New Zealand Journal of Geology and Geophysics abstracts
Recognition of active reverse faults and folds in North Canterbury, New
Zealand, using structural mapping and geomorphic analysis
Nicola J. Litchfield1
Jocelyn K. Campbell2
Andrew Nicol1
1Institute of Geological & Nuclear Sciences
P.O. Box 30 368
Lower Hutt, New Zealand
2Department of Geological Sciences
University of Canterbury
Private Bag 4800
Christchurch, New Zealand
Abstract In areas of limited geological exposure and
discontinuous marker beds, many faults or parts of faults are difficult to
detect and their displacement and strike length, for example, hard to quantify.
Here, we use structure contouring of a partly exhumed basement unconformity
surface together with stream gradient and sinuosity indices to help resolve
moderate sized faults (<100 m throws) and folds that were either not detected
or only poorly delineated by either structural or geomorphic mapping. Data
are from active reverse faults and associated folds in North Canterbury,
at the outer edge of the Australia-Pacific plate boundary collision zone
in New Zealand. Structural mapping defines three major, parallel, ENE-striking
reverse fault systems, with associated folds and vertical displacements of
100–950 m. In addition to showing greater trace lengths and connectivity
of the main faults, structure contours and stream analyses highlight six
faults with throws of <100 m, which were previously unrecognised. These
faults accounted for <15% of the total vertical displacement across the
region of study. Conventional mapping, therefore, permits the identification
of the principal faults, while geomorphic analysis provides a more complete
understanding of the locations and displacements of faults in the system.
In addition, geomorphic analysis provides a means of identifying low slip-rate
structures (e.g., <0.2 mm/yr) which have experienced Quaternary activity.
Keywords reverse fault; fault-related fold; exhumed
unconformity surface; stream gradient index; stream sinuosity index; fault-throw
resolution; active tectonics; North Canterbury; Moores Hill Fault; Moores
Hill Anticline; Moores Hill Syncline; Tipapa Syncline; Mt Alexander Fault;
Mt Alexander Anticline; Mt Alexander Syncline; Scargill Hills Outlier; Maxwelton
Fault; Foxdown Anticline; Foxdown Syncline; Scargill Creek Fault; Scargill
Anticline; Hurunui Bluff Fault; Hurunui Bluff Anticline; Trig C Fault; new
structural names
G02034; Received 1 July 2002; accepted 11 June 2003; online publication
date 13 November 2003
New Zealand Journal of Geology & Geophysics, 2003, Vol. 46: 563–579
0028–8306/03/4604–0563 $7.00/0 © The Royal Society of New Zealand
2003
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