Priming and eruption of andesite magmas at Taranaki volcano recorded in plagioclase phenocrysts

Abstract Plagioclase phenocrysts in pre-historic andesites provide insight to the dynamics of magma formation and eruption at Taranaki volcano, New Zealand. The phenocryst population has a diversity relic cores total situ 87 Sr/ 86 Sr range 0.70440–0.70486. Within-sample variations 0.00018 0.00043 indicate that many are antecrysts and/or xenocrysts, derived from multiple crystal mush bodies. Sr-isotopic differences consecutive eruptions different magmas were tapped or formed on centennial timescale. Most have resorption/calcic regrowth zone(s) with elevated FeO* but invariant MgO zonation profiles. They likely record mafic melt inputs, subsequent storage temperature caused re-equilibration Mg gradient. However, distinct rim types final pre/syn-eruptive magmatic conditions. Those erupted 1030–1157 CE, 1290–1399 CE 1780–1800 characterised by resorption calcic sharp gradients. entry into system few days less before based diffusion chronometry. In contrast, most 1755 1655 pre-1 ka events, texturally uniform rims, compositionally consistent closed-system crystallisation. This suggests alternating external internal triggers. Alternatively, rate reactivation via intrusion may dictate whether there was sufficient time for mineralogical response be recorded part all system. With respect anticipating future eruptions, plagioclase suggest multi-stage priming rapid onset trigger.