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  • 21 Aug, 2019

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Omanawa Caldera
Omanawa Caldera is inferred by an area of magnetic anomaly that exists to the north-west of the Rotorua Caldera. It is also located to the north west of the present boundary of the modern Taupō Volcanic Zone but its existence would be compatible with activity in the area of intersection of Taupo Rift and Hauraki Rift before 1.9 million years ago. The area of the caldera is now mainly covered by Mamaku Ignimbrite from the Mamaku eruption of 240,000 years ago that formed the Rotorua Caldera, but there are four earlier major ignimbrite eruptions of the Taupō Volcanic Zone that would have also contributed to its infilling.

Possible Eruptions

Eruptions from the Omanawa Caldera would explain formations such as the Waiteariki ignimbrite which covers much of the Bay of Plenty and forms the bulk of the Whakamarama Plateau. If this eruption came from the caldera, it would date the major caldera formation to 2.1 million years ago. This large single eruption event had a DRE of 870 ± 87 km (209 ± 21 cu mi). However, there are at least eight large eruptions that occurred in the Tauranga Volcanic Centre between 2.4 and 1.9 million years ago and at this time which ones relate to this caldera can not be definite. If any involved the caldera, as they had smaller eruptive volumes than the Waiteariki eruption the caldera structures that resulted from each of these eruptions would be smaller and might be spread out in area. To date there is no other obvious closer inferred volcanic structure to assign a super volcanic eruption to, so at least some of these eruptions are likely to be associated with the Omanawa Caldera magnetic anomaly.

Possible tectonic relationships

The Omanawa Caldera magnetic anomaly may be part of the transition structures of the Tauranga Volcanic Centre to the old Taupō Volcanic Zone and is sometimes mapped as the eastern most manifestation of the later. In this model the Omanawa Caldera can represent the first silicic system of the Taupō Volcanic Zone, rather than the last of the Tauranga Volcanic Centre. The Mangakino caldera complex which started forming 1,620,000 years ago, to the southwest, is part of the old Taupō Volcanic Zone and more recent than the postulated Omanawa Caldera so fits with modelling of Taupō Rift extension to the south west towards Hauhungatahi in the period 2,100,000 to 900,000 years ago.

In the Tauranga Volcanic Centre area a strongly negative Bouguer gravity anomaly exists between Katikati and Matakana Island in Tauranga Harbour which could also be a buried caldera structure related to Tauranga Volcanic Centre activity. There is no definite rhyolite dome relationship here and the geological structures observed to date in the southern Kaimai Ranges do not suggest a caldera underlies the southern Kaimai's, which have been suggested as another Tauranga Volcanic Centre caldera.

References

  1. ^ Pittari, Adrian; Prentice, Marlena L.; McLeod, Oliver E.; Zadeh, Elham Yousef; Kamp, Peter J. J.; Danišík, Martin; Vincent, Kirsty A. (2021). "Inception of the modern North Island (New Zealand) volcanic setting: spatio-temporal patterns of volcanism between 3.0 and 0.9 Ma" (PDF). New Zealand Journal of Geology and Geophysics. 64 (2–3): 250–272. doi:10.1080/00288306.2021.1915343. S2CID 235736318.
  2. ^ Stagpoole, V; Miller, C; Caratori, Tontini F; Brakenrig, T; Macdonald, N (2021). "A two million-year history of rifting and caldera volcanism imprinted in new gravity anomaly compilation of the Taupō Volcanic Zone, New Zealand". New Zealand Journal of Geology and Geophysics. 64 (2–3): 358–371. doi:10.1080/00288306.2020.1848882. S2CID 230527523.
  3. ^ Prentice, Marlena Lee (2023). Silicic volcanism of the Tauranga Volcanic Centre and the climactic Waiteariki supereruption at the dawn of the Taupō Volcanic Zone; PhD dissertation (PDF) (Thesis). The University of Waikato. Retrieved 10 September 2023.
  4. ^ Prentice, Marlena; Pittari, A.; Kamp, P; Lowe, David J. (2020). "The 2.1 Ma Waiteariki Ignimbrite: Defining a new super-eruption at the onset of TVZ volcanism". Geoscience NZ 2020.
  5. ^ Prentice, Marlena; Pittari, Adrian; Lowe, David J.; Kilgour, Geoff; Kamp, Peter J.J.; Namaliu, Miriam (2022). "Linking proximal ignimbrites and coeval distal tephra deposits to establish a record of voluminous Early Quaternary (2.4–1.9 Ma) volcanism of the Tauranga Volcanic Centre, New Zealand". Journal of Volcanology and Geothermal Research. 429 (107595): 107595. doi:10.1016/j.jvolgeores.2022.107595. ISSN 0377-0273. S2CID 249264293.
  6. ^ Cooper, George F; Wilson, Colin; Millet, Marc-Alban; Baker, Joel (2016). "Generation and Rejuvenation of a Supervolcanic Magmatic System: a Case Study from Mangakino Volcanic Centre, New Zealand". Journal of Petrology. 57 (6): 1135–1170. doi:10.1093/petrology/egw035.
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