GEOCHEMICAL ANALYSIS OF LASCAR VOLCANO: DIFFUSION CHRONOMETRY, MINERAL CHEMISTRY, AND TRACE ELEMENT CHEMISTRY OF ZIRCON AND PLAGIOCLASE

Lascar volcano is the most active volcano in the Central Volcanic Zone of the Andean Cordillerain, with 36 Holocene eruptions including a VEI 4 eruption in April 1993 which produced bimodal pumices. Activity has not been consistent throughout time, and is therefore the processes behind it are poorly understood. Lascar volcano has cyclic behavior and has had four stages of activity, each of which had a unique eruptive style and product composition. Stage I (<43 ka) had primarily mafic andesite lavas that erupted effusively from a stratocone. Stage II (>26.5 ka) had a dome building event ESE of the original vent and produced the Soncor deposit, which is the largest that Lascar has ever produced. There was then a period of quiescence, after which were the Tumbres pyroclastic flow deposits; the current Stage IV eruptions are explosive in nature and produce lava domes, pyroclastic flows, and pumices. The aim of this project is to determine if the bimodal nature of the pumices is caused by rejuvenation of magma into Lascar’s reservoir via diffusion geochronometry of plagioclase and zircon and trace element chemical analysis, and if that injection triggers volcanic activity. If so, that would explain the cyclic nature and dynamic compositions that Lascar exhibits. Preliminary mineral chemistry suggests that magma mixing is more prevalent in the system than originally hypothesized, warranting further investigation into this unique composite cone.