Are the volcanoes at Banks Peninsula shield or stratovolcanoes?

Answer 1

Banks Peninsula is a complex of extinct shield volcanoes resulting from intraplate or "hotspot" volcanism 8-11 million years ago, built mainly from alkali-basalt lavas. In some shield volcano eruptions, basaltic lava pours out of a long fissure instead of a central vent. This appears to have occured in the case of the craters that eventually eroded to form the Lyttleton and Akaroa Harbours. The Lyttleton volcano formed first (11-10 million years ago) and the Akaroa volcano later (9-8 million years ago). The Banks Peninsula complex formed at the margin of the area affected by compressional tectonics on the Pacific/Australian Plate boundary. Eruptions on the Peninsula continued until about 6 million years ago, which coincides roughly with the epoch at which compressional tectonics became established in the Canterbury and Otago regions. Geologists therefore speculate that the onset of compressional tectonics (of the sort dramatically witnessed in Canterbury in 2010/2011) turned off the alkaline intraplate volcanism of southern New Zealand; i.e., it is the reason that these volcanos have been extinct for millions of years.

[Source: "Intraplate volcanism in eastern Australia and New Zealand" By R. Wally Johnson, Jan Knutson, Stuart Ross Taylor, Australian Academy of Science (Cambridge University Press, 1989)]