New Zealand Journal of Geology and Geophysics abstracts
Late Quaternary geometry and kinematics of faults at the southern
termination of the Taupo Volcanic Zone, New Zealand
P. Villamor
K. R. Berryman
GNS Science
P.O. Box 30 368
Lower Hutt, New Zealand.
p.villamor@gns.cri.nz
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
crosscutting 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.
Keywords rift tectonics; rift termination; normal
fault; rate of dip-slip displacement; extension; block rotation;
paleoseismology; earthquake geology; Taupo Fault Belt; Taupo Rift;
Taupo Volcanic Zone; Mt Ruapehu Graben; Ohakune-Raetihi fault set;
Karioi fault set; new structural names; NZMS 260 map sheets S20,
S21, T20, T21
G05020; Received 10 May 2005; accepted 9 September 2005; Online
publication date 28 February 2006
New Zealand Journal of Geology & Geophysics, 2006, Vol. 49:
1–21
0028–8306/06/4901–0001 © The Royal Society of New Zealand 2006
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