User:Ddaveonz/sandbox/Draft Taupo Volcanic Zone

The Taupo Volcanic Zone (TVZ) is a volcanic area in the North Island of New Zealand that has been active for the past two million years and is still highly active. Mount Ruapehu marks its south-western end and the zone runs north-eastward through the Taupo and Rotorua areas and offshore into the Bay of Plenty. It is part of the larger Central Volcanic Region that extends further westward through the western Bay of Plenty to the eastern side of the Coromandel Peninsula and has been active for four million years. The Taupo Volcanic Zone is widening east–west at the rate of about 8 mm per year. It is named after Lake Taupo, the flooded caldera of the largest volcano in the zone, the Taupo Volcano.

Sources

Geography

Location, town and cities, geothermal areas

The Taupo Volcanic Zone is approximately 300 km long in a NNE–SSW direction, of which 200 km is on land, and 60 km wide.

The central region of the present-day TVZ has an average heat flow of 700 mW/m² and a total flux of 400 GW.

Geology

[This section is the introduction to geological characteristics of the TVZ:

• Types of eruptions: andesitic, basaltic, dacitic, ryholitic (Wilson 1995)
• Division into Southern, Central, Northern zones characterised by type of volcanic activity. The central zone is unusual amongst arc-related volcanic systems in the unusually high proportion of rhyolite erupted (Wilson 1995)
• The calderas of the central zone (Wilson 1995)
• Geothermal activity
• Tectonic aspect: locations of significant faulting

The Taupo Volcanic Zone forms the southernmost section of the Tonga-Kermadec volcanic arc, where it intersects with the continental crust of Zealandia and terminates in the central North Island. The TVZ is globally recognized for the intensity and frequency of volcanic and geothermal activity, which puts it in the same class as the Yellowstone volcanic system. The Taupo and Okataina volcanoes are the two most frequently active and most productive rhyolitic volcanoes on Earth. The TVZ has been created by the westward subduction of the Pacific plate under the Australian Plate under the North Island.

Geologic Setting and Processes

• Convergence of plates
• Return flow zone and southwestern edge of magmatism
• Hikurangi plateau
• Tectonic aspect: extension and rifting of the crust
• How these processes may drive the unusually high levels of rhyolitic activity
• Why only andesitic activity in the southern zone? (Reyner 2006)

The Taupo Volcanic Zone is the most recent phase in a complex history of interactions between the Australian and Pacific plates over the past 25–30 million years. For the last 16 million years, the Pacific plate has been subducting under the Australian plate in a west-southwestward direction. Initially, the Colville Arc was the volcanic arc associated with this subduction, however, slab roll-back and back-arc basin opening which began approximately 6 million years ago has led to the formation of the Tonga-Kermadec Arc, which is the currently active volcanic arc.

The Pacific plate converges with the Australian plate at an angle, and so it drags the forearc region of the Australian plate to the southwest with it as it subducts, which results in the clockwise rotation of the eastern part of the North Island. This in turn is accommodated by back-arc extension in the Taupo Volcanic Zone and crustal compression in the Whanganui Basin to the southwest. (Significance of this extension as it relates to the TVZ) As the Pacific plate descends into the mantle, it drags part of the overlying mantle wedge down with it. A corresponding return flow of hotter material rises within the mantle wedge, and the Taupo Volcanic Zone is located where this upwelling material meets the bottom of the Australian plate.

Theories about what drives it (Wilson 2016, Reyners 2006): extent of Hikurangi Plateau, upwelling under the central zone, lateral flow from the southwest providing additional flux (Reyner 2006 p.580), etc. Significant volume of partial melt just west of Taupo caldera (Wilson 2016, Reyners 2006)

Evolution

• The three phases
• Tectonic aspect: how rifting may have changed over time (propagation to the southwest, etc.)
• Significant volcanic events
• Theories of propagation of the TVZ to the southwest (Reyner 2006 pp.580-581)

The earliest volcanic activity in the Taupo Volcanic Zone began approximately 2 million years ago. Activity at this time was andesitic, but from 1.6 million years ago, rhyolitic activity began and quickly became the dominant form of volcanic activity.

The evolution of the TVZ is conventionally divided into three stages: the "Old TVZ" which represents all activity that occurred earlier than the Whakamaru eruptions, i.e. activity that occurred between 2 million years ago and 340,000 years ago; the "Young TVZ" which represents all activity that occurred between the Whakamaru eruptions 340,000 years ago and the Rotoiti eruption 61,000 years ago; and the "Modern TVZ" which includes all activity that has occurred since the Rotoiti eruption, i.e. all activity in the last 61,000 years.

Key events in the development of the TVZ: key eruptions: Whakamaru, Rotoiti, Oruanui; formation of each caldera and caldera collapse events

Relationship between rifting and volcanic events?

Limitations of data and ongoing questions