Abstract

Many arc silicic igneous provinces exhibit compositional variability defined by oscillation between dry and wet rhyolites. The origins of this variability are often uncertain due to the poor constraints on the compositions of the mantle-derived inputs to the lower crustal hybridization zones. The Taupo Volcanic Zone (TVZ) in New Zealand, the most productive of modern silicic igneous provinces, exhibits variability of rhyolite compositions, but small-volume coeval basaltic eruptions also occur, making it an ideal location to study the mantle contributions to these distinctive types of rhyolite. Here we present major and trace element data from 12 magmatic centers that reveal that mafic units from the northern portion of the central TVZ are enriched in large-ion lithophile elements (LILE) in comparison to the southern TVZ. The results of models quantifying slab-derived contributions to the mantle suggest that the observed heterogeneity in LILE concentrations, and volatile fugacities, can be explained by variable amounts of subduction-derived fluid within the melting region of the basalts. These new data and modeling results provide the first direct evidence that the spatial diversity in the flux of mantle-derived basalts and associated volatile elements into the lower crustal differentiation system of the TVZ are coincident with wet to dry rhyolite compositional variability.

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