Margin processes

Sea star Asthenactis fisheri on heavily manganese-coated talus on the Patton Escarpment off Southern California.

Processes of a tectonically-active continental margin

The continental margin of California was a subduction zone until the mid-Cenozoic. The Farallon tectonic plate subducted under the North American plate and was eventually consumed, sedimentary and crustal material was accreted to the continental margin (now exposed in the Patton Escarpment in the California Borderland), and the granite batholiths in the Sierra Nevada range were emplaced.

Perspective view from the west of a map of Hydrate Ridge off Oregon, in the accretionary prism of the Cascadia Subduction Zone and where methane hydrates have been found.
Image © 2001 MBARI

The tectonics of central California changed with the passage through the area of the triple-junction now off Mendocino; subduction is still occurring off Oregon and Washington. Now our continental margin is being deformed by the generally strike-slip motion of the San Andreas fault, as the Pacific plate moves north-west relative to the North American plate, carrying the sliver of coastal California with it. Adjustments to the motions of the plates have occurred, which in some places generated tensional forces and subsequent volcanic activity (see the continental margin seamounts page), and in other places generated compressional forces, such as are currently uplifting the Santa Cruz mountains.

Related to the active tectonics of the area, are the erosion that shapes the Monterey canyon and the seepage of methane and sulfide-rich fluids that influences the biology. Our group has been involved in these studies, despite there not being a volcanic component. Much more information about these processes can be found in the related links below.