Structure, emplacement and lateral expansion of the San José tonalite pluton, Peninsular Ranges batholith, Baja California, México

The 108 km² San José pluton forms part of the Jurassic to Cretaceous Peninsular Ranges batholith of northern Baja California, México. The pluton was formed by three nested, southward-migrating intrusive pulses, and the internal contacts between them indicate juxtaposition while the adjoining pulses were magmas. SHRIMP U-Pb zircon data indicate that the entire pluton was emplaced in less than 4.4 m.y.; ages of the individual pulses cannot be separated at the 95% confidence interval, owing primarily to low uranium content of zircon. Detailed structural data and geologic mapping are consistent with a component of asymmetrical, lateral expansion at the site of emplacement. The direction of maximum lateral expansion may have been controlled by thermal, compositional and resulting rheological gradients in the surrounding wall rocks. A carapace of predominantly solid-state deformation marks the northern two-thirds of the pluton, and the early stages of this fabric may have formed in the presence of a small amount of melt. Lack of evidence for syn- to post-emplacement regional ductile deformation around the pluton suggests that this carapace was deformed during the lateral expansion of the pluton.