Structural control on volcanism and caldera development in the transtensional Taupo Volcanic Zone, New Zealand

Taupo Volcanic Zone (TVZ), New Zealand comprises several segments with different degrees of extension, and is characterised by both rhyolitic calderas and andesitic stratovolcanoes. Modern (< 300ka) TVZ, characterized by the activity of four calderas, is investigated to define: a) the overall relationship between regional structures and volcanism; b) the structural control on caldera evolution. New remote sensing and field structural data have been combined with previously published data on TVZ. The results show a general correlation between the amount of extension and the volume and style of eruption in each segment. Segments with the highest degree of extension correspond to the highly active Taupo and Okataina caldera complexes; conversely, segments with a higher degree of dextral transtension correspond to volumetrically more moderate andesitic stratovolcanoes. At a more detailed scale, the modern calderas reveal different features. 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 rift faulting within TVZ. In contrast, calderas outside the main rift (Rotorua, Reporoa) are sub-circular monogenetic collapse structures, with minor post-collapse volcanism. Their simpler evolution and structure is a function of their location away from the main zone of rifting. TVZ therefore exemplifies the situation where: 1) along the axial rift zone, magma is erupted as a function of the extension rate; 2) volcanism is manifest as different caldera structures according to their proximity to the axial zone.