Download Tanya Shavalia The Farallon and Juan de Fuca Plates leaving only

Tanya Shavalia
Bunge and Grand, Nature, May 2000
The Farallon and Juan de Fuca Plates
Much of the geology of western North America has
been shaped by the interaction of the Kula,
Farallon and Pacific plates. However,
reconstructing plate motions beyond the Mesozoic
period is extremely difficult due to plate loss by
subduction. The Farallon plate is thought to have
been adjacent to western North America from 85 to
56 million years ago, and its low angle subduction
may be partially responsible for the CretaceousEocene Laramide Orogeny (Bunge, 2000). The
interaction of the Farallon-North American plate
boundary is still occurring today in the form of the
Juan de Fuca microplate subduction system,
however, towards the end of its lifespan, the
Farallon plate was broken up to crate the Juan de
Fuca, Rivera and Cocos plates. The remainder was
entirely subducted under the North American and
Caribbean plates. So, the Pacific-North American
plate boundary began to dominate the western U.S.
This diagram
illustrates the
shrinking of the
Farallon Plate, as
it was subducted
beneath the North
American Plate,
leaving only the
present-day Juan
de Fuca, Rivera,
and Cocos Plates
as remnants.
http://pubs.usgs.gov/publications/text/Farallon.
Based on evidence from seismic tomography, remnants of the Farallon plate are thought
to still reside in the upper mantle beneath the North American continent, and Usui et al
(Geology, 2003) posit that eclogites found in the Colorado Plateau may have originated
as fragments of the subducted Farallon plate.
The Juan de Fuca microplate system is located
between 40 and 52 deg. N latitude, and
comprises part of the Pacific "Ring of Fire". It
subducts under the North American plate quite
slowly (~3cm/yr), producing the volcanic
Cascade Range, which has been active for 36
million years. Conversely, the Juan de Fuca /
Pacific plate boundary is divergent, resulting in
the formation of the Juan de Fuca Ridge, a broad
mountain chain ~500km long. The Pacific plate
moves in “strike-slip” motion with respect to the
North American plate, and the Mendocino triple
junction represents the point at which all three of
these margin types are in contact.
http://www.colorado.edu/GeolSci/Resources/WUSTectonics/PacNW/
juan_de_Fuca_general.html