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1 Department of Earth Sciences, The Open University, Walton Hall, Milton Keynes MK7 6AA, UK (e-mail: s.blake{at}open.ac.uk)
2 Institute of Geological and Nuclear Sciences, Private Bag 2000, Taupo 2730, New Zealand
Scientific editing by Hugh Rollinson.
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 Taupo, varying between 0.1 and >45 km3 in minimum bulk volume, and with repose periods ranging from c. 20 to 6000 years. All magma erupted post-26.5 ka is compositionally and mineralogically distinct from pre-Oruanui and Oruanui 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 compositions: one dacitic, forming three eruptions between 20.5 ka and 17 ka, and three subtly distinct rhyolite compositions erupted in discrete periods from 11.8 to 9.95, 7.05 to 2.75 and 2.15 to 1.74 ka. Stepwise compositional variations between, and limited variation within, rhyolite groups suggest emplacement of three petrogenetically separate batches of magma within only 10 000 years. The 15–35 km3 of magma erupted at 1.77 ka evidently appeared in <103 years; this short residence time may have contributed to the lack of zonation within this magma chamber. Taupo is unusual amongst large rhyolite volcanoes in terms of the high frequency of activity since 26.5 ka, rapid stepwise changes in rhyolite compositions, and insignificant differentiation within individual subgroups. These traits are attributed to the combined effects of the extensional arc setting, thermal energy from mafic magma, and the shallow slope of the plagioclase-saturated rhyolite liquidus.
Keywords: Taupo volcanic centre, explosive volcanism, rhyolite, magmatism.
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