Geology of the Inconsolable Range, east-central Sierra Nevada, Kings Canyon National Park and John Muir Wilderness, California: Magmatic emplacement and the dynamic evolution of composite intrusions

Igneous relationships within a portion of the east-central Sierra Nevada batholith (SNB) are investigated. Field data from the Inconsolable Range pertaining to the distribution of mafic and felsic rocks exposed in the composite Bull Lake Intrusion indicates that past paradigms for granitoid emplacement and compositional zonation observed within the SNB are largely incorrect. A new field-based hypothesis is developed to explain the emplacement of granitoids into the batholith with the simultaneous genesis of compositional variation and zonation that is more consistent with field data, fluid dynamic principles, and chemical data than past models. The resultant theoretical model suggests that magmas of disparate viscosities simultaneously ascend from source regions through common fractures and conduits within the upper crust. Minimization of flow energy dissipated by viscosity and the development of significant pressure differentials between the two discrete magmas undergoing dike emplacement results in lubrication of the higher viscosity magma by the lower viscosity magma to produce normally-zoned core-annular flow (magmatic encapsulation) as demonstrated in previous polymer extrusion studies, numerical modeling, and computational modeling. Thus, compositional zonation at a variety of scales may develop largely from magmatic encapsulation not post-emplacement chemical processes in essentially static, upper crustal magma chambers. Implications of this model are: (1) granitoids forming the SNB were emplaced through fractures and not primarily as diapirs; (2) encapsulated magmas emplaced via fractures inflated emplacement level magma chambers, and perhaps most importantly; (3) compositional zonation in igneous composites results from fluid dynamic processes not primarily from geochemical.