North-eastward subduction followed by slab detachment to explain ophiolite obduction and Early Miocene volcanism in Northland, New Zealand

Oligocene-Miocene models for northern New Zealand, involving south-westward subduction to explain Early Miocene Northland volcanism, do not fit within the regional Southwest Pacific tectonic framework. A new model is proposed, which comprises a north-east-dipping South Loyalty basin slab that retreated south-westward in the Eocene-earliest Miocene and was continuous with the north-east-dipping subduction zone of New Caledonia. In the latest Oligocene, the trench reached the Northland passive margin, which was pulled it into the mantle by the slab, resulting in obduction of the Northland allochthon. During and after obduction, the slab detached from the unsubductable continental lithosphere, inducing widespread calc-alkaline volcanism in Northland. The new model further explains contemporaneous arc volcanism along the Northland Plateau Seamount Chain and sinking of the Northland basement, followed by uplift and extension in Northland.