The Taupo Volcanic Zone (TVZ) is the largest active volcanic belt in New Zealand._x000D_
It is <0.6 m yr old and represents the youngest part of the central volcanic region._x000d_>
Two parts of TVZ can be distinguished: an eastern andesitic arc, extending from White Island to Tongariro Volcanic Centre and comprising tholeiitic basalt/andesite/dacite volcanoes, and a western ensialic marginal basin filled with 2-3 km of predominantly rhyolitic pyroclastics and lavas. Volcanism in the marginal basin has been dominated by large ignimbrite eruptions accompanied by caldera collapse. After collapse rhyolite domes were extruded and numerous airfall tephras erupted from each centre. Faulting within the marginal basin occurs in en echelon belts and in places high-alumina basalts have been erupted along fissures associated with the faults. The basin is both widening and subsiding, and is crossed by lineations which may be surface expressions of dextral faults in the basement._x000D_
A combination of extension and dextral shearing would provide favourable sites for ignimbrite eruptions. The crust under TVZ is thin (ca. 15.5 km) and seismic velocities increase progres- sively with depth. The underlying mantle has sn anomalously low velocity (7.4 km/s) suggesting it is partially molten.