TAUPO VOLCANIC ZONE CALC-ALKALINE TEPHRAS ON THE PERALKALINE MAYOR-ISLAND VOLCANO, NEW-ZEALAND - IDENTIFICATION AND USES AS MARKER HORIZONS

Mayor Island is a peralkaline rhyolitic caldera volcano characterised by numerous, sector-confined pyroclastic deposits, together with lavas forming at least five composite shields. Correlation of sequences bet ween sectors is difficult because of the scarcity of island-wide marke r beds, However, eight distal calc-alkaline fall tephras (ca. 7.3 C-14 ka to 64 ka) from Okataina and Taupo volcanic centres in the nearby T aupo Volcanic Zone (TVZ) have been identified on the island. These ''f oreign'' TVZ tephras provide marker planes to correlate activity in di fferent sectors of Mayor Island volcano, and refine an eruptive chrono logy. At least seventeen pyroclastic eruptions and fourteen lava-produ cing events (including multiple, shield-forming events) have occurred in the past ca. 64 ka. Age controls provided by the calc-alkaline teph ras confirm the extremely local dispersal characteristics of many of t he Mayor Island eruptives and show that K/Ar ages as young as 25-33 ka on obsidians with 4.2-4.4% K2O are reliable.