| Abstract: | Major- and trace-element discrimination diagrams are used in an attempt to discover the tectonic settings in which the late Cenozoic basalts and basalt-andesites of northern New Zealand evolved. The rocks of the Northland area are shown to have rift affinities, whereas those of Auckland and South Auckland appear to have evolved in an intraplate environment. It is proposed that the common link between the two groups of volcanic rocks is the Hauraki Rift. The Northland basalts are directly associated with the rift, whereas the Auckland and South Auckland rocks either developed on the flanks of the rift or their origin is linked to the evolution of membrane stresses during the opening of this rift. The basalts and basalt-andesites of the Waikato district also show an affinity with the rift, but the geochemistry is complicated by the influence of the developing Taupo Volcanic Zone which adds a shoshonitic character to these rocks. |
