Post on 23-Feb-2016
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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.