Geology of Wellington Region
Encyclopedia
The Wellington Region
of New Zealand
has a foundation of Torlesse Greywacke
rocks, that make up the Tararua
and Rimutaka Range
s, that go from Wellington
in the south to the Manawatu 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 Manawatu 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.
To the east of the North Island is the Hikurangi Trough, a collision zone between the Pacific Plate
and the Australian Plate. The Pacific Plate is being subducted under the Australian Plate, compressing the Wellington Region, and causing the North Island Fault System, and a series of SSW-NNE trending basins and ranges, including the Tararua and Rimutaka Ranges, and the Wairarapa-Masterton Basin. Successively newer rocks have been accreted to the east coast.
The Wellington Region is prone to major earthquakes, the biggest in historical times being the magnitude 8.2 1855 Wairarapa Earthquake
.
(hardened sandstone and mudstone), but also contain Chert
, and Pillow lava
s.
In the Wellington Region, the Torlesse Composite Terrane is composed of two subterranes, the Rakaia Terrane (late Triassic
to early Jurassic
, 230-180 Ma), to the west of the Ruahine Ranges, and the Pahau Terrane (late Jurassic
to early Cretaceous
, 180-100 Ma), to the east. Major faults such as the Wellington Fault
and Wairarapa Fault
lie close to the boundary between the terranes. At the boundary between these two terranes, is the Esk Head Belt, a 20 km wide melange of rocks, broken and deformed by earthquakes along the fault lines near the boundary.
Further to the east of the Wairapa-Masterton Basin, are successively younger Cretaceous
(140-65 Ma) sandstones and mudstones (sometimes called the Waioeka Terrane), that can be regarded as part of the Torlesse Composite Terrane. There seems to be some disagreement on where to place the boundary between basement rocks and overlying rocks, and the decision seems to be based on the degree of induration. In the east, even younger and softer sandstones and mudstones occur.
(5-2 Ma) limestone occurs to the east of the Wairarapa-Masterton Basin, and around Pahiatua, and the Puketoi Range.
. Near the fault line, the beach rose about 6 m in this earthquake, and horizontal movement was about 12 m. Wellington's Basin Reserve sports ground sits on land lifted by this earthquake; the area had previously been part of a waterway that led into the harbour.
Other major faults include the Alpine Fault
, Ohariu Fault, Otaki Forks Fault, and Wairangi Fault.
The Wairarapa Fault has an average horizontal slip rate of 6.7–10 mm/year, and vertical change of 1.7 mm/year. The Wellington and Awatere Fault
s have similar rates of movement.
Beaches around Wellington and Turakirae Head show multiple raised platforms corresponding to previous earthquakes.
GNS provides a free Map of New Zealand's Geological Foundations.GNS Map of New Zealand's Geological Foundations
The main maps are the 1 : 250 000 QMap series, which will be completed as a series of 21 maps and booklets in 2010. Low resolution versions of these maps (without the associated booklet) can be downloaded from the GNS site for free. The map for the Wellington Area was published in 2000
,
and the map for the Wairarapa Area was published in 2002
.
There is also a 1 : 50 000 geological map of the Wellington urban area, together with an associated booklet.
Wellington Region
The Wellington region of New Zealand occupies the southern end of the North Island.-Governance:The official Wellington Region, as administered by the Wellington Regional Council covers the conurbation around the capital city, Wellington, and the cities of Lower Hutt, Porirua, and Upper Hutt, each...
of New Zealand
New Zealand
New Zealand is an island country in the south-western Pacific Ocean comprising two main landmasses and numerous smaller islands. The country is situated some east of Australia across the Tasman Sea, and roughly south of the Pacific island nations of New Caledonia, Fiji, and Tonga...
has a foundation of Torlesse Greywacke
Torlesse Greywacke
Torlesse Greywacke is a type of sedimentary rock. It is a hard and rather drab grey sandstone that is found in New Zealand. Torlesse Greywacke is found east of the Alpine Fault in the Southern Alps of New Zealand...
rocks, that make up the Tararua
Tararua Range
The Tararua Range is one of several mountain ranges in the North Island of New Zealand which form a ridge running parallel with the east coast of the island between East Cape and Wellington....
and Rimutaka Range
Rimutaka Range
The Rimutaka Range is one of several mountain ranges in the North Island of New Zealand which form a ridge running parallel with the east coast of the island between East Cape and Wellington.The ridge is at its most pronounced in the southern part of the island, where it consists of the Ruahine,...
s, that go from Wellington
Wellington
Wellington is the capital city and third most populous urban area of New Zealand, although it is likely to have surpassed Christchurch due to the exodus following the Canterbury Earthquake. It is at the southwestern tip of the North Island, between Cook Strait and the Rimutaka Range...
in the south to the Manawatu Gorge
Manawatu Gorge
The Manawatu Gorge runs between the Ruahine and Tararua Ranges of the North Island of New Zealand, linking the Manawatu and Hawke's Bay regions...
, 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 Manawatu 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.
To the east of the North Island is the Hikurangi Trough, a collision zone between the Pacific Plate
Pacific Plate
The Pacific Plate is an oceanic tectonic plate that lies beneath the Pacific Ocean. At 103 million square kilometres, it is the largest tectonic plate....
and the Australian Plate. The Pacific Plate is being subducted under the Australian Plate, compressing the Wellington Region, and causing the North Island Fault System, and a series of SSW-NNE trending basins and ranges, including the Tararua and Rimutaka Ranges, and the Wairarapa-Masterton Basin. Successively newer rocks have been accreted to the east coast.
The Wellington Region is prone to major earthquakes, the biggest in historical times being the magnitude 8.2 1855 Wairarapa Earthquake
1855 Wairarapa earthquake
The 1855 Wairarapa earthquake occurred on 23 January at about 9 p.m. In Wellington, close to the epicenter, shaking lasted for at least 50 seconds. The magnitude of the earthquake is estimated to have been in the range 8.1-8.3, the most powerful recorded in New Zealand since systematic European...
.
Basement rocks
All basement rocks beneath the Wellington Region belong to the Torlesse Composite Terrane. They are largely composed of GreywackeGreywacke
Greywacke or Graywacke is a variety of sandstone generally characterized by its hardness, dark color, and poorly sorted angular grains of quartz, feldspar, and small rock fragments or lithic fragments set in a compact, clay-fine matrix. It is a texturally immature sedimentary rock generally found...
(hardened sandstone and mudstone), but also contain Chert
Chert
Chert is a fine-grained silica-rich microcrystalline, cryptocrystalline or microfibrous sedimentary rock that may contain small fossils. It varies greatly in color , but most often manifests as gray, brown, grayish brown and light green to rusty red; its color is an expression of trace elements...
, and Pillow lava
Pillow lava
Pillow lavas are lavas that contain characteristic pillow-shaped structures that are attributed to the extrusion of the lava under water, or subaqueous extrusion. Pillow lavas in volcanic rock are characterized by thick sequences of discontinuous pillow-shaped masses, commonly up to one metre in...
s.
In the Wellington Region, the Torlesse Composite Terrane is composed of two subterranes, the Rakaia Terrane (late Triassic
Triassic
The Triassic is a geologic period and system that extends from about 250 to 200 Mya . As the first period of the Mesozoic Era, the Triassic follows the Permian and is followed by the Jurassic. Both the start and end of the Triassic are marked by major extinction events...
to early Jurassic
Jurassic
The Jurassic is a geologic period and system that extends from about Mya to Mya, that is, from the end of the Triassic to the beginning of the Cretaceous. The Jurassic constitutes the middle period of the Mesozoic era, also known as the age of reptiles. The start of the period is marked by...
, 230-180 Ma), to the west of the Ruahine Ranges, and the Pahau Terrane (late Jurassic
Jurassic
The Jurassic is a geologic period and system that extends from about Mya to Mya, that is, from the end of the Triassic to the beginning of the Cretaceous. The Jurassic constitutes the middle period of the Mesozoic era, also known as the age of reptiles. The start of the period is marked by...
to early Cretaceous
Cretaceous
The Cretaceous , derived from the Latin "creta" , usually abbreviated K for its German translation Kreide , is a geologic period and system from circa to million years ago. In the geologic timescale, the Cretaceous follows the Jurassic period and is followed by the Paleogene period of the...
, 180-100 Ma), to the east. Major faults such as the Wellington Fault
Wellington Fault
The Wellington Fault is an active seismic fault in the southern part of the North Island of New Zealand. It is a dextral strike-slip fault with variable amounts of vertical movement causing uplift to the northwest, as expressed by a series of ranges...
and Wairarapa Fault
Wairarapa Fault
The Wairarapa Fault is an active seismic fault in the southern part of the North Island of New Zealand. It is a dextral strike-slip fault with a component of uplift to the northwest as expressed by the Rimutaka Range...
lie close to the boundary between the terranes. At the boundary between these two terranes, is the Esk Head Belt, a 20 km wide melange of rocks, broken and deformed by earthquakes along the fault lines near the boundary.
Further to the east of the Wairapa-Masterton Basin, are successively younger Cretaceous
Cretaceous
The Cretaceous , derived from the Latin "creta" , usually abbreviated K for its German translation Kreide , is a geologic period and system from circa to million years ago. In the geologic timescale, the Cretaceous follows the Jurassic period and is followed by the Paleogene period of the...
(140-65 Ma) sandstones and mudstones (sometimes called the Waioeka Terrane), that can be regarded as part of the Torlesse Composite Terrane. There seems to be some disagreement on where to place the boundary between basement rocks and overlying rocks, and the decision seems to be based on the degree of induration. In the east, even younger and softer sandstones and mudstones occur.
Limestone
PliocenePliocene
The Pliocene Epoch is the period in the geologic timescale that extends from 5.332 million to 2.588 million years before present. It is the second and youngest epoch of the Neogene Period in the Cenozoic Era. The Pliocene follows the Miocene Epoch and is followed by the Pleistocene Epoch...
(5-2 Ma) limestone occurs to the east of the Wairarapa-Masterton Basin, and around Pahiatua, and the Puketoi Range.
Earthquakes
The Wellington Region is prone to major earthquakes, the biggest in historical times being the magnitude 8.2 1855 Wairarapa Earthquake1855 Wairarapa earthquake
The 1855 Wairarapa earthquake occurred on 23 January at about 9 p.m. In Wellington, close to the epicenter, shaking lasted for at least 50 seconds. The magnitude of the earthquake is estimated to have been in the range 8.1-8.3, the most powerful recorded in New Zealand since systematic European...
. Near the fault line, the beach rose about 6 m in this earthquake, and horizontal movement was about 12 m. Wellington's Basin Reserve sports ground sits on land lifted by this earthquake; the area had previously been part of a waterway that led into the harbour.
Other major faults include the Alpine Fault
Alpine Fault
The Alpine Fault is a geological fault, more specifically known as a right-lateral strike-slip fault, that runs almost the entire length of New Zealand's South Island. It forms a transform boundary between the Pacific Plate and the Indo-Australian Plate. Earthquakes along the fault, and the...
, Ohariu Fault, Otaki Forks Fault, and Wairangi Fault.
The Wairarapa Fault has an average horizontal slip rate of 6.7–10 mm/year, and vertical change of 1.7 mm/year. The Wellington and Awatere Fault
Awatere Fault
The Awatere 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,...
s have similar rates of movement.
Beaches around Wellington and Turakirae Head show multiple raised platforms corresponding to previous earthquakes.
Geological Sites, etc. Worth Visiting
- The Te Papa Tongarewa Museum of New Zealand in Wellington is worth a visit.
- GNS Science, 1 Fairway Drive, Avalon, Lower Hutt 5010, sells geological maps and books.
- Visit Turakirae Head, to see the raised beaches.
- Drive from Wellington to the Hutt Valley to see the Wellington Fault.
- Drive from Wellington to Porirua to see Torlesse Greywacke.
- Visit Red Rocks Scientific Reserve, to red, green and grey mudstones from the Red Rocks sequence.
- Visit the Putangirua Pinnacles Reserve, in southern Wairarapa, to see erosion formations formed from Miocene conglomerate.
- Visit the Puketoi Range and Kohinui for Pliocene limestone scarps.
- Thrust Creek represents the position of the West Wairarapa Fault, where the land rose 2.7 metres vertically, and 12 metres horizontally in the 1855 earthquake.
- Putangirua Pinnacles have a fantastic example of an eroded landscape.
- Cape Palliser has pillow lavas.
- White Rock contains trace fossils of a burrowing organism. Ngapotiki fan is an alluvial fan that is being cut away by the sea at its base.
- Kaiwhata River Mouth has fossil treestumps, from land that has been inundated by the sea at the end of the last ice age, then uncovered as the land has risen due to tectonic forces.
- Cape Turnagain has siltstone cliffs, topped by a protective layer of limestone containing fossil scallops. Castlepoint also has many fossils.
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.GNS provides a free Map of New Zealand's Geological Foundations.GNS Map of New Zealand's Geological Foundations
The main maps are the 1 : 250 000 QMap series, which will be completed as a series of 21 maps and booklets in 2010. Low resolution versions of these maps (without the associated booklet) can be downloaded from the GNS site for free. The map for the Wellington Area was published in 2000
,
and the map for the Wairarapa Area was published in 2002
.
There is also a 1 : 50 000 geological map of the Wellington urban area, together with an associated booklet.
Further reading
- 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. ISBN 9781877480003
- Plate Tectonics for Curious Kiwis - Aitken, Jefley; GNS Science, 1996. ISBN 0-478-09555-4.
- Rugged landscape : the geology of central New Zealand, including Wellington, Wairarapa, Manawatu and the Marlborough Sounds,Graeme R. Stevens, Reed 1990.
- Reading the rocks : a guide to geological features of the Wairarapa Coast - Homer, Lloyd; Moore, Phil & Kermode, Les; Landscape Publications and the Institute of Geological and Nuclear Sciences, 1989. ISBN 0908800002.
- On shaky ground : a geological guide to the Wellington metropolitan region, Graeme Stevens, Geological Society of New Zealand.