A “least complex” dynamic model for late cenozoic volcanism in the North Island, New Zealand

Abstract

Two parallel, initially subduction‐related, volcanic belts, with contrasting activity sequences, have existed together over most of the last 22 Ma in northwestern a ad central North Island, following on naturally from Northland Allochthon emplacement. Significant lengths of the twin belts were typically active at one time. After c. 14 Ma ago, volcanism migrated “laterally” (parallel to the subduction trough) at 1–4 cm/a, as well as “frontally” (towards the trough). Marshall Belt activity, some 150–200 km west of the subduction trough, was initially andesitic, but, over at least the last 10 Ma, was additionally rhyolitic/hydrothermal, and finally basaltic. The last became “intraplate” in character (with some renewed rhyolitic and hydrothermal association), after subduction began to wane and migrate southwards. Searle Belt activity, normally 50–100 km further west from the subduction trough, and including offshore volcanism, was initially andesitic locally, then more commonly both basaltic and andesitic in close association, but without any rhyolitic or hydrothermal elements. It finally became intraplate (basaltic) as subduction waned and migrated south. An apparent geographic/time gap from Manukau to Raglan was filled by the Kiwitahi Volcanics, which were offset eastwards to half the distance from the Marshall Belt. During two short periods of time ("events"), the progression of volcanism changed markedly. The Kiwitahi Event began c. 14 Ma ago. It heralded a major southwards extension of Searle volcanism offshore, and the start of progressive southward migration of volcanism along its new, more easterly, Kiwitahi alignment. The Kaimai Event (c. 4.0–1.5 Ma ago) heralded a shift to a more western alignment in at least the Searle Belt, a change in the extension of Marshall volcanism from NNW towards Coromandel‐Northland to northeast towards Kermadec‐Tonga, and a steady southwest extension of the Hikurangi Trough. © 1994 The Royal Society of New Zealand.