Franciscan Assemblage

The Franciscan Assemblage is a geological term for an accreted terrane of heterogeneous rocks found on and near the San Francisco Peninsula. It was named by geologist Andrew Lawson who also named the San Andreas Fault which bounds the Franciscan Assemblage.

Also known as the "Franciscan Formation," "Franciscan Series," "Franciscan Group," "Franciscan assemblage," or "Franciscan Complex," it includes altered mafic volcanic rocks (greenstones), deep-sea cherts, greywacke sandstones, limestones, serpentinites, shales, and high-pressure metamorphic rocks, all of them faulted and mixed in a seemingly chaotic manner.

It forms the major component of the Pacific Coast Ranges of California.

Wentworth and others (1984) interpreted the juxtaposition of the Franciscan Assemblage and the section consisting of the Coast Range ophiolite and the Great Valley sequence to have happened through landward movement of the Franciscan Assemblage as a tectonic wedge.

References

*Wentworth, C. M., Blake, M. C. Jr., Jones, D. L., Walter, A. W., and Zoback, M. D. 1984. Tectonic wedging associated with emplacement of the Franciscan assemblage, California Coast Ranges. In Blake, M.C., ed., Franciscan geology of northern California. Pacific Section, Society of Economic Paleontologists and Mineralogists, Field Trip Guidebook 43, p. 163-173.

External links

* [http://menlocampus.wr.usgs.gov/50years/accomplishments/franciscan.html US Geological survey]
* [http://www.johnmartin.com/earthquakes/eqsafs/safs_827.htm JohnMartin.com]
* [http://www.nps.gov/archive/prsf/geology/geology.htm NPS: Geology of the Golden Gate]