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

Abstract

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.