Long-lived shield volcanism within a monogenetic basaltic field: The conundrum of Rangitoto volcano, New Zealand

Abstract

Drilling through the edifice of Rangitoto, the youngest and largest volcano in the "monogenetic" Auckland volcanic field, reveals the multistage eruptive and magmatic history of a small basalt shield volcano. Activity commenced calendar year (cal.) 6000 cal. yr B.P., involving minor effusive and pyroclastic volcanism until 650 cal. yr B.P. This period either represents an early, less productive phase of a single polygenetic volcano, or, alternatively, Rangitoto is better described as a volcanic complex that includes one or more buried edifices concealed by the main structure. A voluminous shield-building phase occurred 650-550 cal. yr B.P., erupting isotopically uniform subalkalic basalts (M..