Cascade Volcanic Arc, a dense oceanic plate plunges beneath the North American Plate; a process known as subduction. As the oceanic slab sinks deep into the Earth's interior beneath the continental plate, high temperatures and pressures allow water molecules
Circum-Superior Belt remain undated, indicating the existence of magmatic rocks with the same age as those of the Circum-Superior Belt is probable. It contains two large copper-nickel mining districts; the nickel-bearing Thompson Belt at the northwestern portion of the Superior craton and the Cape Smith Belt at the northern portion of the Circum-Superior Belt. The Circum-Superior Belt was formed 1,884 to 1,864 million years ago when the Superior craton was surrounded by mountain building processes, including the Trans-Hudson, New Quebec and Penokean orogenies. The major Trans-Hudson orogeny had its appearance when the Superior craton collided with the Rae-Hearne craton 1,900 to 1,800