TRACKING MAGMATIC PROCESSES USING ZIRCON TRACE ELEMENT COMPOSITION AT CERRO UTURUNCU, BOLIVIA

Zircon trace element compositions from Cerro Uturuncu present a unique opportunity to track magmatic processes and magma storage temperatures and timescales. Uturuncu resides in the back arc of the Central Volcanic Zone (CVZ) in Chile and is unique compared to similar age and composition arc-front equivalents. Whole rock trace element contents suggest that Uturuncu is derived from a garnet-free, plagioclase-stable, radiogenic source despite the depth of the subducted slab being greater than 150 km. Here we present zircon trace element contents from Uturuncu lavas and compare these data to zircons from large-volume domes along the arc-front and Volcan Ollagüe to determine the conditions of magma storage during zircon crystallization. Uturuncu zircon show little variation between samples spanning 750ky and generally reflect the whole rock signatures compared to the arc front. Large volume Altiplano Puna Volcanic Complex (APVC) domes, including the Chao Dacite, show unique zircon trace element trends and consistently have higher Hf contents and Th/U, U/Yb and Ce/Yb ratios, and lower Gd/Yb ratios. Titanium-in-zircon temperatures are variable between samples ranging from 650°C to over 900°C, are relatively consistent with a sample. Zircon temperatures typically surpass zircon saturation temperatures, suggesting that zircon crystallized and was entrained in a hot zone within the magmatic system. Trace element ratios suggest a transition from a garnet signature to a titanite/apatite fractionation and cooling signature with time. Ollagüe zircons show similar trends but the correlation with age and temperature. Collectively, Uturuncu zircon trace element data suggests that magma feeding Uturuncu lavas was stored and rejuvenated periodically. Storage conditions show similarities in trace element signature with both other CVZ arc front volcanoes and the APVC domes. We conclude that Uturuncu storage conditions and magma sources are initially more similar to the arc front composite volcanoes than the APVC ignimbrites and domes, but transition to become a hybrid between these two end members.