EXAMINING PUMICES AND LAVA FLOWS FROM SOCOMPA VOLCANO IN THE CENTRAL ANDES

Socompa Volcano is considered one of the many large volcanoes found within the southern region of the Central Andes. Featured with, and around this volcano, are multiple pyroclastic fall and flow deposits (Holocene in age), lava flows, and domes. The aim of this study is to determine whether the Holocene post-collapse deposits (pyroclastic fall and flows) of Socompa Volcano are sourced from the same magma plumbing system, particularly: whether the plagioclase content and chemistry (along with hornblende and pyroxene content and chemistry) within the pumices correlate with the same plumbing system as the lava flows. Five samples of pumice (and samples of lava flows) have been collected from the pre-collapse lavas and pumice fall deposits, and analyzed using electron microscopy. This analysis was made for oscillatory plagioclase (which showed heavy sieving, slight resorption, and moderate-to-heavy fractures) in the pumice samples to obtain the weight percent of Anorthite present in plagioclase. Analysis was further conducted to determine Fe (ppm) and Mg (ppm) content of the oscillatory plagioclase. The maximum and minimum percentage of Anorthite found within the plagioclase was found to be 51% and 26%, respectively. The maximum and minimum Fe (ppm) was found to be 7144 ppm and 773 ppm, respectively, and Mg (ppm) was 2274 ppm and 0 ppm, respectively. There were two populations of plagioclase: normal and reverse oscillatory zoning plagioclase crystals, showing and interpreted as: magma mixing (causing sieve, and resorption, if hot enough), and magma cooling/ rapid cooling (overgrowths/fractures) developed the plagioclase.