Hannah Scott
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MSc thesis: A Comparative study of the mechanisms of particle size reduction and the extent of cataclastic damage in immature and mature faults. Supervisor: Virginia Toy Email: scoha945@student.otago.ac.nz |
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Project description
The main objective of my masters is to examine the mechanisms of particle size reduction and the extent of cataclastic damage in immature and mature faults. This will be achieved by examining the microstructures within fault rocks and by examining the extent of cataclastic damage within the fault core and damage zone adjacent to a fault principal slip surface.
I intend to examine both mature and immature cataclastic fault systems. The field sites are the Alpine Fault at the Waikukupa River and Gaunt Creek, and smaller faults at Reid Stream.
Reid Stream cataclastic faults are located between Taieri Mouth and Brighton, south of Dunedin, New Zealand. They are immature faults, probably with a dilational displacement mode. The faults contain particles which range in size, shape and habit. There are clasts of schist within the fault which have been rotated with respect to the country rock. There is also a vein swarm throughout the area which may be coeval with the cataclastic faults. These veins are purely dilatational structures with no off set. We envisage that the faults are coeval and formed as the fluid within the faults drained out allowing brecciation of the wall rock into the veins.
The Alpine Fault is a large scale fault on the West Coast of New Zealand’s South Island. Displacement totals 460 km or so. The fault is a shear fault which has experienced approximately 20,000 earthquakes to get that total displacement. There is a wide zone of fault rock that has been affected by brittle processes during slip on the major structure. Within this zone there is both cataclasite and fragments of mylonite. The latter have experienced fracturing, and this may have allowed fluid infiltration which is indicated by a colour change within the rock and by veining. There is a zone of variably retrogressed mylonites which we hypothesise is related to the degree of microfracturing. There is excellent exposure of the Alpine Fault in rivers and landslips on the West Coast. So far I have focused on the Waikukupa River outcrop.