Volcanologic and petrologic evolution of Antuco-Sierra Velluda, Southern Andes, Chile

Whereas Sierra Velluda erupted basaltic andesitic to andesitic (53.5 to 58.7 wt% SiO2) lavas, during the last expansion of glaciers between ~ 130 and 17 ka, Early Antuco erupted a wider spectrum of lavas, ranging from basaltic andesite to dacite (52.0 to 64.5 wt% SiO2). Notably, eruptions following the last glacial termination at 17 ka produced basalts and basaltic andesites (50.9-53.7% SiO2), and following the 6.2 ka cone collapse they have been exclusively olivine basalt (50.9-53.0% SiO2) with > 5 wt% MgO. Thermodynamic and trace element modeling suggests that lavas from Sierra Velluda and Early Antuco reflect extensive fractional crystallization of parental basaltic magmas with low water content (~ 1 wt%) at pressures between 0.9 and 1.5 kbar. In contrast, eruptions following rapid deglaciation tapped asthenospheric mantle-derived basalt that has been extensively modified by assimilation of partial melts of lower crustal rocks.