New Zealand Journal of Geology and Geophysics abstracts
The kinematics of active deformation in the North Island, New Zealand,
determined from geological strain rates
SARAH BEANLAND*
JOHN HAINES+
Institute of Geological & Nuclear Sciences
P.O. Box 30 368
Lower Hutt, New Zealand
+Present address: Bullard Laboratories, Madingley Road, Cambridge CB3 OEZ,
England.
Abstract Kinematic modelling utilising the method of Haines
& Holt extended to the case of cubic Bessel interpolation on curvilinear
grids, allows analysis of present-day horizontal motions occurring in the
Hikurangi margin, North Island, New Zealand. The velocity field solutions are
derived from first order geological data; that is, rates and orientation of
extension in the Taupo Volcanic Zone and rates and orientation of motion on the
North Island Dextral Fault Belt, against the background of the pattern of
uplift and subsidence in the margin.
A basic (preferred) velocity field is presented, with four other solutions
with different input data, to explain what controls features in the main
solution. Every one of the five solutions is the best fitting solution for the
input data in each case. All velocity fields are shown relative to the western
boundary of the model, which is considered fixed, as part of the assumed
nondeforming Australian plate.
The velocity field in the main solution includes a strong clockwise rotation
of the Hikurangi margin east of the Taupo Volcanic Zone in the north. Farther
south, shear across the North Island Dextral Fault Belt facilitates the
southwestward motion of the eastern part of the margin. An important boundary
condition for the deformation in the North Island appears to be the higher rate
of dextral shear in the Marlborough region, which accommodates the relative
motion of the Australian and Pacific plates immediately south of the Hikurangi
margin.
The extension in the Taupo Volcanic Zone, with rates onshore of
5-10 mm/yr north of where the Taupo Volcanic Zone terminates in the centre
of the North Island, and the strikeslip component of shear on the North Island
Dextral Fault Belt, of c. 20 mm/yr in the south and <5 mm/yr
in the north, account for most of the margin-parallel plate motion in the
Hikurangi margin. No other major geological strains are required to be
occurring in the North Island out of compatibility with these strains.
Keywords North Island; kinematics; fault slip rates;
extension rates; rotation; partitioning
New Zealand Journal of Geology & Geophysics, 1998, Vol. 41:
311-323
0028-8306/98/4104-0311 $7.00/0 (c) The Royal Society of New Zealand
1998
PDF file of entire paper: medium quality (3310K); (scanned from paper original: notes about this process)
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