Geology of British Columbia - Architecture and Composition

Architecture and Composition

There are five morpho-geological belts that define the geology of British Columbia from east to west: the Foreland, Omineca, Intermontane, Coast and Insular Belt. Each has a separate geology, including different metamorphic, physiograhpic, metallogenic and tectonic histories.

The Foreland Belt is composed of weakly metamorphosed sedimentary rocks which are 1.4 billion to 33 million years old, and the belt represents a rift sequence followed by a passive margin that was turned into a retro arc fold and thrust belt with synorogenic sedimentation. The region is very rugged except in the northeast of the province where the earth flattens out to a wide plain.

The Omineca Belt is composed of highly metamorphosed, pericratonic (near craton) terranes and fragments of North America that are 2 billion to 180 million years old. Terranes in the belt include the Slide Mountain Terrane, the Yukon-Tanana Terrane and the Cassiar Terrane. This belt goes from low hills to high mountains across its length, with the majority of the region being extremely rugged.

The Intermontane Belt is a flatter, more rounded region composed of three terranes, Stikinia, Quenellia and the Cache Creek Terrane. The belt has a lower metamorphic grade than the Omineca Belt and ranges from 400 million to within 10,000 years old. Volcanic activity has been recorded as occurring in the past 10,000 years, including at Nazko Cone and in the Satah Mountain volcanic field.

The Coast Belt is the single largest outpouring of granite and granodiorite in the phanerozoic, it contains heavily metamorphosed fragments of both the terranes of the Insular Belt and the Intermontane Belt. In the southeast there is a series of small terranes of both oceanic (Bridge River and Chilliwack) and continental affinity (Jack Konat Mountain, Ladner). The hard weathering granite is extensively rugged the throughout the belt.

The Insular Belt is composed of the outboard terrain with no connection to North America before accretion. There are two main terranes—Wrangellia and the Alexander—and few smaller ones such as the Leech River and Crescent terranes. Because the Insular Belt is the most tectonically active of the belts, it has the greatest relief differences from the depths of Queen Charlotte sound to the heights of the Wrangell–St. Elias mountains. The ages are from 600 million years to recent, with metamorphic grade depending on the age and host of the rock type.