DYNAMICS AND TIMESCALES OF MAGMA RESIDENCE BENEATH AT SOCOMPA VOLCANO, SOUTHERN CENTRAL ANDES, CHILE

Socompa Volcano, located in the southern segment of the Central Andes, is one of the largest Quaternary volcanoes in the Central Andes. The edifice consists of lava flows, domes and pyroclastic fall and flow deposits with the dominant feature being a large landslide scar opening to the north-northwest. Within the landslide scar, Holocene post-collapse deposits date to less than 6 ka. A widespread Plinian fall deposit blankets the southern flank of the volcano. Here, we present new whole rock and mineral major and trace element data and zircon U-Th disequilibria ages from five single pumices from the fall deposit. We compare these data to the pre-collapse domes and lavas on the southern flank. New zircon ages of pumice are older than eruption age and show a range in crystallization age from approximately 285±147 ka to 1.7±9.3 ka and a weighted mean crystallization age of 45.8±6.9 ka. In comparison, lavas and domes have older zircon crystallization ages ranging with the youngest zircon at ~100 ka. Eruption ages for the same lavas underlying the fall deposit range from 22-30 ka. Aluminum in hornblende temperatures and crystallization depths in the domes and lavas suggest multiple chambers at 4-5 km and 10-15 km with temperatures ranging from 850-1000°C. The youngest pre-eruptive dome and the fall pumice hornblende suggest homogenization of the magma chamber in at 10-15 km depth and more consistent temperatures between 950-1000°C. Zircon and amphibole suggest that storage was at near solidus or sub solidus conditions after crystallization, with several periods of crystallization and reactivation leading to eruption. Hornblende dissolution (from heating), crystallization (from cooling), and storage repeated at different levels of the magmatic storage system. Continuous recharge into the chamber acts as the main reactivator of the reservoir and provides a critical role in continuous crystallization of zircon. Therefore, zircon reveals processes ranging from >100 k.y. to short term storage in response to recharge events. Overall, we suggest a model for the ongoing construction of a silicic magma storage complex beneath Socompa. Zircon ages suggest that accumulation of this complex is entirely Quaternary in age.