Subduction regression and oceanward migration of volcanism, North Island, New Zealand

In the North Island of New Zealand, calc-alkaline igneous eruptions commenced in the early Miocene and continued into the Holocene in the central Taupo and Egmont areas, but no comprehensive synthesis exists to explain either the volcanic sequence or the regional structural setting. New data, reported here, from K–Ar ages and K 2 O–SiO 2 indices for magma source depths indicate an oceanward migration pattern for volcanism, from northwest to south-east towards the Hikurangi Trench. Movement of this volcanic front throughout the Neogene and Quaternary was controlled by subduction zone regression 1 which followed rapid, shallow, non-volcanic Oligocene underplating of the island. In areas of accelerated subduction retreat, tensional tectonism caused widespread foundering of the Mesozoic greywacke basement.