Dike emplacement and deformation in the Donner Summit pluton, central Sierra Nevada, California

Abstract

Late-stage magmatic activity in the Mesozoic Donner Summit pluton has produced several generations of well-exposed igneous dikes. The emplacement and deformation of the dikes occurred while the pluton was still partially molten. Dilation and shear displacement of the dikes and the geometry of the dikes in the field yield information about the mechanism and models responsible for dike emplacement and deformation. Mafic enclaves, which are consistently cross-cut by dikes, suggest that a slip patch mechanism can explain localized shear offset along dikes. Inelastic zones of deformation at the dike tip, where dike-parallel fractures form, indicate that some dikes created their own fractures as they grew and propagated through the pluton. Measurements of dike tip profiles show that a Dugdale-Barenblatt model of fracture mechanics is applicable to dikes and fractures, because the granite behaved inelastically independent of temperature and pressure.