Residual gravity anomalies of the Taupo Volcanic Zone and adjacent region

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Stagpoole VM, Miller CA, Brakenrig T, Macdonald N, Caratori Tontini F. 2019. Residual gravity anomalies of the Taupō Volcanic Zone and adjacent region. Lower Hutt (NZ): GNS Science. 1 map + 22 p. (GNS Science geophysical map; 1).

Abstract:
The 2019 map of residual gravity anomalies of the Taupō Volcanic Zone and adjacent region is an update of the map of Stagpoole and Bibby (1999). An additional 1795 observations have been used in the 2019 compilation, bringing the total to 9189. All data used for the map have been uniformly processed and anomalies calculated using high resolution digital terrain models. The regional gravity field, used to separate the residual gravity anomalies from Bouguer anomalies, is from Stagpoole and Nicol (2008). GMT software was used for gridding the data and a 1:250,000 map was produced with the QGIS geographic information system. The 2019 map shows features in more detail than the 1999 map. Both the Taupō Volcanic Zone and the wider Central Volcanic Region are within a negative residual gravity anomaly. The whole eastern margin of the Taupō Volcanic Zone and western margin from Ruapehu to Tokoroa coincide with steep gravity gradients. North of Tokoroa, the margin of the Taupō Volcanic Zone defined from volcanism is not associated with a clearly observable gravity gradient. The negative residual gravity anomaly defining the area referred to as the Central Volcanic Region widens towards the Bay of Plenty coast in a series of steps, possibly related to older northeast-trending faults. Volcanic calderas in the Taupō Volcanic Zone identified from geological mapping correspond with prominent low-gravity features. There is also a gravity low at Mihi that is not presently defined as a caldera but may be related to caldera collapse. Low-gravity features north and northwest of Rotorua have unknown origins, although they may be partly related to thick, elevated, low-density volcanic material. Offshore, in the Bay of Plenty, a low-gravity feature corresponds with a caldera inferred from interpretation of seismic reflection data. Sedimentary basins outside the Taupō Volcanic Zone also have low residual gravity. Within the Taupō Volcanic Zone, a relative gravity high coincides with greywacke basement outcrops east of Paengaroa. Other high-gravity features may be related to near-surface greywacke basement or old andesitic volcanic centres buried beneath younger and less dense volcanic material. (auth)