Abstract
The last three eruptions at the Cordon Caulle volcanic complex, Chile, have been strikingly similar in that they have started with relatively short pre-eruptive warning and produced chemically homogeneous rhyolite to rhyodacite magma with glassy to aphyric texture. These characteristics collectively call for an understanding of the storage conditions leading to the rise and extraction of crystal-poor silicic magma from volcanoes. We have analyzed and experimentally reproduced the mineral assemblage and glass chemistry in rhyolite magma produced in the most recent eruption of Cordon Caulle, and we use these to infer magma storage and ascent conditions. Fe–Ti oxide mineral geothermometry suggests that the rhyolite was stored at ∼870–920 °C. At these temperatures, the phenocryst assemblage (plag∼An37 > cpx + opx > mag + ilm) can be reproduced under H2O-saturated conditions of between 100 and 50 MPa, corresponding to crustal depths between about 2.5 and 5.0 km. The shallow and relatively hot magma storage conditions have implications for the rapid onset, degassing efficiency, and progression from explosive to mixed pyroclastic-effusive eruption style at Cordon Caulle.
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