Structural control of volcanism and caldera development in the transtensional Taupo Volcanic Zone, New Zealand
The Taupo Volcanic Zone (TVZ), New Zealand, comprises several segments with variable components of extension, and is characterised by longitudinal segmentation into a central zone dominated by rhyolitic calderas and extremities with only andesitic composite volcanoes. Modern (<300 ka) TVZ was investigated to define (a) the overall relationship between regional structures and volcanism and (b) the structural control on the evolution of calderas. New remote sensing and field structural data have been combined with previously published data for TVZ. The results show a general correlation between the amount of extension and the volume and style of eruption in each segment. The segments with the greatest extension coincide with the highly active Taupo and Okataina caldera complexes; conversely, the segments with the greatest dextral transtension correspond to volumetrically less active andesitic stratovolcanoes. Within Modern TVZ, two types of caldera are distinguished based on their structure and development. Calderas within the main zone of rifting (Taupo, Okataina) are multiple (two or more major eruptions) collapse structures with rectilinear margins, overprinted by younger volcanism and faulting. Their complexity is related to the proximity (and influence) of active faulting within TVZ. In contrast, calderas peripheral to the main rift (Rotorua, Reporoa) are sub-circular monogenetic collapse structures, with minor post-collapse volcanism. Their simpler evolution and structure is a attributable to their location away from the main rift zone. Thus, TVZ exemplifies the situation where firstly, magma is erupted as a function of the extension rate along the axial rift zone, and secondly, volcanism is manifest as distinctive caldera structures according to their proximity to the axial rift zone.