Late Cenozoic time‐lines and calc‐alkaline volcanic arcs in northern New Zealand—further discussion

In recent publications Kamp and Brothers have independently erected tectonic hypotheses concerning the Neogene subduction regime under northern New Zealand, using a foundation of time‐lines. The time‐lines are based almost solely on radiometric dates from lava flows and intrusions. They link similar dates in the eastern and western belts of calc‐alkaline volcanism, they trend northeastsouthwest, and they show a systematic younging southeastwards towards the active Taupo Volcanic Zone. The two central requirements of both authors' hypotheses are (1) that the time‐lines date the inception of arc volcanism, and (2) that volcanism did not begin at a similar time either to the northwest or the southeast of each time‐line. These two requirements are considered in detail in this paper, and it is shown, by considering the stratigraphy of the volcanic accumulations, that neither requirement is fulfilled. The Kamp‐Brothers hypothesis of a southeastwards migration of the inception of Neogene arc volcanism in the North Island lacks a factual foundation.