The Architecture of the Southern Puna Magmatic System: Integrating Seismic and Petrologic Observations With Geochemical Modeling

Improvements in geochemical, petrologic, and geophysical methods and data have led to a paradigm-shift in understanding magmatic system architecture away from isolated magmatic chambers toward transcrustal "mushy" magmatic systems. Geochemical and petrologic studies indicate that magma storage and differentiation occurs over a range of depths throughout the crust, while geophysical techniques delineate in situ spatial distributions of melt at similar scales. However, seismic properties are nonunique with respect to composition and melt percentage, and must be integrated with geochemical observations to better understand the architecture and chemical evolution of magmatic systems. The southern Puna Plateau represents a locality where extensive geochemical and seismic data can be combined to investigate the role of depth-dependent processes in generating compositionally diverse volcanism. By combining geochemical modeling with seismic images of shear-wave velocity and attenuation, we find that magma storage and differentiation occurs predominantly at two depth ranges: (a) near the base of the crust (>40 km), where shear-wave velocities are anomalously slow compared to what is expected (<4.0 km/s) and geochemical signatures indicate fractional crystallization and crustal assimilation in the garnet stability field, and (b) in the mid-crust (∼20 km) beneath the Cerro Galan Caldera, where shear-wave velocities necessitate the presence of melt (∼2.7 km/s) and europium (Eu) anomalies indicate low-pressure differentiation. These geochemical and seismic results provide evidence for multi-level melt evolution and are consistent with petrological features of exposed arcs, whose transcrustal architecture is characterized by discrete and compositionally evolved intrusive bodies in the mid-crust and a compositionally heterogeneous lower crust.