The Tasman Region, and the small adjoining Nelson Region, form one of the more geologically interesting regions of New Zealand. It contains the oldest rocks of anywhere on New Zealand's main islands. It contains all the main terranes that make up New Zealand's basement. These basement rocks include Ultramafic rocks, such as Serpentine and Dunite, and valuable minerals, such as Gold. The Nelson Region is bordered to the south by the Alpine Fault (usually named the Wairau Fault in the Wairau Valley), the main fault forming the boundary between the Pacific Plate and the Indo-Australian Plate, that generated the Southern Alps.
Cartoon cross-section of New Zealand stratigraphy. Cenozoic deformation has been removed for clarity.
The terranes that make up New Zealand's basement are divided up into a Western Province, composed of the Buller and Takaka terranes, and an Eastern Province, composed of the Brook Street, Murihiku, Dun Mountain-Maitai, Caples, Torlesse Composite (Rakaia and Pahau), and Waipapa Composite Terranes. The Median Batholith forms the boundary between the two provinces. All these terranes occur within or near the Nelson Region.
The Buller Terrane forms the basement rocks to the west of the Anatoki Fault (roughly from Whanganui Inlet to Springs Junction), and throughout the West Coast, west of the Alpine Fault, to Milford Sound. The Greenland Group rocks form the base, and are composed of sandstones and mudstones deposited in a submarine fan environment (Late Cambrian-early Ordovician, 505-470 Ma). They are overlain by the Golden Bay Group rocks, composed of quartz sandstone and shale (Ordovician, 490-443 Ma).
The Takaka Terrane forms the basement rocks east of the Anatoki Fault and west of Takaka, the Authur and Matiri Range, south to Springs Junction. The Takaka Terrane is structurally complex, and heavily faulted. The earliest (Middle Cambrian, 518-515 Ma, mostly western) rocks were deposited in an oceanic volcanic arc environment, and represent the oldest rocks in the main islands of New Zealand. Rocks in the Cobb Valley include gabbro and ultramafic rocks that are now largely serpentised. Later (Late Cambrian-Early Devonian, 500-397 Ma, mostly eastern) rocks were deposited in a passive margin environment, and include the Mount Arthur limestone and marble.
The Buller and Takaka Terranes are believed to have been amalgamated around Early or Middle Devonian times, about 390 Ma ago. After amalgamation, in Late Devonian times (370-354 Ma), the Karamea Suite granites were intruded into the Buller Terrane. The Karamea Suite granite often has a distinctive pink colour, due to the K-feldspar megacrysts.
The Median Batholith forms the rocks between the Western and Eastern Provinces. It is assumed to represent a long lived (Late Devonian-Early Cretaceous, 375-110 Ma) Cordilleran batholith, corresponding to a subduction zone along the margin of eastern Australia, before the formation of the Tasman Sea (83-55 Ma). The Median Batholith includes the Riwaka Complex (~375 Ma) and Separation Point Suite (~110 Ma). The Riwaka Complex intruded rocks on the west of Abel Tasman National Park, south to the Baton River Area. The Separation Point Suite corresponds to the granite rocks from Abel Tasman National Park, south to Springs Junction. The basement rocks between Motueka and Nelson, south to Nelson Lakes, are also part of the Median Batholith, but are mainly hidden by the Moutere Depression. However the Median Batholith outcrops around Peppin Island-Nelson City and Nelson Lakes.
The Eastern Province Brook Street, Murihiku, and Dun Mountain-Maitai Central Arc Terranes form narrow successively more easterly strips to the east of the Waimea-Flaxmore Fault System, running from Durville Island in the north, to the Alpine Fault near Nelson Lakes in the south.
The Brook Street Terrane corresponds to a Permian (300-250 Ma) oceanic island arc, and contains well-preserved cross sections through volcanic cones.
The Murihiku Terrane is composed of Triassic to Jurassic (250-145 Ma), relatively undeformed marine sandstone, derived from a volcanic arc.
The Dun Mountain-Maitai Terrane includes the Early Permian (290-256 Ma) Dun Mountain Ophiolite Belt, composed of mafic sea floor basalts and ultramafic mantle rocks. The high nickel and magnesium content inhibits the growth of vegetation on Dun Mountain and Red Hills. These are overlain by Early Permian to Triassic (290-206 Ma) Maitai Group breccia, sandstone, siltstone and limestone.
The Caples Terrane forms much of the Marlborough Sounds, from east of D'Urville Island, to west of Charlotte Sound, and southwest to Nelson Lakes and the Alpine Fault (Wairau Valley). The Caples Terrane was formed in Late Permian to Middle Triassic times (256-227 Ma). The rocks are mostly sandstone and argillite, deposited in a submarine fan, adjacent to an island arc, which have been metamorphosed to schist close to the boundary with the Rakaia Terrane in the southeast.
The Torlesse (Composite) Terane is composed of the Rakaia and Pahau Terranes. The rocks are mostly marine sandstone and mudstone, with the Pahau Terrane being younger (Late Jurassic to Early Cretaceous, 159-99 Ma) than the Rakaia Terrane (Permian to Late Triassic, 290-206 Ma). The Aspiring Lithologic Association schist, south of the Caples Terrane and north of the Alpine Fault, is regarded as belonging to the Rakaia Terrane. The rocks to the south of the Alpine Fault belong to the Torlesse Composite Terrane (Rakaia to the west of Nelson Lakes, Pahau to the east).
The Waipapa (Composite) Terrane is composed of the Hunua and Morrinsville Terranes. The rocks around Picton-Arapawa Island are thought to belong to the Morrinsville Terrane, and are Late Triassic (227-206 Ma) sandstone that has been metamorphosed into schist.
The rocks of western Nelson used to be adjacent to those in Fiordland and Central Otago, before the Alpine Fault was activated in the Early Miocene (23 Ma). The terranes in Nelson match those on the other side of the Alpine Fault, in Fiordland and Central Otago.
Coal and limestone
Most of the Nelson area was above sea level from Late Cretaceous to Middle Eocene time. Coal measures developed in swampland around the Whanganui Inlet in the Late Cretaceous. The coal measures were later covered by sandstone, then conglomerate, corresponding to a braided floodplain. Much of the cover rocks have since been eroded.
Coal measures also developed in swampland over much of western Nelson in Late Eocene times (40-34 Ma). The coal measures are preserved in the Buller Coalfield, the Heaphy River, Takaka, and Richmond. The land then sank, the sea transgressed, and calcareous sandstone, mudstone, and limestone were deposited in Oligocene times (34-24 Ma).
Uplift
The Alpine Fault developed in Early Miocene times (23 Ma), uplift occurred, and deposition changed from limestone to mudstone. Rapid uplift of the Southern Alps occurred in the Late Pliocene (3 Ma). Large quantities of Torlesse derived gravel were generated from the Southern Alps, and are preserved in the Moutere Depression.
Current movement
The Alpine Fault is moving at 3-5mm/year, and the Awatere Fault at 6-8mm/year. The Waimea-Flaxmore Fault System is also active. The Marlborough Sounds are sinking 1-7mm/year. Nelson itself is relatively stable, and the western coast is rising 0-1mm/year.
Geological resources
Alluvial gold has been obtained in the Anatoki, Takaka, Aorere and Paparoa valleys of Golden Bay. Gold has been mined in the Aorangi Mine (Golden Blocks) area, and Johnston's United Mine area. It has also been mined within the Caples Terrane schist.
Chromium and copper have been mined in the Dun Mountain Ophiolite Belt.
Asbestos, talc and magnesite have been mined in the Cobb area.
Coal has been mined in Collingwood, Takaka, Nelson-Richmond, Baton, Heaphy, Karamea and Buller areas.
Mount Arthur marble is used for buildings. Tertiary limestone is quarried to make cement.
The sea to the northwest of the Nelson region are believed to have the potential for oil and gas.
Geological hazards
The main geological hazard is from earthquakes along the Alpine Fault or related faults. Earthquakes in surrounding areas, such as Murchison, Kaikoura, and Wellington also have the potential for damage.
Geological sites of interest
The Cobb Valley, with mafic and ultramafic rocks, serpentine, talc, and asbestos are of great interest.
Abel Tasman National Park is of interest for limestone and marble, Separation Point granite, and the Riwaka Complex diorite and gabbro. From the top of the park, it is possible to see Harwoods Hole, a large vertical shaft that goes down to the limestone cave system of Takaka Hill.
The Arthur Range is a good place to see Mount Arthur marble.
The Bryant Range is a good place to see the Central Arc Terranes. Red Hill and Dun Mountain are good places to see the effects of ultramafic rocks on vegetation.
A trip on the inter-island ferry provides a good way to see the Marlborough Sounds.
The Alpine Fault can be seen in the Wairau Valley, between Blenheim and Nelson Lakes.
The effects of glaciation can be seen around Nelson Lakes.
Maps
Geological maps of New Zealand can be obtained from the New Zealand Institute of Geological and Nuclear Science (GNS Science), a New Zealand Government Research Institute. [2]
GNS provides a free Map of New Zealand's Geological Foundations.[3]
The main maps are the 1: 250 000 QMap series, which will be completed as a series of 21 maps and booklets in 2010.[needs update] Low resolution versions of these maps (without the associated booklet) can be downloaded from the GNS site for free.[4]
The map for the Nelson Area was published in 1998.[5] The map for the Wellington Area was published in 2000.[6] The map for the Greymouth Area was published in 2002.[7] The map for the Kaikoura Area was published in 2006.[8]
In geology, a terrane is a crust fragment formed on a tectonic plate and accreted or "sutured" to crust lying on another plate. The crustal block or fragment preserves its own distinctive geologic history, which is different from that of the surrounding areas—hence the term "exotic" terrane. The suture zone between a terrane and the crust it attaches to is usually identifiable as a fault. A sedimentary deposit that buries the contact of the terrane with adjacent rock is called an overlap formation. An igneous intrusion that has intruded and obscured the contact of a terrane with adjacent rock is called a stitching pluton.
The geology of Antarctica covers the geological development of the continent through the Archean, Proterozoic and Phanerozoic eons.
The Torlesse Composite Terrane is a plate tectonic terrane forming part of the South Island of New Zealand. It contains the Rakaia, Aspiring and Pahau Terranes and the Esk Head Belt. Greywacke is the dominant rock type of the composite terrane; argillite is less common and there are minor basalt occurrences. The Torlesse Composite Terrane is found east of the Alpine Fault in the Southern Alps of New Zealand. Its southern extent is a cryptic boundary with the Caples Terrane within the Haast Schists in Central Otago. It is named for the Torlesse Range in Canterbury.
The Haast Schist, which contains both the Alpine and Otago Schist, is a metamorphic unit in the South Island of New Zealand. It extends from Central Otago, along the eastern side of the Alpine Fault to Cook Strait. There are also isolated outcrops of the Haast Schist within the central North Island. The schists were named after Haast Pass on the West Coast. The Haast Schist can be divided geographically from north to south into the Kaimanawa, Terawhiti, Marlborough, Alpine, Otago and Chatham schist.
The geology of New Zealand is noted for its volcanic activity, earthquakes and geothermal areas because of its position on the boundary of the Australian Plate and Pacific Plates. New Zealand is part of Zealandia, a microcontinent nearly half the size of Australia that broke away from the Gondwanan supercontinent about 83 million years ago. New Zealand's early separation from other landmasses and subsequent evolution have created a unique fossil record and modern ecology.
The Auckland Region of New Zealand is built on a basement of greywacke rocks that form many of the islands in the Hauraki Gulf, the Hunua Ranges, and land south of Port Waikato. The Waitākere Ranges in the west are the remains of a large andesitic volcano, and Great Barrier Island was formed by the northern end of the Coromandel Volcanic Zone. The Auckland isthmus and North Shore are composed of Waitemata sandstone and mudstone, and portions of the Northland Allochthon extend as far south as Albany. Little Barrier Island was formed by a relatively isolated andesitic volcano, active around 1 to 3 million years ago.
The Waikato and King Country regions of New Zealand are built upon a basement of greywacke rocks, which form many of the hills. Much of the land to the west of the Waikato River and in the King Country to the south has been covered by limestone and sandstone, forming bluffs and a karst landscape. The volcanic cones of Karioi and Pirongia dominate the landscape near Raglan and Kawhia Harbours. To the east, the land has been covered with ignimbrite deposits from the Taupo Volcanic Zone. Large amounts of pumice from the Taupo Volcanic Zone have been deposited in the Waikato Basin and Hauraki Plains.
The Taranaki Region of New Zealand is built upon the Median Batholith in the West, and Greywacke Rocks in the East. However, no rocks older than Miocene times are visible at the surface. The dominant feature of the Taranaki Region is the andesitic stratovolcano of Mount Taranaki, which is only about 130,000 years old. The dissected hill country to the East of the Taranaki Peninsula, and West of the Central Volcanic Plateau is composed of soft Miocene to Pleistocene sandstone and mudstone. The coastal lowlands around Wanganui to the South have well-developed Quaternary marine terraces, and coastal sand dunes.
The Wellington Region of New Zealand has a foundation of Torlesse Greywacke rocks, that make up the Tararua and Rimutaka Ranges, that go from Wellington in the south to the Manawatū Gorge, where they are renamed as the Ruahine Ranges, and continue further north-northeast, towards East Cape. To the west of the Tararua Ranges are the Manawatū coastal plains. To the east of the Ruahine Ranges is the Wairarapa-Masterton Basin, then the Eastern Uplands that border the eastern coast of the North Island from Cape Palliser to Napier.
The Raukumara Region of New Zealand corresponds to the East Cape of the North Island, and associated mountain ranges.
Canterbury in New Zealand is the portion of the South Island to the east of the Southern Alps / Kā Tiritiri o te Moana, from the Waiau Uwha River in the north, to the Waitaki River in the south.
New Zealand's Northland Region is built upon a basement consisting mainly of greywacke rocks, which are exposed on the eastern side of the peninsula. In-place Eocene coal measures crop out at Kamo, near Whangarei, and Oligocene limestone crops out at Hikurangi, near Whangarei.
The Wairau Fault is an active dextral strike-slip fault in the northeastern part of South Island, New Zealand. It forms part of the Marlborough Fault System, which accommodates the transfer of displacement along the oblique convergent boundary between the Indo-Australian Plate and Pacific Plate, from the transform Alpine Fault to the Hikurangi Trench subduction zone.
The Lhasa terrane is a terrane, or fragment of crustal material, sutured to the Eurasian Plate during the Cretaceous that forms present-day southern Tibet. It takes its name from the city of Lhasa in the Tibet Autonomous Region, China. The northern part may have originated in the East African Orogeny, while the southern part appears to have once been part of Australia. The two parts joined, were later attached to Asia, and then were impacted by the collision of the Indian Plate that formed the Himalayas.
The Dun Mountain-Maitai Terrane comprises the Dun Mountain Ophiolite Belt, Maitai Group and Patuki Mélange. The Dun Mountain Ophiolite is an ophiolite of Permian age located in New Zealand's South Island. Prehistorically this ophiolite was quarried by Māori for both metasomatized argillite and pounamu (jade) which was used in the production of tools and jewellery.
Dun Mountain is a mountain in the Richmond Range near the city of Nelson in the Tasman District of New Zealand's South Island. It is located between the catchments of the Pelorus, Maitai and Roding Rivers. The mountain is named for its brown (Dun) colour. The colour is caused by the ultramafic rock which forms the mountain. Ultramafic Rock weathers to this colour and plant growth is also stunted due to the soils high heavy metal content. The ultramafic rock formed in the earth's mantle in the Permian and is now part of the Dun Mountain Ophiolite Belt.
The Takaka Terrane is a Paleozoic terrane that outcrops in the South Island of New Zealand. It is most extensively exposed within the Kahurangi National Park in the Tasman District. The terrane is mostly made up of marble and volcanic rocks but is highly variable in composition. It ranges in age from mid-Cambrian to Devonian time, including New Zealand's oldest rocks, which are found in the Cobb Valley in north-west Nelson. The Cobb Valley is also the location of "Trilobite Rock" a glacial dropstone made from the moulted exoskeletons of trilobites. Asbestos was mined in the Cobb Valley from the Takaka Terrene between the late 1880s and 1917. The Takaka Terrane is highly deformed and has been intruded by many batholiths.
This is a list of the units into which the rock succession of New Zealand is formally divided. As new geological relationships have been discovered new names have been proposed and others are made obsolete. Not all these changes have been universally adopted. This table is based on the 2014 New Zealand Stratigraphic Lexicon (Litho2014). However, obsolete names that are still in use and names postdating the lexicon are included if it aids in understanding.
The geology of the West Coast of New Zealand's South Island is divided in two by the Alpine Fault, which runs through the Region in a North-East direction. To the West of the fault Paleozoic basement rocks are interluded by plutones and both are unconformably covered in a sedimentary sequence. To the East of the Alpine Fault are the Mesozoic Alpine Schist and Greywacke of the Southern Alps. There are numerous active faults throughout the region.
The Southland Syncline is a major geological structure located in the Southland Region of New Zealand's South Island. The syncline folds the Mesozoic greywackes of the Murihiku Terrane. The northern limb of the fold is steep to overturned, while the southern limb dips shallowly to the northeast. The axial plan dips to the northeast and the axis plunges to the southeast.
Graham, Ian J. et al.;A continent on the move: New Zealand geoscience into the 21st century - The Geological Society of New Zealand in association with GNS Science, 2008. ISBN978-1-877480-00-3
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