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

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Abstract
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.