Geology of British Columbia - Terrane Theory

Terrane Theory

Terrane theory was first proposed by Jim Monger of the Geological Survey of Canada and Charlie Rouse in 1971 as an explanation for a set of fusilinid fossils found in central British Columbia. Rather than use facies changes or seaways (which were common explanations at the time), the two geologists proposed that the fossils in question had been part of an assemblage of rocks that had migrated across the Pacific Ocean to their present location. This theory was then developed by Porter Irwin and Davy Jones of the US Geological Survey to its common definition of "fault bounded regional geologic entities, each characterized by a different geologic history than its neighbours".

Terranes are most commonly associated with different tectonic elements such as island arcs, volcanic plateaus, subduction zones, continental margins, mid-oceanic ridges and continental fragments. These terranes are gradually joined together by elements such as overlap assemblages and stitching plutons and are then accreted to the continent. In some cases, a terrane can contain multiple tectonic elements. The Cache Creek Terrane is composed of a massive carbonate component, an oceanic floor component and a subduction mélange component.