THE GEOLOGY THE TAUPO VOLCANIC ZONE, NEW ZEALAND

The Taupo Volcanic Zone is one of the most productive magmatic systems on Earth, on a par with the Yellowstone hot spot. It is a region of rapid extension (~6-18 mm/yr), high heat flux (700 mW/m³ in some areas), and >1 km³ rhyolite eruptions every 1000 years on average. Located in the North Island, New Zealand, it is the southernmost section of the volcanic arc associated with the oblique subduction of the Pacific Plate at about ~ 45 mm/year beneath the Australian Plate at the Tonga-Kermadec-Hikurangi subduction zone. Despite the Mesozoic age of the subducting plate, the subduction interface is relatively shallow because of the present day subduction of the Hikurangi Plateau.

Calcalcaline volcanism ranges from basaltic to rhyolitic. Rhyolitic volcanism represents the 80 % of the total erupted material and is restricted to the central segment of the arc. Northeast and southwest of the central segment, andesitic volcanism dominates. Magmas are a complex mixture of crust and mantle melts.

While offshore of the Taupo Volcanic Zone a well-defined backarc basin, the Havre Trough, exists, onshore the extensional faulting coincides with the volcanic arc. The tectonic structure is known as the Taupo rift and has a very complex, high density pattern of active fault traces.

Age and geological relationships indicate that andesitic magmatism (~ 2 Ma old) preceded the development of large-scale rhyolitic systems (~1.4 Ma old) as the arc was established and evolved. Migration of volcanism shows an east- and southward trend. Large ignimbrite eruptions during relatively short periods (e.g., >1000 km³ in the period 0.34–0.32 Ma) and rapid subsidence (~ 7 – 12 mm/yr) strongly control the geomorphic and sedimentary characteristics of the Taupo Volcanic Zone. Periods of voluminous eruptions reset the landscape and provide extensive chronological markers all around New Zealand, but bury relevant information to understand the early history of the arc. These massive events are also responsible for deposition of large amounts of sediments that results in rapidly prograding coasts.