New Zealand Journal of Geology and Geophysics abstracts
Structural collapse of a transpressive hanging-wall fault wedge,
Charwell region of the Hope Fault, South Island, New Zealand
J. Dykstra Eusden Jr*
Jarg R. Pettinga
Jocelyn K. Campbell
Department of Geological Sciences
University of Canterbury
Private Bag 4800
Christchurch, New Zealand
*Present address: Department of Geology, Bates College, Lewiston,
Maine, 04240, USA. deusden@bates.edu
Abstract The northeast-trending dextral-reverse
oblique slip Hope Fault is one of the major structures of the
Marlborough Fault System and the Australia-Pacific plate boundary zone
in the South Island of New Zealand. This study presents an analysis of
the structural and tectonic geomorphic development of the Hope Fault
Zone in the vicinity of the Charwell River to understand the
near-surface temporal and spatial structural style of deformation and
fault zone kinematics along a 10 km section of the fault.
Significant fault-related landscape units include: (1) flights of
aggradation-degradation terraces in the footwall forming an extensive
piedmont; (2) fault-dissected, sloping topography in the hanging wall
containing 95% of all the faults; and (3) eroded subhorizontal piedmont
terrace remnants that indicate the range front has repeatedly
propagated to the southeast into the footwall block. We recognise four
distinct types of fault scarps: (1) the main range-front trace of the
Hope Fault defines a releasing bend geometry, with a projected
step-over width of c. 1000 m; (2) at the foot of the range front, two
thrust faults ramp over the aggradational surfaces in the footwall
block; (3) in the toe of the hanging-wall block, c. 20 normal fault
scarps are mapped near-parallel to the main Hope Fault; and (4) more
than 100 late normal faults are oblique to the main Hope Fault and cut
obliquely across all other faults. The overall fault pattern outlines
an initial fault wedge between the thrust and early normal faults that
is 5 km in length and 1 km at its widest point. A secondary wedge
defined
by the late normal faults is 7 km in length, 2 km at its widest, and it
overprints the initial wedge. The structural/geomorphic interactions
between the initial and secondary fault wedges developed in a series of
at least four successive stages. These spatial and temporal changes in
the structural geometry and style of deformation of the Hope Fault Zone
at Charwell are interpreted to reflect the role of topographic loading
in adjusting the fault zone break-out along the range front, and is
recorded by the tectonic geomorphic landforms there.
Keywords Charwell River; Hope Fault; fault scarps;
landscape
G04001; Received 8 January 2004; accepted 26 October 2004; Online
publication date 3 June 2005
New Zealand Journal of Geology & Geophysics, 2005, Vol. 48:
295–309
0028–8306/05/4802–0295© The Royal Society of New Zealand 2005
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