Timing and conditions of formation of granitoid clasts erupted in recent pyroclastic deposits from Tarawera Volcano (New Zealand)

摘要: Abstract Granitoid clasts in pyroclastic deposits of the 0.7 ka (Kaharoa) eruption from intra-caldera Tarawera volcano Okataina Volcanic Centre (OVC), New Zealand, provide an insight to plutonic processes beneath one most productive Quaternary rhyolite centers on Earth. SIMS U–Th data for 79 granitoid zircon crystals six reveal a unimodal age spectrum yielding weighted average model 208 ± 4 ka (MSWD = 1.2; n = 72). The remaining are at secular equilibrium and U–Pb analyses indicate that few these outliers date back ~ 750 ka, period significantly longer than known volcanic record OVC (probably ~ 550 ka). In contrast, crystallization co-erupted pumice lava Kaharoa event, three preceding eruptions, occurred mostly during 0–50 ka, reflecting separate magmatic history. Brittle deformation features, incipient alteration, low-δ18O whole-rock compositions (+ 3‰) consistent with shallow solid intrusion has interacted meteoric hydrothermal fluids. However, δ18O zircons (+ 5.4 ± 0.2‰; n = 11) compositions, thus interaction post-emplacement. granitoids contrast those ejected ~ 40–60 ka caldera-forming Rotoiti event were partly molten display spectra indistinguishable pumices, suggesting latter derived contemporaneous crystal mush. case shows zones system remained despite frequent voluminous magma production included events. Such long-lived sub-solidus systems would act as barriers melt connectivity country rock, but also potential source antecrysts/xenocrysts subsequent eruptions. This exemplifies how evolution can diverge even close proximity.