Correlation of Papanetu Tephra to Karapiti Tephra, central North Island, New Zealand

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Abstract
New road exposures around Lake Rotoaira and south and east of Lake Taupo have provided the opportunity to re-examine the stratigraphic relationships between the rhyolitic Papanetu and Karapiti Tephras (c. 10 000 years B.P.). Papanetu Tephra is everywhere typical of a distal rhyolitic tephra; it is thin (< 2 cm), fine grained, and forms discontinuous lenses. The source of Papanetu Tephra was previously inferred to be Kuharua dome, southeast of Turangi. A re-examination of the coverbeds on Kuharua has identified Rotoaira Lapilli (13 800 years B.P.) overlying 15–20 000 year old eolian deposits that, in the surrounding region, are themselves overlain by Papanetu Tephra. Thus it is doubtful that Kuharua is the source. Stratigraphic correlation, supported by mineralogy, glass and mineral chemistry, and chronology, here establishes Papanetu Tephra as the distal equivalent of Karapiti Tephra. Microprobe analyses reveal that previous chemical distinction between these two tephras was probably caused by sample contamination by andesitic tephra. A new isopach map for Karapiti Tephra is presented from which a total volume of c 1.5 km3 of tephra is calculated. Tephra distribution is bilobed. Isopachs show a bulge to the south thinning more rapidly than in other directions. This bulge is created by an obsidian-rich fine ash upper unit that probably was erupted during the formation of a rhyolite dome at Acacia Bay, and was dispersed by a northerly wind. As Papanetu Tephra is no longer a separate, viable stratigraphic unit, we recommend that this name should lapse.

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