New Zealand Journal of Geology and Geophysics abstracts

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Note: Revision of some ages for the Rotoehu Ash

NEIL WHITEHEAD
ROBERT DITCHBURN

Institute of Geological and Nuclear Sciences
P.O. Box 31 312
Lower Hutt, New Zealand

Abstract  Previously published U/Th disequilibrium data for the Rotoehu Ash suggest an age of 71 +/- 6 ka, in accord with whole rock K/Ar ages (64 +/- 4 ka). However, examination of the internal ratios of isotopes in the U/Th decay series shows that the age is probably erroneous. Examination of other age data derived using various techniques gives further revised dates: 42.9 +/- 7.8 (ESR) and 35.1 +/- 2.8 (¹⁴C). The latter is now based on four, non-infinite, tightly clustered dates, but probably needs an upward calibration correction. More work is needed to resolve the continuing discrepancies. We also present eight new ²³⁰Th/²³²Th analyses for rhyolites and ignimbrites--the mean and standard deviation are 0.705 +/- 0.076.

Keywords  Rotoiti Breccia; C-14 dating; ESR dating; U/Th series dating; K/Ar dating

New Zealand Journal of Geology and Geophysics, 1994, Vol. 37: 381-383

0028-8306/94/3703-0381 $2.50/0 (c) The Royal Society of New Zealand 1994

PDF file of entire paper: medium quality (343K); (scanned from paper original: notes about this process)

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