Geology Of The Aoraki Area

Cox, S.C.; Barrell, D.J.A. (comps) 2007
Geology of the Aoraki area. Lower Hutt: GNS Science.
Institute of Geological & Nuclear Sciences 1:250,000 geological map 15
71 p. + 1 folded map

Abstract

The Aoraki 1:250 000 geological map covers 24 000 km² of South Westland and central parts of the Canterbury region in the South Island of New Zealand. It encompasses the highest part of the Southern Alps, including 3754-m high Aoraki/Mt Cook.

The map area is crossed by the Alpine Fault – a major strike-slip fault that marks the boundary between the Australian and Pacific tectonic plates. Neogene movement along the plate boundary has brought together two different pre-Cretaceous geological provinces:

• Northwest of the Alpine Fault:
  Paleozoic metasedimentary and plutonic basement rocks are fragments of the Gondwanaland supercontinent.

• Southeast of the Alpine Fault:
  The Torlesse composite terrane is a thick, deformed package of Carboniferous-Jurassic sedimentary and metasedimentary basement rocks that were accreted to the Gondwanaland margin.

Geological History

• Early Cretaceous:
  The break-up of Gondwanaland began, accompanied by igneous activity, extension, and subsidence.

• Late Cretaceous and Paleogene:
  Progressive regional submergence in the eastern part of the map area led to deposition of a terrestrial to marine transgressive sequence of conglomerates, sandstones, and mudstones.

• Middle Oligocene:
  Land extent reached a minimum, with widespread deposition of calcareous sediments in surrounding seas.

• Early Miocene:
  Development of the Australian-Pacific plate boundary began, causing:

  • West of the Alpine Fault: Subsidence and deposition of marine sediments.
  • East of the Alpine Fault: Progressive emergence of land, formation of ranges and basins, erosion, and deposition.

• Present Day:
  Uplift by folding and faulting continues throughout much of the central map area, while subsidence occurs beneath parts of the Canterbury Plains and offshore.

Quaternary and Mineral Resources

• Late Neogene climatic fluctuations:
  Glacial-interglacial periods resulted in widespread deposition of unconsolidated Quaternary sediments.

• Metallic mineral occurrences:

  • Mostly restricted to South Westland.
  • Includes hard-rock and alluvial gold deposits and mineral-rich beach sands.
  • Pounamu/greenstone is a locally important non-metallic mineral.

• Canterbury resources:

  • Coal, clay, and sand extracted from the Cretaceous-Cenozoic sedimentary sequence.
  • Potential for hydrocarbons beneath the Canterbury Plains or offshore.
  • Vast resources of limestone and aggregate.

• Groundwater resources:

  • Substantial shallow groundwater resources widely utilised in low-rainfall areas east of the Southern Alps.
  • Deeper groundwater resources are less known but may be needed for future development.

Geological Hazards

The Aoraki map area is vulnerable to significant geological hazards:

• Earthquakes:
  Associated with the Alpine Fault and other active faults, with potential for strong ground shaking, landsliding, liquefaction, and ground rupture.

• Slope instability:
  Includes rock avalanches, rockfalls, and debris flows in hill and mountain terrain.

• Watercourse hazards:
  Erosion, flooding, and sedimentation near rivers and streams.

• Coastal and lake hazards:
  Low-lying areas are potentially at risk from tsunamis.