Field, chemical, and physical constraints on mafic-felsic magma interaction in the Lamarck Granodiorite, Sierra Nevada, California
Field, chemical, and physical constraints on mafic-felsic magma interaction in the Lamarck Granodiorite, Sierra Nevada, California
Geological Society of America Bulletin (August 1987) 99 (2): 272-291
- acidic magmas
- California
- Central California
- composition
- fractional crystallization
- Fresno County California
- gabbros
- genesis
- geochemistry
- granites
- granodiorites
- hybridization
- igneous rocks
- intrusions
- least-squares analysis
- mafic magmas
- magmas
- major elements
- petrology
- phenocrysts
- physicochemical properties
- plutonic rocks
- properties
- rheology
- schlieren
- Sierra Nevada
- statistical analysis
- textures
- United States
- viscosity
- X-ray data
- Lamarck Granodiorite
Evidence of interaction between magmas of contrasting compositions throughout the crystallization of the Lamarck granodiorite is present in field relations, petrographic observations and major element compositions. The nature of magma interaction is largely a function of the viscosities of the end-members after they had thermally equilibrated. This model is adopted and extended to account for a wide range of initial compositions, T, water contents and crystal contents. Whether magmas mix as liquids, quench as enclaves, or crystallize as large intrusions that hybridize only locally with their host, depends on their rheologies and the manner in which rheologies change during interaction. Mingling is dominant in mixtures having low mass fraction of hot mafic magma at any initial T and crystallinity of the felsic magma. Hybridization becomes likely for large mass fractionation of mafic magma and/or as thermal and compositional contrasts between interacting magmas decrease.