New Zealand Journal of Geology and Geophysics abstracts
Structure and late Cenozoic tectonics of the Southern Two Thumb Range,
mid Canterbury, New Zealand
Phædra Upton*
Dave Craw
Zoe James
Peter O. Koons*
Department of Geology
University of Otago
P.O. Box 56
Dunedin, New Zealand
*Present address: Department of Earth Sciences, University of Maine, Orono,
Maine 04469, USA.
email: phaedra.upton@maine.edu
Abstract Two crosscutting fault sets dominate the southern
Two Thumb Range-the Forest Creek Faults, and the Fox Peak Faults. The Fox
Peak Faults extend from the Fairlie Basin northward across Butler Saddle and
into Forest Creek. To the south, they consist of two north-striking, west-dipping,
reverse fault zones along the eastern flank of the Two Thumb Range. The eastern
edge of the Fairlie Basin consists of an anticlinal fold. This becomes an
east-dipping reverse fault in the north of the basin. North of Butler Saddle,
there are four Fox Peak Faults, which extend to Forest Creek where they are
cut by or end against the Forest Creek Faults. The Forest Creek Faults consist
of a set of paired reverse faults, striking northeast and dipping to the
northwest and the southeast. They can be traced from at least the Rangitata
River to Lake Tekapo and may extend even further. Late Quaternary vertical
slip rate estimates from the southern Two Thumb Range are in the order of
1-1.5 mm/yr. Geodetically derived contemporary velocities and strain rates
show a minimum in γ1 over this region. We suggest that the southern Two Thumb
Range was actively uplifting during the early middle Quaternary at rates
higher than those measured. The rates measured today reflect a slowing in
uplift rate during the late Quaternary as the loci of deformation shifted
southwest to the range front.
Keywords Southern Alps; tectonics; faults; geomorphology;
Forest Creek Faults; Fox Peak Faults
G03004; Online publication date 25 February 2004
Received 3 February 2003; accepted 24 September 2003
New Zealand Journal of Geology & Geophysics, 2004, Vol. 47: 141-153
0028-8306/04/4701-0141 © The Royal Society of New Zealand 2004
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