The Mackenzie Basin

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Understanding our dynamic landscape gives us great insight into the past and the ability to make educated predictions of possible future events of the world we live in today. The Mackenzie basin is a wide valley basin containing three glacial lakes which have the potential to provide understanding into the glacial, tectonic and climate history of the Southern hemisphere and in particular, New Zealand. The South Island of New Zealand is characterised by oblique continental collision of the Australian and Pacific tectonic plates, forming the dominant Southern Alps. The plate boundary is known as the Alpine fault and attention has often be associated with motion on the western side of the Alps, but more recently studies have been focussing on the eastern side. Upton1 writes in the New Zealand Journal of Geology and Geophysics about her research, which mapped the Irishman Creek fault (ICF) and the Forest Creek Fault (FCF) into the lake basin of Lake Tekapo. It has been inferred of the existence of the Tekapo River fault (a north-south structure), from seismic data and exposed geology. (Long ’03)

The ICF is a large feature in the Mackenzie basin and runs along strike to the Alpine Fault. This fault has uplifted the Old man range and is likely to be a part of a broader zone of deformation, the Irishman Creek fault zone (Fox ’87, Cox & Barrell ’07). In the last 5000 years, an interval for reoccurring major events on the ICF of 1290±90yr was determined from dating on scree slopes along the fault trace ( McSaveney ’91).

Initial seismic surveys of Lake Tekapo were conducted by Pickrill and Irwin in ’83. Seismic penetration was approximately 25m below the lake bottom. They classified the sediments, which were sourced from the Godley rive...

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...ation of basement highs, disturbed reflections and orientations parallel to the ICF suggest that we are seeing a continuation of the fault within the lake basin on lines 4,5,6 (basement high west of motuariki basin on L5, two dipping reflector b8&9, apparent dip of 30E )
2)Occur along strike of FCF, suggesting that the basement highs & lake floor features have resulted from movement along this structure (three lake floor highs overlying basement highs and folded sediments)
Topographic highs in a tectonically and glacially active regions may form constructionally by uplift on a fault , or as ROCHES MOUTONNEES by glacial erosion or it may reflect both processes. Upton proposed that these bedrock highs beneath the subsurface of Lake Tekapo are fault-controlled but are being eroded down c.100 ka by glaciers from the Southern Alps contributes to the Roches Moutonnees.

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