QM 15 Aoraki
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.
The break-up of Gondwanaland began in the Early Cretaceous with associated igneous activity, extension and subsidence. Progressive regional submergence in the eastern part of the map area through the Late Cretaceous and Paleogene was accompanied by deposition of a terrestrial to marine transgressive sequence of conglomerates, sandstones and mudstones. The extent of land reached a minimum in the middle Oligocene, with widespread deposition of calcareous sediments in the surrounding seas. Development of the Australian-Pacific plate boundary started in the Early Miocene. Associated tectonic deformation caused subsidence west of the Alpine Fault, with deposition of marine sediments.
Meanwhile, to the east, there was progressive emergence of the land and the formation of ranges and basins, with concomitant erosion and deposition. Uplift by folding and faulting continues to the present day throughout much of the central part of the map area, while to the east, subsidence occurs beneath parts of the Canterbury Plains and offshore. Glacial-interglacial climatic fluctuations in the late Neogene resulted in the widespread deposition of unconsolidated Quaternary sediments. Metallic mineral occurrences are mostly restricted to South Westland, where hard-rock and alluvial gold deposits and mineral-rich beach sands have been worked. Pounamu/greenstone is a locally important non-metallic mineral in South Westland.
Coal, clay and sand have been extracted from the Cretaceous-Cenozoic sedimentary sequence of Canterbury, and there is potential for hydrocarbons to be discovered in this sequence beneath the Canterbury Plains or offshore. There are vast resources of limestone and aggregate in Canterbury. Shallow groundwater resources are substantial and are widely utilised in the low-rainfall areas east of the Southern Alps.
Deeper groundwater resources are not well known but may be needed for future urban and rural development. The Aoraki map area is vulnerable to significant geological hazards, particularly earthquakes associated with the Alpine Fault and other active faults, with potential for strong ground shaking, lan dsliding, liquefaction and ground rupture. Slope instability, including rock avalanches, rockfalls and debris flows, is a major hazard in hill and mountain terrain. Erosion, flooding and sedimentation hazards exist near watercourses. Low-lying areas along the coast and lake shores are potentially at risk from tsunamis.