Thermodynamic analysis of minerals from Cerro Galan and Cerro Blanco, NW Argentina
Luna Gonzalez, Joao Carlos
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Cerro Galan and Cerro Blanco are two large Plio-Pleistocene calderas from the Andes of NW Argentina located within 120 km of each other. Large ash flows erupted from both volcanoes are relatively-well preserved and minimally eroded. Multiple sections of ignimbrites from both volcanoes were sampled and form the basis of this study. Their mineralogical assemblage— biotite + plagioclase + sanidine + Fe-Ti oxides + quartz + apatite—makes them well suited for the estimation of pre-eruptive intensive variables (temperature, pressure) in large silicic sub-volcanic magma chambers. The presence of minerals that incorporate F, Cl, and OH such as apatite and biotite also makes them ideal for studying the relationship between these fluids species as function of vertical location and temperature within the pre-eruptive magma chamber. Results indicate both calderas were at a minimum pressure of 2 kbar based on an equilibrium temperature of about 700 0C and 4% H2O saturation.