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.