Geology west of the Melones Fault between the Feather and North Yubarivers, California

Abstract

Petrologic and structural studies of metamorphic and igneous rocks innorthern part of the western metamorphic belt of Sierra Nevada aredescribed. They extend (eastward) the area covered by earlier workdone in the Pulga and Bucks Lake quadrangles (Professional Paper 731),around the Middle and South forks of the Feather River (ProfessionalPaper 920), and in the Berry Creek Quadrangle (Professional Paper1027). The Melones Fault separates the continentally derived quartziteand schists of the Silurian Shoo Fly Formation on the east fromoceanic metachert and phyllite of the Pennsylvanian CalaverasFormation on the west. Metavolcanic rocks interbedded withmetasedimentary rocks of the Calaveras Formation are mineralogicallysimilar to metavolcanic rocks of the Franklin Canyon Formation in thewestern part of the area. Three new chemical analyses, together withthirteen analyses previously published, confirm earlier indicationthat the metavolcanic rocks of the Franklin Canyon Formation have thechemical characteristics and trace-element content of an earlyisland-arc-type tholeiite and andesite-sodarhyolite suite.Metamorphism in most parts of the study area was in the border zone ofthe greenschist and epidote amphibolite facies.--from the NewPublications of the Geological Survey, December 1981.

16 samples from this reference