New Zealand Journal of Geology and Geophysics abstracts
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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