Chapter 5 Correlations between a heterogeneous mantle and multiple stages of crustal growth: a review of the Dun Mountain ophiolite, New Zealand

Abstract

The mantle and crustal sections of the Permian Dun Mountain ophiolite (DMO) in New Zealand's South Island have similar and potentially related tectonic histories. The mantle section records a four-part sequence of mid-ocean ridge basalt, and boninite melt extraction, followed by refertilization from supra-subduction melts and, finally, the intrusion of mafic–felsic island-arc tholeiite dykes. The crustal sequence represents a progression from mid-ocean ridge basalts to transitional island-arc tholeiites and, finally, mafic–felsic, possibly calc-alkaline, lavas; overlain by the 6 km-thick sedimentary Maitai Group. Plagiogranite zircon geochronology shows that the crustal ocean-ridge volcanism had commenced by 277.6 ± 3.3 Ma, and the youngest granites and granodiorites crystallized by 269.3 ± 4.5 Ma. All lithologies of the DMO are inferred to have formed in a broad forearc setting, representing a sequence from subduction initiation to magmatic arc formation. Sedimentary blocks within the structurally underlying ophiolitic Patuki Melange are similar to the Maitai Group, supporting a formational relationship with the DMO.