New Zealand Journal of Geology and Geophysics abstracts
Structure and topographic evolution of the Main Divide in the Landsborough-Hopkins
area of the Southern Alps, New Zealand
D. Craw
Geology Department
University of Otago
P.O. Box 56
Dunedin, New Zealand
E. Nelson
Department of Geology & Geological Engineering
Colorado School of Mines
Golden, CO, USA
P. O. Koons
Department of Geological Sciences
University of Maine
Orono, ME, USA
Abstract The Landsborough-Hopkins area of the Southern
Alps lies between the tectonically active central Southern Alps and the south
Southern Alps which were most active in the Miocene. The Landsborough-Hopkins
area is underlain by interleaved tectonic slices (kilometre scale) of textural
zones 2A, 2B, and 3 schist surrounding a thin sliver of unfoliated greywacke.
Foliation and bedding are steeply dipping and northeast striking. This structural
pattern is a northern extension of Miocene deformation style which dominates
to the south. Late Cenozoic faults, particularly the Main Divide Fault Zone
of the Mt Cook area to the north, are not well developed in the Landsborough-Hopkins
area. The northeast structural grain controlled pre-Quaternary drainage orientation
of the Landsborough and Clarke Rivers, and these rivers flowed into major
river systems to the east of the topographic divide at that time. These rivers
have since been captured by the west-flowing Haast River, and the topographic
divide has stepped progressively to the east in this area. This eastward
stepping of the topographic divide was driven by tectonic shortening in the
northern part of the area. The Landsborough River capture was facilitated
by erosion at a sinistral cross-fault, the Creswicke Fault. At the capture
zone, both Landsborough River and Main Divide cut sharply across the regional
structural grain imposed by Miocene deformation. Uplift at the capture zone
has raised a c. 2 km high divide since capture. In contrast, after the Clarke
River was captured by the Haast River, the Wills River (a former Clarke tributary)
maintained the Haast Pass as a topographically low capture point. Hydrothermal
alteration and vein formation occurred in the immediate area of the Landsborough
River capture zone. Fluid flow was structurally controlled, and deposited
ankerite, quartz, and/or sulfide minerals in faults and associated fractures.
Keywords structure; Southern Alp; river capture; hydrothermal;
veins; faults; Landsborough River; Creswicke Fault Zone; new structural names
G02055; Received 14 October 2002; accepted 7 August 2003; online publication
date 13 November 2003
New Zealand Journal of Geology & Geophysics, 2003, Vol. 46: 553–562
0028–8306/03/4604–0553 $7.00/0 © The Royal Society
of New Zealand 2003
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