Geology Of The Fiordland Area

Turnbull, I.M.; Allibone, A.H.; Jongens, R. (comps) 2010
Geology of the Fiordland area. Lower Hutt: GNS Science. Institute of Geological & Nuclear Sciences 1:250,000 geological map 17, 97 p. + 1 folded map

Abstract

The Fiordland 1:250 000 geological map encompasses the rugged southwestern part of the South Island of New Zealand, including Solander and Little Solander islands in Foveaux Strait. This map area lies directly east of the Alpine Fault, the primary active structure within an east-dipping oblique subduction zone, marking the boundary between the Australian and Pacific plates.

Key Features of the Fiordland Region:

• Topography:
  • Dominated by bush-clad, deeply glaciated mountains.
  • Fiords, many with islands, indent the western coastline.
  • Eastern Fiordland features fiord-like arms of lakes Te Anau and Manapouri, alongside smaller lakes Monowai, Hauroko, and Poteriteri.
  • Extensive raised marine terraces characterize the southern and southwestern coastlines.
• Solander Islands: Eroded remnants of a volcano.

Geological Composition:

• Tectonostratigraphic Terranes:

  • Paleozoic to Mesozoic rocks form parts of at least four terranes.
  • Southwestern Fiordland: Paleozoic metasedimentary and metavolcanic rocks belonging to New Zealand’s Western Province, including Cambrian to Ordovician Buller and Takaka terranes.
  • Western Province rocks extend north to Caswell and George sounds, though terrane affinities are uncertain.
  • Amphibolite facies metamorphism occurred during at least two events.
  • A small Buller terrane area is mapped west of the Alpine Fault.

• Eastern Province Rocks:

  • Fault-bounded slivers of Permian to Triassic Brook Street and Dun Mountain-Maitai terrane volcaniclastic rocks in the Hollyford valley.
  • Mesozoic Loch Burn Formation and Largs Group volcanic and volcaniclastic rocks intercalated with Carboniferous to Cretaceous plutons in eastern Fiordland.

• Median Batholith:

  • Cambrian to Cretaceous plutonic rocks dominate the region.
  • Western part intrudes Early Paleozoic Western Province rocks, absent in the eastern part.
  • Eastern margin intrudes Eastern Province Brook Street terrane, with contacts obscured by Cenozoic faults.

Plutonic Activity:

• Cambrian and Devonian Intrusions: Small dioritic and granitoid plutons.

• Carboniferous Plutons:

  • Ridge and Karamea Suite S-type granitoids.
  • Foulwind Suite A/I type dioritic and granitoid rocks.
  • Paringa Suite I-type gabbroic to granitoid rocks.
  • Tobin Suite I-type granitoid plutons in the eastern batholith.

• Triassic Activity: Dioritic plutons in northeastern Fiordland.

• Jurassic to Early Cretaceous:

  • Darran Suite gabbroic to granodioritic intrusions in both parts of the batholith.
  • Minor Early Cretaceous Rahu Suite granitoids in southwest Fiordland.
  • Separation Point Suite granitoids and Western Fiordland Orthogneiss intrusions.

• Metamorphism:

  • Granulite and eclogite facies metamorphism overprinted some orthogneisses at depths of 50–80 km.
  • Extensional shear zones disrupted intrusive contacts in the later Early Cretaceous.

Sedimentary Rocks:

• Mid-Cretaceous to Cenozoic:

  • Fault-controlled basins (Balleny, Solander, Waiau, Te Anau) with sedimentary sequences up to 8 km thick.
  • Puysegur, Balleny, Annick, and Waiau groups include non-marine and marine clastic rocks.
  • Eastern Fiordland features a thinner sandstone and limestone shelf sequence.

• Late Miocene:

  • Marine sedimentation ceased with Fiordland uplift and Te Anau Basin filling by thick non-marine conglomerates.

• Cenozoic Rocks: Found on Resolution Island, west of the Alpine Fault, and offshore.

(auth/DG)