Genesis of Mylonite and Structure of Francis Peak, Wasatch Mountains, Utah

Abstract

This thesis focuses on progressive deformation and mylonite formation from three common protolith rock types, layered gneiss, amphibolite and granitic rock. Protolith rock types and deformed equivalents were sampled in · the Farmington Canyon Complex on Francis Peak in the northern Wasatch Mountains of Utah. Genesis of mylonitic foliation and lineation was promoted by grain-scale processes such as recrystallization, strain, solution transfer, metamorphic reaction and fluid influx. Despite the extreme textural transition that takes place during mylonitization, protolith rock type can often be identified even after complete recrystallization. Geometric and kinematic field data were used to constrain the tectonic history of the rocks and to construct a model for the development of structures associated with the mylonites. Mylonitization probably took place during an obscure Proterozoic deformation or the Cretaceaous Sevier Orogeny, although kinematic data suggest that the former is more likely.