ZIRCON FISSION-TRACK AGE FOR MIDDLE PLEISTOCENE RANGITAWA TEPHRA, NEW-ZEALAND - STRATIGRAPHIC AND PALEOCLIMATIC SIGNIFICANCE

Rangitawa Tephra is an important stratigraphic marker in mid-Pleistocene marine and terrestrial sequences in New Zealand and adjacent ocean basins. Zircon fission track ages (ZFTA) on Rangitawa Tephra from five sites in the southern North Island yield mean site ages in the range 0.34 to 0.40 Ma with a weighted mean of 0.35 +/- 0.04 Ma (1-sigma). On the basis of glass shard major-element chemistry, ferromagnesian mineralogy, ZFTA and similarity of paleomagnetic dates of proposed tephra correlatives in deep-sea cores, it is concluded that Rangitawa Tephra represents a major eruptive event in the Taupo Volcanic Zone most probably associated with eruption of the Whakamaru-group ignimbrites (0.35-0.39 Ma) or less likely the Paeroa Range Group Ignimbrites (0.36-0.38 Ma). Pollen analyses from two onshore sites, together with regional loess stratigraphy, show that Rangitawa Tephra was erupted during a glacial period. The ZFTA and previously reported oxygen isotope data from DSDP Site 594 indicate that Rangitawa Tephra was erupted near the end of oxygen isotope stage 10.