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

Photo edited from Dr. Bartley

Sierra Nevada Photos, 2010

Satellite photo of eastern Sierra Nevada

S

N

North South

Sierra Nevada Photos, 2010

Physical Characteristics of the Sierra Nevada

Sierra Nevada Structure and MotionComposition• 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 Unruh J et al. Geology 2003;31:327-330

Formation of the Sierra Nevada

Uplift ProcessesFarallon 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.