The compositional diversity and temporal evolution of an active andesitic arc stratovolcano: Tongariro, Taupō Volcanic Zone, New Zealand

Abstract New geochemical data, including Sr–Nd–Pb isotopes for whole-rock and groundmass samples, are reported edifice-forming eruptives at Tongariro volcano, Zealand, which span its ~ 350 ka to late Holocene history. medium-K basaltic-andesites dacites (53.0–66.2 wt% SiO 2 ) that evolved via assimilation-fractional crystallisation (AFC) processes partly or mostly in the uppermost 15 km of crust. When ordered chronologically using a high-resolution 40 Ar/ 39 Ar-dated eruptive stratigraphy, compositional data show systematic 10–130 kyr cycles. Mafic replenishment events inferred from MgO values occurred 230, 151, 88 56 Holocene, with high-MgO flank vents erupting 160, 117, 35 17.5 ka. Cycles Sm/Nd, 87 Sr/ 86 Sr, 143 Nd/ 144 Nd Pb isotopic ratios, decoupled MgO, K O Rb/Sr cycles, indicate periods prolonged crustal residence magmas 230 100 95 30 AFC modelling shows intermediate silicic melt compositions, r-values between 0.1 1, needed reproduce arrays. models also 20% average magma comprises assimilated (meta)sedimentary basement material. Locally, adjacent Ruapehu volcanoes attain their most crust-like Sr compositions ka, paralleling zircon model-age modes rhyolitic Taupō volcano 50 NNE. These coincidences suggest timing tempo assembly all three were contemporaneous may have been tectonically influenced since least 200