Publication Date

Summer 2024

Degree Type

Thesis

Degree Name

Master of Science (MS)

Department

Geology

Advisor

Robert Miller; Jonathan Miller; Ellen Metzger

Abstract

Field, petrographic, and geochronologic analyses were conducted for five Cretaceous plutons in the North-Central Sierra Nevada batholith to better understand their construction, emplacement, and deformation histories. All the plutons in the study area were constructed incrementally, but timing and degrees of mixing between increments vary. The lack of internal contacts and heterogeneity in the interiors of the Stanislaus Meadow and Ebbetts Pass plutons suggest that there were sizeable magma chambers where there was thorough mixing of increments. The West of Elbow, Lookout Peak, and Kinney Lakes plutons were constructed from small batches of magma based on their textural and compositional heterogeneity. Plutons in the study area were emplaced via multiple emplacement mechanisms including stoping and assimilation, ductile flow, and magmatic wedging. Direct evidence for roof uplift, floor depression, or dilation by faults is absent in the plutons. NW-striking magmatic foliations in the Stanislaus Meadow, Ebbetts Pass, and Lookout Peak plutons are discordant to contacts and subparallel to regional foliation, recording regional strain. Margin-parallel magmatic foliations reflect complex internal magmatic processes. Solid-state structures include foliations and lineations, which formed by regional tectonic strain. The origin of widespread small-scale ductile shear zones in the Lookout Peak tonalite remains enigmatic. Overall, magmatic structures and construction processes in the studied plutons are similar to those elsewhere in the Sierra Nevada batholith.

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