Storage conditions of the mafic and silicic magmas at Cotopaxi, Ecuador

摘要: The 2015 reactivation of the Cotopaxi volcano urges us to understand complex eruptive dynamics for better management a potential major crisis in near future. has commonly transitioned from andesitic eruptions strombolian style (lava flows and scoria ballistics) or nuees ardentes (pyroclastic ash falls) highly explosive rhyolitic ignimbrites (pumiceous pyroclastic flows), which entail drastically different risks. To interpret geophysical geochemical signals, magma storage conditions were determined via existing phase-equilibrium experiments that used starting materials chemically close andesites rhyolites. results suggest Cotopaxi's most mafic (last erupted products) can be stored over large range depth ~7 km ≥16 km below summit (pressure ~200 ≥400 MPa), 1000 °C, NNO +2, contain 4.5–6.0±0.7 wt% H2O dissolved melt equilibrium with ~30–40% phenocrysts plagioclase, two pyroxenes, Fe-Ti oxides. These sometimes evolve towards more silicic by cooling 950 °C. Rhyolitic magmas are at 200–300 MPa (i.e. ~7–11 km summit), 750 °C, ~6–8 wt% nearly aphyric (<5% biotite, oxides). Although produce fractional crystallization, history suggests either reservoirs distinct times, likely reflecting flux time fluctuations during deep recharge.