The Cedars ultramafic mass is a mantle fragment that consists of partially serpentinized spinel harzburgite and dunite. Compositional layering and a chromite lineation define a penetrative metamorphic foliation that almost certainly formed in the upper mantle. Although detailed petrofabric and mineral chemistry are presently lacking, it seems reasonable that the Cedars peridotite represents a slice of mantle tectonite that once formed the base of the Coast Range ophiolite, and not an abyssal peridotite tectonically emplaced within the Franciscan accretionary prism.
Additional publication details
USGS Numbered Series
The Cedars ultramafic mass, Sonoma County, California
U.S. Geological Survey
Geology, Minerals, Energy and Geophysics Science Center
iii, 13 p.; maps col.; Plate: 1 Sheet: 15 x 15 inches