New Zealand Journal of Geology and Geophysics abstracts
Growth of contractional structures during the last 10 m.y. at the southern
end of the emergent Hikurangi forearc basin, New Zealand
Andrew Nicol1
Russell Van Dissen1
Paul Vella2
Brent Alloway1
Anne Melhuish1,3
1Institute of Geological & Nuclear Sciences
P.O. Box 30 368
Lower Hutt, New Zealand
2School of Earth Sciences
Victoria University of Wellington
P.O. Box 600
Wellington, New Zealand
3Present address: Veritas DGC Ltd, P.O. Box 100, Mina Al Fahal
PC 116, Sultanàte of Oman.
Abstract Growth histories of contractional structures
at the southern end of New Zealand’s Hikurangi forearc basin have been analysed
for the last c. 10 m.y. Growth data are from outcrop and seismic-reflection
profiles that contain syntectonic strata and angular unconformities, and
from deformed fluvial terrace surfaces. Deformation is described for up to
eight intervals of time, spanning c. 12 000 yr to 5 m.y., the ages of which
were determined by biostratigraphy and tephrochronology. Reverse faults and
related asymmetric folds, which strike parallel to the subduction margin
and verge troughwards, experienced variable rates of shortening through time.
The current period of deformation commenced at c. 1.8 Ma with displacement
rates of c. 0.1-0.7 mm/yr on the main faults (i.e., Martinborough, Huangarua,
and Mangaopari Faults). Before this time there were periods of accelerated
deformation during the mid Pliocene (c. 3.4-2.4 Ma) and latest Miocene (c.
8.0-6.0 Ma). Therefore, shortening since 10 Ma accumulated mainly during
three periods of 1-2 m.y., with structures active in the Quaternary forming
in the late Miocene or earlier. Local intervals of accelerated deformation
are coincident with the timing of intervals of uplift and faulting along
much of the emergent forearc and cannot be attributed to local transfer of
displacements between faults. Instead, these intervals of deformation appear
to reflect regional changes in the kinematics of the upper plate. These changes
could arise due to margin-normal migration of strain to regions outside the
forearc basin or may indicate temporal variations in the dynamics of subduction.
Keywords subduction; reverse faults; folds; syntectonic
growth strata; angular unconformities; episodic deformation
G00066 Received 10 November 2000; accepted 13 May 2002; published 27 September
2002
New Zealand Journal of Geology & Geophysics, 2002, Vol. 45: 365-385
0028-8306/02/4503-0365 $7.00/0 © The Royal Society of New Zealand
2002
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