Master of Science (MS)
Robert B. Miller
ductile shear zone, Keiths Dome, Lake Tahoe, Mount Tallac, Nevadan orogeny, pluton
Jurassic (Keiths Dome) and Cretaceous (Echo Lake, Glen Alpine) plutons and their host rocks were investigated, and structural and petrographic analyses were conducted, to elucidate the nature and timing of pluton construction and emplacement, deformation, and related tectonic regimes. Evenly distributed enclaves and a lack of internal contacts suggest pluton construction via thorough mixing of multiple increments of magma. Ductile flow of conglomerate host rocks, stoping of volcanic host rocks, and possibly other processes, facilitated emplacement. In Cretaceous plutons, margin-parallel magmatic foliations may record internal processes, whereas the Keiths Dome pluton contains foliations that are discordant to contacts and likely record regional strain. The Keiths Dome pluton contains NW-striking, steeply dipping ductile shear zones, and steeply dipping microdiorite dikes that are deformed by some shear zones. The inferred strain field from foliation, lineation, dikes, and ductile shear zones is one of regional transpression that likely changed or weakened prior to intrusion of the Cretaceous plutons. Emplacement of the Keiths Dome pluton and subsequent ductile shear may have occurred during the Late Jurassic Nevadan orogeny, as other syntectonic dike swarms in the Sierra Nevada batholith are 158-148 Ma. Geochronologic data are needed to further constrain the timing of deformation.
Clay, Pamela Jamie, "Structure, Construction, and Emplacement of Jurassic and Cretaceous Plutons in the Keiths Dome-Echo Lake Area, Southwest of Lake Tahoe, California" (2014). Master's Theses. 4492.