LINKING VOLATILE BEHAVIOR AND ERUPTIVE STYLE IN CENTRAL ANDEAN VOLCANOES: THE CASES OF LASCAR AND UTURUNCU

Advances in knowledge about the compositional behavior of magmatic apatite make it a relevant tool for modeling volcanic plumbing systems. Provided a temporal framework, apatite records variations in budget and behavior of volatiles throughout eruptive stages and records the changes in isotopic signatures of pre-eruptive magma. We present the first stages of a study that takes advantage of these qualities to unravel how mass-transfer processes modify the content and behavior of volatiles in the pre-eruptive plumbing systems of Lascar volcano and Cerro Uturuncu (Central Andean Volcanic Zone), consequently defining their eruptive styles.

Individual crystals from samples of different eruptive stages of Lascar and Uturuncu have been picked and analyzed through LA-ICPMS and SHRIMP-RG to obtain their chemical composition and isotopic signatures. By using theoretical partition coefficients, their volatile budget (S, Cl) and isotopic signature (⁸⁷Sr/⁸⁶Sr) will work as a proxy for those of pre-eruptive magma. Variations in isotopic signatures throughout the samples will allow the identification and quantification of mass-transfer processes occurring in the magmatic reservoir(s) feeding these volcanoes. The temporal framework of the samples will allow the correlation of these processes to changes in budget and behavior of magmatic volatiles and the eruptive style registered in volcanic stratigraphy.

Deducting a comprehensive model from this data will contribute to further the understanding of eruptive behavior of Andean stratovolcanoes, providing new constraints to the limit conditions in which volatiles define eruptive style in continental arc volcanism settings and reaffirming apatite as a versatile tool for the characterization of igneous petrogenetic processes.