Geology of Canterbury Region, New Zealand
Encyclopedia
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...
corresponds to the portion of the South Island to the east of the Southern Alps
Southern Alps
The Southern Alps is a mountain range extending along much of the length of New Zealand's South Island, reaching its greatest elevations near the island's western side...
, from the Waiau River in the north, to the Waitaki River
Waitaki River
The Waitaki River is a large river in the South Island of New Zealand, some 110 km long. It is the major river of the Mackenzie Basin.It is a braided river which flows through Lake Benmore, Lake Aviemore and Lake Waitaki. These are ultimately fed by three large glacial lakes, Pukaki, Tekapo,...
in the south.
To the west of the Southern Alps lies 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...
, a major fault boundary, that passes through the South Island from Fiordland
Fiordland
Fiordland is a geographic region of New Zealand that is situated on the south-western corner of the South Island, comprising the western-most third of Southland. Most of Fiordland is dominated by the steep sides of the snow-capped Southern Alps, deep lakes and its ocean-flooded, steep western valleys...
in the south, to the Marlborough Region in the north, where it divides into multiple faults. 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....
lies to the east of the Alpine Fault and the Australian Plate lies to the west. The Pacific Plate is sliding SSW at about 35mm/yr, relative to the Australian Plate, and rising up 10mm/yr, generating the Southern Alps.
The Alpine Fault did not develop until early Miocene times (23 Ma). Ten million years ago the Southern Alps were low hills, and they only became mountainous as recently as 5 million years ago.
To the east of the Southern Alps are the Canterbury Plains
Canterbury Plains
The Canterbury Plains are an area in New Zealand centred to the south of the city of Christchurch in the Canterbury Region. Their northern extremes are at the foot of the Hundalee Hills in the Hurunui District, and in the south they merge into the plains of North Otago beyond the Waitaki...
, formed by the sediment eroded from the Southern Alps. On the coast, just southeast of Christchurch, is Banks Peninsula
Banks Peninsula
Banks Peninsula is a peninsula of volcanic origin on the east coast of the South Island of New Zealand. It has an area of approximately and encompasses two large harbours and many smaller bays and coves...
, composed of two large mainly basaltic Miocene
Miocene
The Miocene is a geological epoch of the Neogene Period and extends from about . The Miocene was named by Sir Charles Lyell. Its name comes from the Greek words and and means "less recent" because it has 18% fewer modern sea invertebrates than the Pliocene. The Miocene follows the Oligocene...
volcanoes.
Basement Rocks
All basement rocks beneath the Canterbury Region belong to the Torlesse Composite (Rakaia and Pahau) TerraneTerrane
A terrane in geology is short-hand term for a tectonostratigraphic terrane, which is a fragment of crustal material formed on, or broken off from, one tectonic plate and accreted or "sutured" to crust lying on another plate...
. They are largely composed of greywacke
Greywacke
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), that accumulated in a deep marine environment, and were accreted to the Gondwana
Gondwana
In paleogeography, Gondwana , originally Gondwanaland, was the southernmost of two supercontinents that later became parts of the Pangaea supercontinent. It existed from approximately 510 to 180 million years ago . Gondwana is believed to have sutured between ca. 570 and 510 Mya,...
continent, before the Tasman sea opened up in late Cretaceous times (80 Ma). They outcrop in the Southern Alps and the foothills. The Rakaia Terrane rocks, of Permian to late Triassic age (300-200 Ma), occur south of Rangiora. The Pahau Terrane rocks, of late Jurassic to early Cretaceous age (160-100 Ma), occur to the north, and are probably derived from the Rakaia Terrane. At the boundary between these two terranes, is the Esk Head Belt, an 11 km wide melange of broken and deformed rocks.
The basement rocks just to the east of the Alpine Fault and to the south of Timaru
Timaru
TimaruUrban AreaPopulation:27,200Extent:Former Timaru City CouncilTerritorial AuthorityName:Timaru District CouncilPopulation:42,867 Land area:2,736.54 km² Mayor:Janie AnnearWebsite:...
have been metamorphosed into Schist
Schist
The schists constitute a group of medium-grade metamorphic rocks, chiefly notable for the preponderance of lamellar minerals such as micas, chlorite, talc, hornblende, graphite, and others. Quartz often occurs in drawn-out grains to such an extent that a particular form called quartz schist is...
.
Southern Alps
The Southern Alps began as sedimentary deposits between 230 and 170 million years ago. The predominantly greywacke formations were uplifted into mountain ranges between 140 and 120 million years ago. From about 26 million years ago, a second continuing period of uplift formed the present-day Southern Alps, driven by the collision of the Pacific tectonic plate with the Australian Plate. The plate boundary is represented by the Alpine Fault which runs slightly west of the main divide of the Southern Alps.Mount Somers Volcanics
Volcanic activity occurred around the Mount SomersMount Somers
Mount Somers is a small town in Canterbury, New Zealand, nestled in the foothills of the Southern Alps. The population in the 2001 census was 2,307. Due to its scenic location, it has seen growth in the number of holiday homes....
area, and nearby foothills, in late Cretaceous times (100-65 Ma). Remnants still exist in the foothills from the Malvern Hills
Malvern Hills
The Malvern Hills are a range of hills in the English counties of Worcestershire, Herefordshire and a small area of northern Gloucestershire, dominating the surrounding countryside and the towns and villages of the district of Malvern...
and the Rangitata River
Rangitata River
The Rangitata River is one of the braided rivers that helped form the Canterbury Plains in southern New Zealand. It flows southeast for 120 kilometres from the Southern Alps, entering the Pacific Ocean 30 kilometres northeast of Timaru...
.
Limestone
Sandstone, mudstone and some limestone were deposited throughout many areas from late Cretaceous to Pliocene times. Oligocene (34-24 Ma) limestone outcrops occur in South Canterbury around the Opihi River area, and in North Canterbury around Omihi, and further north near Waiau.Banks Peninsula
The LytteltonLyttelton, New Zealand
Lyttelton is a port town on the north shore of Lyttelton Harbour close to Banks Peninsula, a suburb of Christchurch on the eastern coast of the South Island of New Zealand....
and Akaroa
Akaroa
Akaroa is a village on Banks Peninsula in the Canterbury region of the South Island of New Zealand, situated within a harbour of the same name—the name Akaroa is Kāi Tahu Māori for 'Long Harbour'.- Overview :...
Harbours correspond to two large overlapping volcanoes, that built Banks Peninsula
Banks Peninsula
Banks Peninsula is a peninsula of volcanic origin on the east coast of the South Island of New Zealand. It has an area of approximately and encompasses two large harbours and many smaller bays and coves...
in late Miocene times (11-6 Ma).
Pliocene Volcanics
BasaltBasalt
Basalt is a common extrusive volcanic rock. It is usually grey to black and fine-grained due to rapid cooling of lava at the surface of a planet. It may be porphyritic containing larger crystals in a fine matrix, or vesicular, or frothy scoria. Unweathered basalt is black or grey...
eruptions occurred near Timaru
Timaru
TimaruUrban AreaPopulation:27,200Extent:Former Timaru City CouncilTerritorial AuthorityName:Timaru District CouncilPopulation:42,867 Land area:2,736.54 km² Mayor:Janie AnnearWebsite:...
and Geraldine
Geraldine
The feminine form of the first name Gerald. Famous women named Geraldine include:*Geraldine Ferraro, United States congresswoman and 1984 Vice Presidential candidate*Geraldine Chaplin, actress*Geraldine Fitzgerald, actress*Geraldine Page, actress...
, around 2.5 Ma.
Glacial Lakes and Moraines
Lakes such as Lake PukakiLake Pukaki
Lake Pukaki is the largest of three roughly parallel alpine lakes running north-south along the northern edge of the Mackenzie Basin on New Zealand's South Island. The others are Lakes Tekapo and Ohau...
and Lake Tekapo
Lake Tekapo
Lake Tekapo is the second-largest of three roughly parallel lakes running north–south along the northern edge of the Mackenzie Basin in the South Island of New Zealand...
in the MacKenzie Country represent the beds of previous glaciers.
Quaternary Deposits
Much of the Canterbury PlainsCanterbury Plains
The Canterbury Plains are an area in New Zealand centred to the south of the city of Christchurch in the Canterbury Region. Their northern extremes are at the foot of the Hundalee Hills in the Hurunui District, and in the south they merge into the plains of North Otago beyond the Waitaki...
are covered by alluvial deposits from the many large rivers coming out of the Southern Alps.
Earthquakes
Generally, there are few earthquakes in the Canterbury Region. However, the Alpine Fault last ruptured in 1717 CE, and a major earthquake on the Alpine Fault can be expected to occur every 200 to 300 years. Liquefaction of the ground can occur up to 150 km from the epicentre for a large earthquake.Notable earthquakes include:
- The 1888 North Canterbury earthquake1888 North Canterbury earthquakeThe 1888 North Canterbury earthquake is the name associated with a severe earthquake which occurred at 4.10 a.m on 1 September 1888 following a sequence of foreshocks that started the previous evening, and whose epicentre was in the North Canterbury region of the South Island of New Zealand.In...
- The 2010 Canterbury earthquake2010 Canterbury earthquakeThe 2010 Canterbury earthquake was a 7.1 magnitude earthquake, which struck the South Island of New Zealand at 4:35 am on local time ....
, 7.1 magnitude, causing widespread damage - The 2011 Canterbury earthquake, 6.3 magnitude, causing widespread damage and deaths
Geological sites of interest
- Drive around Banks Peninsula. Look for Castle Rock, above Heathcote Valley, The Remarkable Dikes near Kaituna Pass, etc.
- Drive from Christchurch to Arthurs Pass, and over the Southern Alps, to GreymouthGreymouthGreymouth is the largest town in the West Coast region in the South Island of New Zealand, and the seat of the Grey District Council. The population of the whole Grey District is , which accounts for % of the West Coast's inhabitants...
. Look for the change from greywacke to schist, as you near the Alpine Fault. - Drive up to Mount Cook, and visit the Hooker GlacierHooker GlacierHooker Glacier is one of several glaciers close to the slopes of Aoraki/Mount Cook in the Southern Alps of New Zealand. Though not as large as its neighbour, the Tasman Glacier, it is still impressive, and is some 11 kilometres in length...
and Tasman GlacierTasman GlacierThe Tasman Glacier is the largest of several glaciers which flow south and east towards the Mackenzie Basin from the Southern Alps in New Zealand's South Island. It is New Zealand's longest glacier.-Geography:...
. - Drive from Christchurch to Hanmer SpringsHanmer SpringsHanmer Springs is a small town in the Canterbury region of the South Island of New Zealand. It is located 65 kilometres southwest of Kaikoura , in the Hurunui District. The town lies on a minor road 9 kilometres north of State Highway 7, the northern route between Christchurch and the West Coast...
, for a hot swim, and see the limestone at Weka Pass on the way.
Maps
Geological maps of New Zealand can be obtained from the New Zealand Institute of Geological and Nuclear Science (GNS ScienceGNS Science
GNS Science is a New Zealand Crown Research Institute. It focuses on geology, geophysics , and nuclear science ....
), a New Zealand Government Research Institute. GNS publishes a 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 Christchurch Area was published in 2008, and the map for the Aoraki Area was published in 2007.
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.