Publication Date

Spring 2013

Degree Type


Degree Name

Master of Science (MS)




Robert B. Miller


Foliation, Magmatic, Pluton, Structural Geology, Yosemite

Subject Areas



The 103-98 Ma El Capitan and Taft granites and the ~97 Ma Yosemite Creek Granodiorite intrude plutonic and metasedimentary rocks in the central Sierra Nevada batholith. The El Capitan Granite and Yosemite Creek Granodiorite are divided in this study into several texturally and compositionally distinct units, whereas the Taft Granite is relatively homogeneous. Injection of a few large increments of magma or many increments intruded close in time probably formed small (2 km3) to large (≥20 km3 for Taft Granite) chambers in the Yosemite Valley Suite and parts of the Yosemite Creek Granodiorite. Units of the Yosemite Creek Granodiorite that intruded as steep, narrow sheets probably solidified shortly after intrusion. Emplacement of Yosemite Creek magmas was facilitated by wedging aside of host rock, stoping, and possibly ductile flow. The plutons have steep, dominantly NE-striking magmatic foliations, some of which are discordant to contacts and record regional strain that contrasts with the regional strain field interpreted from plate kinematics. The major Mt. Hoffman shear zone comprises thousands of narrow (meter-scale) NE-striking, reverse-slip ductile shear zones that deformed the eastern part of the El Capitan Granite prior to intrusion of the Taft Granite. Other sizable solid-state shear zones of this age in the region strike NW, and thus the regional strain field was likely heterogeneous from 103-98 Ma.

JOHNSON_.PDF (23085 kB)