STRATIGRAPHY AND CHRONOLOGY OF LATE QUATERNARY ANDESITIC TEPHRA DEPOSITS, TONGARIRO-VOLCANIC-CENTER, NEW-ZEALAND

A stratigraphy and chronology of andesitic tephras erupted from Mt Rua pehu, and other volcanoes of Tongariro Volcanic Centre, is constructed from the tephra record preserved on the southeastern Mt Ruapehu ring plain. Here, tephras of late Quaternary age (c. 22,500 years B.P. to p resent) are found interbedded with local laharic and fluvial deposits, and with distal rhyolitic tephras from Taupo and Okataina Volcanic Ce ntres. Tephras are identified from their field characteristics and str atigraphic positions relative to dated rhyolitic tephra marker beds. T he radiocarbon ages of these rhyolitic tephras provide a chronology fo r the andesitic tephras, dating back to 22,500 years B.P. All tephras erupted from Tongariro Volcanic Centre are grouped into two subgroups: the Tongariro Subgroup (redefined) and the newly defined Tukino Subgr oup. Tephras identified on the southeastern Mt Ruapehu ring plain are grouped into seven formations on the basis of lithology: Ngauruhoe For mation [dated c. 1,850 years B.P. - present], Tufa Trig Formation [dat ed c. 1,850 years B.P. - present], Mangatawai Tephra [dated c. 2,500 y ears B.P.], Papakai Formation [dated c. 9,700-2,500 years B.P.], Manga mate Tephra [dated c. 9,780-9,700 years B.P.], Pahoka Tephra [dated c. 10,000-9,800 years B.P.], and Bullet Formation [dated c. 22,500-10,00 0 years B.P.]. Tephras erupted from Mt Ruapehu are grouped into the Tu fa Trig Formation, Papakai Formation, and Bullet Formation. Papakai Fo rmation comprises both tephra and volcanic loess. The stratigraphy and chronology of the seven formations are detailed, and revisions to the earlier stratigraphy of Topping (1973, 1974) are discussed. The distr ibutions of principal tephra marker beds are shown, and tephra volumes (all < 0.2 km(3)) calculated from isopach maps wherever possible.