Arc-type volcanic activity has been a major feature of the late Cenozoic geological evolution of the Pacific-Australian plate
boundary in the northern New Zealand region. The timelspace distribution patterns of arc-type rocks reflect changes in the
nature of the plate boundary as it has evolved. Inception of volcanism began in the north during earliest Miocene times (26
Ma) following ophiolite emplacement and during the next 10 Ma developed into a volcanic arc segment extending south
to the present position of the central North Island. The northern part of the arc became extinct about 15 Ma ago, but activity
continued in the central (Coromandel) part of the arc until about 5 Ma ago. In late Pliocene and Quaternary times volcanic
activity has become concentrated in a northeast trending zone which is collinear with the Tonga-Kermadec Arc.