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Rapid cooling and cold storage in a silicic magma reservoir recorded in individual crystals

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Science  16 Jun 2017:
Vol. 356, Issue 6343, pp. 1154-1156
DOI: 10.1126/science.aam8720

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Quick eruption after a long bake

Minerals such as zircon can record the storage conditions of magma before volcanic eruption. Rubin et al. combined traditional 238U-230Th dating with lithium concentration profiles in seven zircons from the Taupo supervolcanic complex in New Zealand to determine magma storage conditions. The zircons spent more than 90% of their lifetime in an uneruptible, mostly crystalline, and deep magmatic reservoir. The zircons were eventually transported to hotter, shallower, and eruptible magma bodies, where they spent only decades to hundreds of years before eruption. The result suggests a two-stage model for magmatic systems with large thermal variations.

Science, this issue p. 1154

Abstract

Silicic volcanic eruptions pose considerable hazards, yet the processes leading to these eruptions remain poorly known. A missing link is knowledge of the thermal history of magma feeding such eruptions, which largely controls crystallinity and therefore eruptability. We have determined the thermal history of individual zircon crystals from an eruption of the Taupo Volcanic Zone, New Zealand. Results show that although zircons resided in the magmatic system for 103 to 105 years, they experienced temperatures >650° to 750°C for only years to centuries. This implies near-solidus long-term crystal storage, punctuated by rapid heating and cooling. Reconciling these data with existing models of magma storage requires considering multiple small intrusions and multiple spatial scales, and our approach can help to quantify heat input to and output from magma reservoirs.

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