Travel Reference
In-Depth Information
For more than a century, deciphering the tangled, complicated mixture
of rocks that make up western North America has been the career choice (or
fate) of hundreds of the best earth scientists. They have needed to be smart:
The variety of assemblage and style seemed incomptehensihle for a long
time. The emergent theory of plate tectonics—and especially the new tool
of terrane analysis using paleomagnetism—seemed at last to offer a way out
of this morass. The observed direction of northwatd tectonic movement in
the present-day California coast region supplied a key clue to how the coast
had formed. Earth scientists began to wonder if much of the west coast of
North America had not formed far to the south, as small islands or subcon-
tinents, and then become accreted onto the continent. In the early 1970s,
teams from Canada and the United States began sampling various rock bod-
ies for paleomagnetism in order to test such ideas. These data eventually be-
came the primary weapons in a war pitting the geophysicists, armed with
their paleomagnetic information, against the many geologists who believed
that plate tectonic models requiring large-scale transport of rock bodies over
distances as much as several thousand miles were not necessary to explain
the complicated geology found in western North America.
The opening shot was fired in 1971, when Robert Tessier and Merl
Beck of Western Washington State University published paleomagnetic
data from the volcanic rocks making up Mt. Stuart, a forbiddingly high peak
in the North Cascades of Washington State. Compared with the largest of
the Cascade mountains, such as Mt. Rainier, or the nearby Mt. Baker (which
is still an active and exceedingly dangerous volcano), Mt. Stuart is far more
ancient, and it is "extinct." It has been dated repeatedly, using sophisticated
radiometric dating techniques, and all measures yield a Middle Cretaceous
age of about 100 million years ago. The dispute about Mt. Stuart is not about
its age but about where it was formed.
The pioneering work hy Tessier and Beck resulted in a startling discov-
ery: They found that Mt. Stuart was made up of rocks seemingly solidified at
a latitude far to the south of its present position. If the paleomagnetic results
were correct, then the gurgling, bubbling, molten magma that 100 million
