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 between sectors is difficult because of the scarcity of island-wide marker beds. However, eight distal calc-alkaline fall tephras (ca. 7.3 ¹⁴C ka to 64 ka) from Okataina and Taupo volcanic centres in the nearby Taupo Volcanic Zone (TVZ) have been identified on the island. These “foreign” TVZ tephras provide marker planes to correlate activity in different sectors of Mayor Island volcano, and refine an eruptive chronology. At least seventeen pyroclastic eruptions and fourteen lava-producing events (including multiple, shield-forming events) have occurred in the past ca. 64 ka. Age controls provided by the calc-alkaline tephras confirm the extremely local dispersal characteristics of many of the 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.