Abstract:
Geochemical data for the Cretaceous to early Tertiary basaltic volcanics of northernmost New Zealand reveal there is clear chemical distinction between the basalts of the Houhora Complex and Tangihua Complex. The Tangihua Complex volcanics have both arc and backarc signatures, and a younger set of intrusions cutting the Tangihua pillow lava complexes have calc-alkaline affinities. The Houhora Complex lavas have chemical similarities with the younger Tangihua intrusives but the geochemical signature of the Houhora Complex basalts indicates generation in a well-established arc system with continental affinities. Other basic lava complexes in the Far North have compositions that differ from both the Tangihua and the Houhora Complexes. A late set of dikes, found particularly in the Three Kings Islands, can be distinguished geochemically from both the older volcanics and the younger late Miocene arc volcanism. A new model is proposed to explain the variety of chemistry and the presence of a continental signature in many of the Cretaceous lavas of northernmost New Zealand. Our model invokes, in addition, the stalled subduction and capture of the Phoenix plate and a long period of quiescence between generation and emplacement of the ophiolite.
