Abstract

Age and trace element data from zircons constrain the progressive stages of development of the magmatic underpinnings of the long-lived, dacite-dominant Aucanquilcha volcanic cluster in northern Chile. Large U/Pb age spectra (<2 m.y.) are observed in the samples from the beginning and waning stages of the volcanoes, which are at times characterized by low eruption rates. In contrast, small age spectra (<500 k.y.) are typical of samples from the middle stage of the cluster, a time characterized by high eruptive output. The preservation of precursor crystals is interpreted to reflect the thermal maturity of the magmatic system; the middle stage is a time of homogenization and increased volumetric output rate and corresponds to a time of substantial resetting of the zircon ages, presumably through pervasive dissolution and crystallization. Crystallization temperatures for Aucanquilcha volcanic cluster zircons, calculated using the Ti-in-zircon thermometer, range from 690 to 920 °C, with typically ∼100 °C variation in single samples. Higher concentrations of Ti, and thus hotter zircon crystallization temperatures, are recorded in samples that correspond to the eruptive flare-up. The timings of plutonic and volcanic events correspond, based on correlation of peaks in zircon spot ages with eruptive episodes.

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