Arc-type
volcanic activity has been a major feature of the late Cenozoic geological
evolution of the Pacific-Australian plate boundary in the northernNew Zealand
region. The time/space 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 15Ma 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.

These time/space patterns can be interpreted in two
ways. Firstly, if relative plate motion was essentially transform in the region
prior to 26 Ma then a small change in the relative plate vectors may have
initiated subduction and the associated volcanism. Southward evolution of the
arc can then be seen as the straightening and extension of a single arc.
Alternatively, the distribution of volcanic rocks can be interpreted as the
capture of a relatively short lived arc by southward migration of the dominant
Tonga-Kermadec subduction system.