PETROGRAPHIC OBSERVATIONS OF THE WOLF BAR AMPHIBOLITE

Rocks exposed along the American River near Auburn, California, consist of greenschist-facies ophiolitic and sedimentary material that have been previously interpreted to be part of the Sierra Nevada Central Belt. These rocks are bounded on the east by a narrow strip of mafic amphibolite termed the Wolf Bar Amphibolite (WBA). Previous work published in an MS thesis describes the WBA as a foliated mafic amphibolite consisting of hornblende, plagioclase, and titanite with rare rutile inclusions, with an age of about 196 Ma based on Ar-Ar geochronology. These initial descriptions of the amphibolite appear to have come from a particularly homogeneous subset of WBA rocks exposed along trails above the river.

In this poster we present new petrographic and field evidence from the Wolf Bar Amphibolite exploring the lithological heterogeneity of the units. At exposures along the American River the amphibolite consists of strongly foliated rock that displays compositional layering between lighter and darker domains along with felsic blobs that indicate partial melt of the rock. Mafic dikes crosscut the foliation, filling irregular brittle fractures, and also appear to be metamorphosed to amphibolite facies. These rocks may be analogous to metamorphic sole rocks found elsewhere in the Central Belt.