Potassium-argon ages for the Dunedin volcano and outlying volcanics

Abstract

Potassium-argon ages for nine rocks from the Dunedin volcano range from 13.1 ± 0.1 m.y, for Initial Eruptive Phase trachyte, to 10.1 ± 0.2 m.y. for a Third Main Eruptive Phase phonolite. The earliest of these dates defines an event in Southland (or, less probably, in earliest Taranaki) time; the full span of the activity was within the Miocene. Ages of about 15 to 16m.y. and 12.8 ± 0.2 m.y. are recorded for two representatives of the Waipiata Volcanic Formation, and serve to date the onset of major movements of the Kaikoura Orogeny in eastern Otago. The K-Ar results for rocks which have been examined paleomagnetically are compared with the polarity time scale derived from oceanic magnetic anomaly profiles.