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Exotic Terranes
Western North America

Submitted by M. S. Pachuta

Semester Project: ES 767 ~ Dr. James S. Aber, Instructor

Emporia State University, Emporia, Kansas

Spring, 2002


The Pacific Northwest is made up of some of the most exotic terranes found in North America. The geologic history of the terranes and overlap assemblages is highly complex because terranes fragment and disperse after impact, and they react to the geologic processes they are helping to create. The western margins of British Columbia and Oregon, and most of Alaska, Washington and California are an amalgam of accreted crust. This project presents a time line for the discovery and understanding of exotic terranes, a description of these geologic structures, and a time line for the geologic history of the western boundary of the North American continent.

The goal is to create interest and provide accurate information without intimidating or overwhelming terminology. And since as much as 25% (some geologists think perhaps closer to 30%) of North America's land mass is made up of these microplates, knowing something about them would be a good thing! Suspect terranes differ from exotic terranes in that their place of origin cannot be positively established. Their inclusion, however, increases the amount of western North America attributed to accretion to 70%! Highlighted words link directly to the glossary list.

It should be noted that sizable accretion has occurred on the eastern and southeastern North American continental boundary, in other areas along the Pacific Rim, and throughout the planet over time, continuing as part of the dynamic Earth processes.

Our discussion will focus on the western boundary of the North American continent.

Glossary List