Magma mingling/mixing in a heterogeneous, multi-pulse magmatic system: An example from the Jackass Lakes pluton, central Sierra Nevada batholith

The Jackass Lakes pluton, central Sierra Nevada batholith, has been the focus of several studies investigating the emplacement and temporal evolution of this heterogeneous intrusion. Detailed field mapping in a central domain of the pluton identified eight distinct units (diorite to granite). Extensive mingling features within and between units indicate that magma mingling was an important process throughout the evolution of this magma chamber. A number of microstructures common to mixed magmas were identified during petrographic examination. Furthermore, linear trends observed from whole-rock and trace element geochemistry suggest mixing was involved, at least locally, during chamber construction. The compositional variation suggests that the chamber formed as a result of multiple pulses of magma at uniform shallow levels, as indicated by hornblende-plagioclase thermobarometry pressure-temperature estimates of 2.8 kilobars and 670°C. These findings indicate that mingling and mixing occurred throughout the evolution of the pluton, likely during ascent of magma pulses.