Cretaceous‐oligocene multiphase magmatism on three kings islands, northern New Zealand

Abstract

The Three Kings Islands, New Zealand, contain some of the few on‐land autochthonous examples of Cretaceous‐Oligocene magmatism in the Southwest Pacific region. Analyses of primarily mafic lavas reveal two different geochemical signatures, both predominantly medium‐K series lavas with Mg# <40 and characteristically flat, high field strength element and high large‐ion lithophile element contents normalised against mid ocean ridge basalts (MORB). Group 1 lavas have continental arc signatures and were generated by partial melting of an N(normal)‐MORB source indicating formation during the final stages of arc volcanism as crustal thinning began, during spreading along the eastern Gondwana margin. The younger Group 2 lavas were generated from an enriched mantle source with high degrees of partial melting and have minor continental signatures; we propose they represent Oligocene arc volcanism. These results support the hypothesis that between the mid cretaceous and early Tertiary, the New Zealand sector of eastern Gondwanaland underwent long periods of compressional tectonics resulting in subduction‐related volcanism and associated magmatism.