REGIONAL DEFORMATION OF THE SIERRA-NEVADA, CALIFORNIA, ON CONJUGATE MICROFAULT SETS

Strike slip microfaults are pervasive throughout the granitic rocks of the E Sierra Nevada. Offsets typically range from less than a millimeter to several tens of centimeters but exceed 100m in some places. The spacing between microfaults varies from a few tens of centimeters to a few tens of meters throughout much of the high Sierra Nevada. Many of these microfaults are loci of slickensided, compact fault gouge, and they are commonly mineralized by quartz veinlets with minor amounts of epidote, chlorite, and rare sulphide minerals. The microfaults are oriented in two nearly vertical conjugate sets: a N to SE striking set showing right lateral offset and an E to NE striking set showing left lateral offset. Microfaults with left lateral offset are more common than microfaults with right lateral offset. Most lineaments visible on aerial photographs are microfaults. The age of this microfaulting is not precisely known. It developed after consolidation of the youngest granitic plutons in the Sierra (79Ma BP) and is known to cut a late Miocene volcanic dike in one area. Slickensides along the mirofaults are sub-horizontal but show a slight (about 3o) W plunging average inclination, suggesting that much of the deformation occurred prior to the W tilting of the Sierran block in late Tertiary time.- Authors