New Zealand Journal of Geology and Geophysics abstracts
Structure and deformational history of the inner forearc region,
Hikurangi subduction margin, New Zealand
SARAH BEANLAND*
ANNE MELHUISH
ANDREW NICOL+
JONATHAN RAVENS
Institute of Geological & Nuclear Sciences
P.O. Box 30 368
Lower Hutt, New Zealand
Abstract Seismic reflection and outcrop data from the onshore
Hikurangi forearc reveal the styles and history of deformation for a
c. 3000 km2 region between Dannevirke and Hawke's Bay. The
data cover the forearc basin, including its western and eastern boundaries, and
delineate folds and faults in a late Miocene-Recent sedimentary sequence. Five
seismic horizons, including the basement/Neogene cover unconformity (variable
age), base Waipipian (3.7 Ma), base Mangapanian (3.2 Ma), base
Nukumaruan (2.6 Ma), and base Castlecliffian (1.6 Ma) were identified
using outcrop and well ties. These horizons were traced across the study region
to provide information on the geometry, spatial distribution, and timing of
structures. To the west, the range-front fault is predominantly reverse and
separates uplifted Torlesse basement of the axial ranges from Neogene forearc
basin sediments. Structures within the forearc basin are dominated by
north-northeast-striking reverse faults and associated asymmetric folds which
parallel the subduction margin and often have sinuous traces. Faults are planar
to depths of at least 1-2 km and typically dip at 30-80deg.NW (most often
at 40-70deg.). Many faults in the basin terminate northwards and fault-normal
spacings decrease from 2-8 km in the Dannevirke area to c. 20 km
near Hastings. Angular unconformities and syntectonic strata constrain the
timing of deformation on fault/fold pairs. Faults within the forearc basin were
active over two main periods, at c. ?3.7-2.5 Ma and
c. 1.6 Ma-Recent. Active fault traces are confined to the edges of
the forearc basin. In the west, the Mohaka and Ruahine Faults have mainly
recent right-lateral offsets, but interpretation of a seismic reflection line
which crosses the Mohaka Fault indicates minimal (<300 m) right-lateral
displacement over the last 3 m.y., and lateral slip may not significantly
predate the late Quaternary. In the east, a zone of reverse faults (including
the Longlands, Poukawa, Tukituki, and Oruawharo Faults) began forming at
c. 1 Ma and remains active. Margin-normal shortening across the
forearc basin and basin-bounding structures ranges up to 5 mm/yr
(120-180 m/km) in the Dannevirke region but decreases to 1-2 mm/yr
(c. 35 m/km) near Hastings. Total shortening within the Australian
plate and normal to the central portion of the Hikurangi margin is at least
16 mm/yr (i.e. >= c. 50% of the relative plate motion component at
latitude 41deg.S), which is consistent with the plate interface being strongly
coupled over much of the last c. 0.3-0.5 m.y.
Keywords seismic reflection profiles; Dannevirke; Hawke's
Bay; Hikurangi subduction margin; forearc basin; Neogene; structural evolution;
faults; folds
New Zealand Journal of Geology & Geophysics, 1998, Vol. 41:
325-342
0028-8306/98/4104-0325 $7.00/0 (c) The Royal Society of New Zealand
1998
PDF file of entire paper: medium quality (3739K); (scanned from paper original: notes about this process)
This year's abstracts |
Journal home page |
All abstracts |
Publishing home page
