Organization and thermal maturation of long-lived arc systems: Evidence from zircons at the Aucanquilcha volcanic cluster, northern Chile

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.