Trends in rhyolite geochemistry, mineralogy, and magma storage during the last 50 kyr at Okataina and Taupo volcanic centres, Taupo Volcanic Zone, New Zealand

Equilibrium between glass and phenocrysts in OVC and TVC rhyolites suggests that crystallisation occurs shortly prior to eruption. Low crystal contents (∼5-15%), and the lack of pre-eruptive gradients suggests rapid convection and/or short crustal residence times. Melts are extracted from greater depths, as indicated by high whole-rock temperatures, before ponding in shallow storage chambers. The distinct pressure, temperature, and oxygen fugacity of each magma erupted, and the lack of temporal (fractionation) trends, suggests that the magmas are not derived from a single common magmatic system at their respective centres. OVC magmas are more oxidised than those from TVC, at any given temperature, suggesting the source areas are fundamentally different. Volumetrically subordinate pumice clasts in some OVC ejecta display mingled glasses and disequilibrium crystal populations resulting from the intrusion and mingling of separate rhyolite magmas prior to eruption. At OVC, some crystal-rich stagnating magmas have become reactivated by new intrusions or engulfed into larger magma bodies, and some eruption episodes were primed and triggered by mafic intrusion.