Geology of the Fiordland area : scale 1:250,000 Digital Download

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Turnbull, I.M.; Allibone, A.H.; Jongens, R. (comps) 2010 Geology of the Fiordland area : scale 1:250,000 Institute of Geological & Nuclear Sciences 1:250,000 geological map. 17


Abstract: The Fiordland 1:250 000 geological map covers the rugged southwestern part of the South Island of New Zealand, and includes Solander and Little Solander islands in Foveaux Strait. The map area lies immediately east of the Alpine Fault, the main active structure within an east-dipping oblique subduction zone that forms the boundary between the Australian and Pacific plates. Fiordland topography is dominated by bush-clad and deeply glaciated mountains. Fiords, many studded with islands, indent the western coast. Eastern Fiordland is also indented by the fiord-like arms of lakes Te Anau and Manapouri, and the smaller lakes Monowai, Hauroko and Poteriteri further south. Extensive raised marine terraces typify the southern and southwestern coastlines. The Solander Islands are the eroded remnants of a volcano. The map area covers a wide range of Paleozoic to Mesozoic rocks that form parts of at least four tectonostratigraphic terranes. Southwestern Fiordland has a basement of Paleozoic metasedimentary and metavolcanic rocks of New Zealand’s Western Province, including the Cambrian to Ordovician Buller and Takaka terranes. Similar rocks extend as far north as Caswell and George sounds in western and central Fiordland, although their terrane affinities are uncertain. Most of these Western Province rocks have been deformed and metamorphosed to amphibolite facies during at least two events. A small area of Buller terrane is also mapped west of the Alpine Fault. Fault-bounded slivers of Permian to Triassic Brook Street and Dun Mountain-Maitai terrane volcaniclastic rocks of the Eastern Province occur in the Hollyford valley. Volcanic and volcaniclastic rocks of the Mesozoic Loch Burn Formation and Largs Group are intercalated with Carboniferous to Cretaceous plutons in eastern Fiordland. Much of Fiordland is underlain by Cambrian to Cretaceous plutonic rocks of the Median Batholith. The western (inboard) part of the batholith intrudes Early Paleozoic metasedimentary rocks of the Western Province, but these metasedimentary rocks are not recorded from the eastern (outboard) part of the batholith. The eastern margin of the batholith intruded the Eastern Province Brook Street terrane, but the contact is now largely obscured by Cenozoic faults. The oldest plutonic rocks within the batholith are small dioritic and granitoid intrusions of Cambrian and Devonian age. Carboniferous plutonic rocks are more abundant, and include Ridge and Karamea Suite S-type granitoids, Foulwind Suite A/I type dioritic and granitoid rocks, and Paringa Suite I-type gabbroic to granitoid rocks. These Carboniferous plutons form an extensive belt through the centre of Fiordland in the western part of the Median Batholith. Carboniferous Tobin Suite I-type granitoid plutons also occur within the eastern part of the batholith. The next known plutonic activity is 100 million years younger, in the Triassic, when dioritic plutons were emplaced in northeastern Fiordland. During the Jurassic to Early Cretaceous, much larger volumes of heterogeneous Darran Suite gabbroic to granodioritic rocks were intruded into both outboard and inboard parts of the Median Batholith. Minor Early Cretaceous Rahu Suite granitoid rocks were emplaced in southwest Fiordland. Early Cretaceous plutonism continued with the emplacement of the granitoid Separation Point Suite and dioritic Western Fiordland Orthogneiss, the former extending throughout Fiordland. Granulite and eclogite facies metamorphism overprinted some Western Fiordland orthogneisses at depths of 50–80 km. Intrusive contacts between Western Fiordland Orthogneiss plutons and adjacent metasedimentary rocks were locally disrupted by extensional shear zones in the later Early Cretaceous. In eastern and southern Fiordland, and in western Foveaux Strait, basement rocks are unconformably overlain by mid-Cretaceous and Cenozoic sedimentary rocks that were deposited in the fault-controlled Balleny, Solander, Waiau and Te Anau basins. The sedimentary rocks are subdivided into the Puysegur, Balleny, Annick and Waiau groups, and form sequences of non-marine and marine clastic sedimentary rocks up to 8 km thick. A thinner sandstone and limestone shelf sequence extends discontinuously along the eastern margin of Fiordland. Marine sedimentation ended in the Late Miocene, with the uplift of Fiordland and the filling of the Te Anau Basin by thick non-marine conglomerates. Cenozoic rocks also occur on Resolution Island, west of the Alpine Fault, and offshore. (auth/DG)