PROLONGED 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 k.a. A widespread Plinian fall deposit blankets the southern flank of the volcano. Here, we present new whole rock and mineral trace element data and twenty zircon ages from U-Th disequilibria and U-Pb from as single pumice 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,-1.7 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 covered by the fall deposit range from 22-30 ka. Additionally, large plagioclase phenocrysts in the lavas show complex zoning patterns with multiple resorption surfaces reflecting prolonged storage and multiple recharge events. Plagioclase phenocrysts from the pumices are smaller with less complex zoning. Zircon and plagioclase data suggests that the pre-collapse lavas and domes erupted from Socompa record a protracted magma storage while explosive products are sourced from different part of the chamber, and are stored for shorter time periods, but overlap with the storage of the effusive products.