Late Quaternary evolution of a hyperactive rhyolite magmatic system: Taupovolcanic centre, New Zealand

Taupo volcanic centre has been active for c. 300 000 years. Since the c. 26 .5 ka caldera-forming Oruanui eruption 28 eruptions have occurred from Taup o, varying between 0.1 and >45 km(3) in minimum bulk volume, and with repos e periods ranging from c. 20 to 6000 years. All magma erupted post-26.5 ka is compositionally and mineralogically distinct from pre-Oruanui and Oruanu i eruptives, and is inferred to have formed at or after 26.5 ka. Four post- Oruanui magma types are identified on the basis of whole rock and mineral c ompositions: one dacitic, forming three eruptions between 20.5 ka and 17 ka , and three subtly distinct rhyolite compositions erupted in discrete perio ds from 11.8 to 9.95, 7.05 to 2.75 and 2.15 to 1.74 ka. Stepwise compositio nal variations between, and limited variation within, rhyolite groups sugge st emplacement of three petrogenetically separate batches of magma within o nly 10 000 years. The 15-35 km(3) of magma erupted at 1.77 ka evidently app eared in <10(3) years; this short residence time may have contributed to th e lack of zonation within this magma chamber. Taupo is unusual amongst larg e rhyolite volcanoes in terms of the high frequency of activity since 26.5 ka, rapid stepwise changes in rhyolite compositions, and insignificant diff erentiation within individual subgroups. These traits are attributed to the combined effects of the extensional are setting, thermal energy from mafic magma, and the shallow slope of the plagioclase-saturated rhyolite liquidu s.