Petrogenesis of the pine flat complex of the sierra nevada: a geochemical investigation of differentiation within the crust

The mafic to felsic transition during pluton emplacement has been a long debated magma evolution process, resulting in competing models for granitic formation. Pluton assemblage within the crust is thought as a simplified product of crystallization but interactions with crust and surrounding plutons during emplacement remain unclear. General pluton studies of the Sierra Nevada Batholith focus on these interactions using single high-elevation plutons, leaving uncertainty to low-elevation development and potential unifying processes. The Pine Flat Complex (PFC), located in the lower foothills of California’s Sierra Nevada exposes basaltic to granitic rocks. Guided by competing crustal formation models, the PFC resembles the Guadalupe Igneous Complex (GIC; 125 km northwest) in field and geochemical observations suggesting similar processes spanning a larger landscape. Both the PFC and GIC have interlayered sheets of mafic, felsic, and hybrid rocks. Batch fractionation models indicate intermediate compositions were a product of magma mixing due to convection of mafic magma injecting into pre-existing wall-rock, while granites were produced by crystal-melt separation. Sr/Y “depthometer” estimates depth of melt ~35 km and is supported by similar depths of fractionation using La/Yb and Dy/Yb ratios. The PFC’s feeder system may lead to the adjacent Bass Lake Tonalite pluton based on similar geochemical data. Application of the PFC’s petrogenesis helps contribute further understanding.