A two million-year history of rifting and caldera volcanism imprinted in new gravity anomaly compilation of the Taupō Volcanic Zone, New Zealand

ABSTRACT

The Taupō Volcanic Zone (TVZ) is characterised by a negative residual gravity anomaly that correlates with a zone of normal faulting, subsidence and voluminous silicic volcanism from c. 2 Ma. A steep gravity gradient is associated with downfaulting of the Mesozoic metasedimentary basement at its eastern and western margins, and all known calderas are associated with prominent local gravity lows. New Bouguer and residual gravity anomaly maps are presented that show improved detail over previous maps. The western margin of the TVZ shows as a series of parallel northeast-trending boundaries and northwest-trending step-over zones. The new map also reveals the complex boundaries of the Okataina caldera, and greater detail north of Taupō where gravity lows at Reporoa and Mihi form part of a larger and more extensive, elliptical low-gravity feature, suggesting that they may be separate collapse areas within a larger caldera complex. Around the margins of the TVZ, the Hauraki graben/rift and sedimentary basins at Hamilton, Waimiha, Galatea and Waiohau are also characterised by low residual gravity.

KEYWORDS:

• Taupō Volcanic Zone
• Taupō Rift
• Hauraki graben
• Bouguer gravity
• residual gravity
• gravity anomaly
• caldera
• volcanism
• normal fault

Acknowledgements

The authors thank the many landowners, iwi, and the Department of Conservation for access to their lands to undertake gravity measurements over the last decades. Helpful discussions were provided by Graham Leonard and Wanda Stratford. We thank Simon Barker and an anonymous referee for helpful comments as well as editorial handling by Gabor Kereszturi.

Disclosure statement

No potential conflict of interest was reported by the author(s).

Data availability statement

The gravity data used in this paper are available from the GNS Science Land Gravity Database (https://doi.org/10.21420/DRDW-VC72) or can be accessed from university theses and University of Auckland Geothermal Workshop papers. A report giving the sources of the gravity data and enclosing copies of the residual gravity anomaly grid (in geotif and kmz format) is freely available from GNS Science online shop (https://shop.gns.cri.nz/gnsgpm_01-pdf/).

Additional information

Funding

This project was funded by the Ministry of Business, Innovation and Employment through the GNS Science Te Riu-a-Māui / Zealandia SIFF research programme.