Margin processes

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, and the granite batholiths in the Sierra Nevada range were emplaced.

Perspective view from the west of Hydrate Ridge off Oregon, where methane hydrates have been found Image © 2001 MBARI

Perspective view from the west of Hydrate Ridge off Oregon, 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.

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Hydrates and seeps

In the late 1970s, oceanographers were astounded to discover flourishing communities of animals clustered around deep-sea hydrothermal vents.
Map of the California Borderland, which is a broad area of basins and ranges with some islands off Southern California.
Map © MBARI 2006

California Borderland

The geologic history of the region offshore of Southern California iis complicated by the fact that it is largely submerged, heavily sedimented, and many of the rocks from which interpretations have been made were probably erratics.


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