GEOCHEMICAL EVOLUTION THROUGH A FULL CALDERA CYCLE: TAUPO VOLCANIC ZONE, NZ

Large caldera-forming eruptions (CFEs) present a significant global hazard. While rare, they have the potential to explosively eject massive amounts of material (>1000 km³) and cause widespread catastrophic damage. Aspects of these eruptions are well-studied, yet the magma plumbing systems and crustal processes that produce such eruptions remain poorly understood, as does the spatial and temporal evolution of such systems across a full caldera cycle (including the CFEs and the smaller yet significant pre- and post-caldera eruptions between them).

The Taupo Volcanic Zone (TVZ) of New Zealand is the most active silicic volcanic system on Earth, generating large volumes of rhyolite (with lesser volumes of dacite, andesite, and basalt). Within the central TVZ, the Okataina Volcanic Center (OVC) and Taupo Volcanic Center (TVC) have both experienced CFEs within the last 50 kyr. Study of these two centers affords a unique opportunity to examine in detail the processes that generate large silicic eruptions through the full caldera cycle. We have sampled material from the two most recent CFEs in each center, Oruanui (26.5 ka, TVC) and Rotoiti (50 ka, OVC), along with eruptions that occurred before and after each. Incompatible trace element and isotope geochemistry from whole pumice and plagioclase provide constraints on mantle and crustal contributions in magma production; quartz- and plagioclase-hosted melt inclusions reveal magmatic heterogeneities often obscured on the whole-rock and mineral scale. New whole pumice lead isotope data reveal distinct signatures in the two volcanic centers suggesting either discrete magmatic sources, different contributions from crustal processes (fractional crystallization and assimilation of one or both local basement terranes), or a combination of both.