Petrology and geochemistry of intraplate basalts in the South Auckland Volcanic Field, New Zealand: Evidence for two coeval magma suites from distinct sources

Abstract

The South Auckland Volcanic Field is a Pleistocene (1.59-0.51 Ma) basaltic intraplate, monogenetic field situated south of Auckland City, North Island, New Zealand. Two groups of basalts are distinguished based on mineralogy and geochemical compositions, but no temporal or spatial patterns exist in the distribution of various lava types forming each group within the field: Group A basalts are silica-undersaturated transitional to quartz-tholeiitic basalts with relatively low total alkalis (3·0-4·6 wt %), Nb (7-29 ppm), and (La/Yb) N (3·4-7·6); Group B basalts are strongly silica-undersaturated basanites to nepheline-hawaiites with high total alkalis (3·3-7·9 wt %), Nb (32-102 ppm), and (La/Y..