Tectonics of the Sierra Nevada “The grandeur of these forces and their glorious results overpower me, and inhabit my whole being.” John Muir

Geography of the Sierra Nevada Sierra Nevada Photos, 2010 Photo edited from Dr. Bartley

Physical Characteristics of the Sierra Nevada North South Sierra Nevada Photos, 2010 Satellite photo of eastern Sierra Nevada S N

Sierra Nevada Structure and Motion Composition Granite solidified below the surface between 210 ma and 80 ma. Cooled magma chamber to the Sevier Orogeny Some metamorphosed rock is preserved on the tops of mountains as “roof pendants” Currently Motion of the Sierran Microplate is independent of the stable portions of the North America plate Motion relative Pacific Plate is NW 38 mm/yr Relative to the North America plate NW 11-13 mm/yr Active faulting on the east (steep) side of Sierra Nevada Figure 1. Oblique Mercator projection of western Cordillera about preferred Sierra Nevada–North American Euler pole of Argus and Gordon (2001). Direction of instantaneous Sierra Nevada–North American motion is vertical everywhere in projection. Strike-slip faults of Walker Lane belt are subparallel to Sierra Nevada–North American motion; normal faults strike ∼45° clockwise of that motion; and major graben and zones of extension are located in areas where locus of deformation along eastern Sierra is steps eastward in releasing geometry (Quaternary faults modified from Jennings, 1994). MTJ—Mendocino triple junction; SEGP—subducted southern edge of Gorda plate; CB—Cape Blanco; ICF—Inks Creek fold belt; HC—Hat Creek graben; A—Lake Almanor structural basin; MV—Mohawk Valley; HL—Honey Lake fault; T—Lake Tahoe basin; C—Carson Valley; LV—Long Valley; SNFFS—Sierra Nevada frontal fault system; I—Independence fault; OV—Owens Valley; IWV—Indian Wells Valley; ECSZ—Eastern California shear zone; DV—Death Valley Unruh J et al. Geology 2003;31:327-330

Formation of the Sierra Nevada Uplift Processes Farallon Plate Subduction 210-80 ma Sevier/Laramide orogeny Batholith formation Several hundred plutons of various sizes, ages, and isotopic signatures Delamination of Sierra Nevada Microplate 2-3 ma (10 ma?) Tilting of batholith block to west Variation in Moho depth along Sierra Nevada (~42 km in North to 30 km in South) Disappearance of the Moho south and east of Fresno, CA Low gravity anomaly in the southern Sierra Nevada associated with delamination Volcanic Activity Period of volcanic activity began 30 ma and continues today Zandt, et al.