Late Quaternary geometry and kinematics of faults at the southern termination of the Taupo Volcanic Zone, New Zealand

Abstract

Late Quaternary structure and kinematics at the southern termination of the Taupo Rift are investigated by means of active fault mapping and estimates of fault displacement and extension rates. Active faults in the southern Taupo Rift are normal in sense and include three major structures: the NNE‐trending Mt Ruapehu Graben; the E‐W to ESE‐WNW‐trending Ohakune‐Raetihi fault set; and the NE‐trending Karioi fault set. Displacements of young geomorphic features, fault plane exposures in roadcuts, and trenches across faults show that all faults are active contemporaneously. The Mt Ruapehu Graben is the southern extension of the modern (i.e., <26 ka) Taupo Rift (or Taupo Fault Belt, TFB), and has developed as a result of backarc extension related to the Hikurangi subduction margin. Geologic extension rate for the Mt Ruapehu Graben is estimated here at 2.3 ± 1.2 mm/yr. The other two structures strike almost perpendicular to the Taupo Rift terminating the Mt Ruapehu Graben to the south. The co‐existence of three normal fault sets in mutual cross‐cutting relations and with no significant strike‐slip on any of them may be related to local reorientation of the minimum principal stress axis (σ3) or to a stress tensor where |σ3| ≈ |σ2|. Complicated strains at the southern termination of the Taupo Rift are related to block rotations in the Hikurangi subduction margin.