New Zealand Journal of Geology and Geophysics abstracts

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Kawerau Ignimbrite: a 0.24 Ma ignimbrite erupted from the Okataina caldera complex, Taupo Volcanic Zone, New Zealand

S. W. BERESFORD
J. W. COLE

Department of Geological Sciences
University of Canterbury
Private Bag 4800
Christchurch, New Zealand

Abstract  "Sandy black" ignimbrites within the Taupo Volcanic Zone, New Zealand, are often incorrectly correlated. One of these ignimbrites was considered to be the lateral equivalent of the Kaingaroa Ignimbrite, but an integrated study of field geology, lithic componentry, mineralogy, and geochemistry of juvenile pumices has shown the ignimbrite is a separate unit, here termed the Kawerau Ignimbrite, with a source in the southern part of the Okataina caldera complex. The ignimbrite comprises two subunits that locally grade into each other: a lower partially welded "sandy black" ignimbrite and an upper tan-buff pumice-poor ignimbrite. Mineralogy and whole-rock pumice geochemistry indicate significant compositional variation with two magma types: a high-silica rhyolite (type A) and a dacite (type B). Both magma types show anomalously high Zr, Zn, and Hf, with type-B pumice having similar values to weakly peralkaline rhyolites. The study highlights the importance of integrating all study methods before correlating units of apparent similar lithology.

Keywords  Kawerau Ignimbrite; Kaingaroa Ignimbrite; manganoan fayalite; correlation; Taupo Volcanic Zone; new stratigraphic name

New Zealand Journal of Geology & Geophysics, 2000, Vol. 43: 109-115

0028-8306/00/4301-0109 $7.00/0 (c) The Royal Society of New Zealand 2000

PDF file of entire paper: medium quality (1796K); (scanned from paper original: notes about this process)

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