New Zealand's Northland Region is built upon a

basement A basement or cellar is one or more floors of a building that are completely or partly below the ground floor. It generally is used as a utility space for a building, where such items as the furnace, water heater, breaker panel or fuse box, ...

consisting mainly of greywacke rocks, which are exposed on the eastern side of the peninsula. In-place

Eocene The Eocene ( ) Epoch is a geological epoch (geology), epoch that lasted from about 56 to 33.9 million years ago (mya). It is the second epoch of the Paleogene Period (geology), Period in the modern Cenozoic Era (geology), Era. The name ''Eocene' ...

coal measures crop out at Kamo, near Whangarei, and

Oligocene The Oligocene ( ) is a geologic epoch of the Paleogene Period and extends from about 33.9 million to 23 million years before the present ( to ). As with other older geologic periods, the rock beds that define the epoch are well identified but the ...

limestone crops out at Hikurangi, near Whangarei. A

subduction Subduction is a geological process in which the oceanic lithosphere is recycled into the Earth's mantle at convergent boundaries. Where the oceanic lithosphere of a tectonic plate converges with the less dense lithosphere of a second plate, the ...

zone is believed to have existed to the northeast of Northland in early

Miocene The Miocene ( ) is the first geological epoch of the Neogene Period and extends from about (Ma). The Miocene was named by Scottish geologist Charles Lyell; the name comes from the Greek words (', "less") and (', "new") and means "less recen ...

times, causing the Northland Allochthon to thrust over much of the peninsula and

volcanic belt A volcanic belt is a large volcanically active region. Other terms are used for smaller areas of activity, such as volcanic fields. Volcanic belts are found above zones of unusually high temperature () where magma is created by partial melting ...

s to develop on either side of the peninsula. Intra-plate basaltic volcanic activity has occurred around Kaikohe, the Bay of Islands, and Whangarei since late Miocene times.

Sand dune A dune is a landform composed of wind- or water-driven sand. It typically takes the form of a mound, ridge, or hill. An area with dunes is called a dune system or a dune complex. A large dune complex is called a dune field, while broad, fl ...

s sourced from volcanoes further south occupy much of the western coast, and the Aupouri Peninsula joins previously separate islands to the mainland to form a large tombolo. New Zealand geology map with key

Basement rocks

As with most of New Zealand, the basement rocks of the Northland Region are mainly composed of greywacke (

indurated Friability ( ), the condition of being friable, describes the tendency of a solid substance to break into smaller pieces under duress or contact, especially by rubbing. The opposite of friable is indurate. Substances that are designated hazardous, ...

sandstone Sandstone is a clastic sedimentary rock composed mainly of sand-sized (0.0625 to 2 mm) silicate grains. Sandstones comprise about 20–25% of all sedimentary rocks. Most sandstone is composed of quartz or feldspar (both silicates) ...

), argillite, and

chert Chert () is a hard, fine-grained sedimentary rock composed of microcrystalline or cryptocrystalline quartz, the mineral form of silicon dioxide (SiO2). Chert is characteristically of biological origin, but may also occur inorganically as a prec ...

, together with volcanic rocks, such as

basalt Basalt (; ) is an aphanite, aphanitic (fine-grained) extrusive igneous rock formed from the rapid cooling of low-viscosity lava rich in magnesium and iron (mafic lava) exposed at or very near the planetary surface, surface of a terrestrial ...

pillow lava. The basement rocks are divided into a number of

terrane In geology, a terrane (; in full, a tectonostratigraphic terrane) is a crust fragment formed on a tectonic plate (or broken off from it) and accreted or " sutured" to crust lying on another plate. The crustal block or fragment preserves its own ...

s, that are believed to have been combined together by subduction or strike-slip processes, by mid Cretaceous times (100 Ma). Murihiku Terrane rocks lies beneath the Northland Region on the western side, but do not crop out. The Murihiku Terrane was formed in Late

Triassic The Triassic ( ) is a geologic period and system which spans 50.6 million years from the end of the Permian Period 251.902 million years ago ( Mya), to the beginning of the Jurassic Period 201.36 Mya. The Triassic is the first and shortest period ...

to Late

Jurassic The Jurassic ( ) is a Geological period, geologic period and System (stratigraphy), stratigraphic system that spanned from the end of the Triassic Period million years ago (Mya) to the beginning of the Cretaceous Period, approximately Mya. The J ...

times (220–145 Ma). A line of

Dun Mountain-Maitai Terrane The Dun Mountain-Maitai Terrane comprises the Dun Mountain Ophiolite Belt (also called the Mineral Belt), Maitai Group and Patuki Mélange. The Dun Mountain Ophiolite is an ophiolite of Permian age located in New Zealand's South Island. Prehistori ...

rocks pass NNW-SSE through the centre of the Northland Region, separating the Murihiku Terrane from the more easterly terranes, and produce a detectable Junction Magnetic Anomaly (JMA), but do not crop out. Caples Terrane rocks crop out to form the Waipapa Horst (Omahuta and Puketi forest area). The Caples Terrane was formed in

Permian The Permian ( ) is a geologic period and stratigraphic system which spans 47 million years from the end of the Carboniferous Period million years ago (Mya), to the beginning of the Triassic Period 251.9 Mya. It is the last period of the Paleoz ...

to Triassic times (300–200 Ma). Hunua Terrane rocks (part of the Waipapa Composite Terrane) crop out throughout much of eastern Northland, south of Whangaroa. The rocks are generally fine grained and highly deformed. The Hunua Terrane was formed in Triassic to Jurassic times (250–145 Ma). Mount Camel Terrane rocks crop out near Mount Camel and the Karikari Peninsula. They were formed in the early

Cretaceous The Cretaceous ( ) is a geological period that lasted from about 145 to 66 million years ago (Mya). It is the third and final period of the Mesozoic Era, as well as the longest. At around 79 million years, it is the longest geological period of th ...

(131–104 Ma).

Te Kuiti group coal and limestone

The Te Kuiti Group Rocks overlie the basement rocks, and are present in Northland,

Auckland Auckland (pronounced ) ( mi, Tāmaki Makaurau) is a large metropolitan city in the North Island of New Zealand. The List of New Zealand urban areas by population, most populous urban area in the country and the List of cities in Oceania by po ...

, the Waikato, and

King Country The King Country (Māori: ''Te Rohe Pōtae'' or ''Rohe Pōtae o Maniapoto'') is a region of the western North Island of New Zealand. It extends approximately from the Kawhia Harbour and the town of Otorohanga in the north to the upper reaches of ...

, although they have often been eroded or covered. Rocks containing coal were formed from swampland in Late Eocene times (37–34 Ma). The land sank, the sea transgressed, and calcareous sandstone,

mudstone Mudstone, a type of mudrock, is a fine-grained sedimentary rock whose original constituents were clays or muds. Mudstone is distinguished from '' shale'' by its lack of fissility (parallel layering).Blatt, H., and R.J. Tracy, 1996, ''Petrology. ...

, and

limestone Limestone ( calcium carbonate ) is a type of carbonate sedimentary rock which is the main source of the material lime. It is composed mostly of the minerals calcite and aragonite, which are different crystal forms of . Limestone forms whe ...

were deposited in Oligocene times (34–24 Ma). Eocene coal measures crop out in the east, between

Kerikeri Kerikeri () is the largest town in Northland, New Zealand. It is a tourist destination north of Auckland and north of the northern region's largest city, Whangarei. It is sometimes called the Cradle of the Nation, as it was the site of th ...

and

Waipu Waipu may refer to: New Zealand *Waipu Lagoons, near New Plymouth *Waipu, New Zealand, town in Northland *Waipu River, river in Northland Taiwan *Waipu District, Taichung *Waipu Fishing Port The Waipu Fishing Port () is a fishing port in Houl ...

. Coal has been mined around

Kamo The name Kamo may refer to the following: Places Japan (Note: ''kamo'' ( 鴨), is the common word for ''duck'' in Japanese, but the following names do not necessarily mean ''duck'' and are not necessarily written with that character.) *Kamo, Nii ...

, north of Whangarei.Claudia Orange
Northland places – Kamo
Te Ara – the Encyclopedia of New Zealand. Updated 20 November 2009. Retrieved 3 June 2010. Limestone crops out around Whangarei, with an interesting display at the Waro Rocks Scenic Reserve, north of Hikurangi.

Northland Allochthon

In Early Miocene times (24–21 Ma), a series of thrust sheets was emplaced over Northland,Spörli, K.B. and Hayward, B.W. (2002)
Geological overview of Northland
pp. 3–10 in Smith, V. and Grenfell, H.R. (editors) (2002): Fieldtrip Guides, Geological Society of New Zealand Annual Conference “Northland 2002”, Geological Society of NZ Miscellaneous Publication 112B, 116 pp. . Accessed 23 May 2010. extending as far south as the Kaipara Harbour and Albany areas. The rocks came from the northeast (perhaps beyond the Vening Meinesz Fracture Zone), and were emplaced in reverse order, but the right way up. The original rocks are of Cretaceous to Oligocene age (90–25 Ma), and include mudstone, limestone and basalt

lava Lava is molten or partially molten rock (magma) that has been expelled from the interior of a terrestrial planet (such as Earth) or a moon onto its surface. Lava may be erupted at a volcano or through a fracture in the crust, on land or un ...

. These rocks outcrop around Silverdale, Warkworth, and Wellsford, reaching as far south as Albany. The

allochthon upright=1.6, Schematic overview of a thrust system. The hanging wall block is (when it has reasonable proportions) called a nappe. If an erosional hole is created in the nappe that is called a window (geology)">window. A klippe is a solitary out ...

includes displaced Te Kuiti group rocks. The basalt lava of the Tangihua Complex is believed to represent sea floor, that has been obducted onto Northland to form high standing massifs, such as the Reinga, Ahipara, Warawara, Mangakahia, and Maungataniwha massifs. Isolated bodies of serpentine occur at North Cape, and south of Maungaturoto. The Northland and East Cape Allochthons are assumed to constitute part of a single

, that have later separated, due to the clockwise rotation of the eastern part of the North Island, relative to the western part.

Early Miocene volcanism

A subduction-related volcanic belt became active to the west of the current land in Northland in Miocene times (23 Ma), and gradually moved south down to

Taranaki Taranaki is a region in the west of New Zealand's North Island. It is named after its main geographical feature, the stratovolcano of Mount Taranaki, also known as Mount Egmont. The main centre is the city of New Plymouth. The New Plymouth Dist ...

. It produced mainly andesitic

stratovolcano A stratovolcano, also known as a composite volcano, is a conical volcano built up by many layers (strata) of hardened lava and tephra. Unlike shield volcanoes, stratovolcanoes are characterized by a steep profile with a summit crater and per ...

es. Most of these volcanoes have been eroded, but remnants form the Waipoua Plateau (basaltic, 19–18 Ma), and Waitākere Ranges (andesitic, 22–16 Ma). An eastern volcanic belt formed mainly andesitic volcanoes around Karikari (22.3–19.8 Ma), Whangaroa (20.5–17.5 Ma), Whangarei Heads (21.5–16.1 Ma), Bream Head, and created the Hen and Chicken Islands (19.5–16.5 Ma).

Waitemata sandstone

Miocene volcanoes and the Northland Allochthon eroded to form the Waitemata sandstone, between Whangarei and Auckland, on the eastern side of Northland.Edbrooke, S.W. (compiler) (2001). ''Geology of the Auckland Area''. Lower Hutt: GNS Science. .

Uplift

By middle Miocene, Northland was uplifted above sea level, with a slight westward tilt, exposing basement rocks on the eastern side, and resulting in a tendency for rivers to flow in a westerly direction.

Recent basaltic volcanism

Intra-plate basaltic volcanism has occurred in Northland from late Miocene to

Quaternary The Quaternary ( ) is the current and most recent of the three periods of the Cenozoic Era in the geologic time scale of the International Commission on Stratigraphy (ICS). It follows the Neogene Period and spans from 2.58 million years ...

times. The Kerikeri volcanic group covered the area from Kaikohe, Kerikeri, to Whangarei. Activity began about 9 Ma, and the youngest cones are probably only tens of thousands of years old. Little Barrier Island is the emergent part of a large dacitic-rhyodacitic stratovolcano, formed through two eruptive periods (3 Ma, and 1.6–1.2 Ma).Edbrooke, S.W. (compiler) (2001). ''Geology of the Auckland Area'', p. 39. Lower Hutt: GNS Science. .

Coastal dunes

The coastal barriers north and south of the entry to the Kaipara Harbour, are essentially consolidated sand dunes, built up over the last few million years. Similar dunes have formed in the north from

Ahipara Ahipara is a town and locality in Northland, New Zealand at the southern end of Ninety Mile Beach, with the Tauroa Peninsula to the west and Herekino Forest to the east. Ahipara Bay is to the north west. Kaitaia is 14 km to the north east, ...

Cape Reinga , type =Cape , photo = Cape Reinga, Northland, New Zealand, October 2007.jpg , photo_width = 270px , photo_alt = , photo_caption = , map = New Zealand , map_width = 270px ...

, connecting what used to be isolated islands to the rest of the North Island, thus creating a large tombolo.Black, Philippa and Gregory, Murray (2002)
Field trip 9: Geological gems of the Far North
in Smith, V. and Grenfell, H.R. (editors) (2002): Fieldtrip Guides, Geological Society of New Zealand Annual Conference “Northland 2002”, Geological Society of NZ Miscellaneous Publication 112B, 116 pp. . Accessed 23 May 2010. Sand on the eastern coast tends to be more pure quartz, and appears white.

Geothermal areas

Hot springs exist at

Ngawha Springs Ngawha Springs ( mi, Ngāwhā) is a small settlement and hot water springs approximately five kilometres east of the town of Kaikohe in Northland, New Zealand. ''Ngāwhā'' means "boiling spring". The springs reputedly have therapeutic, balne ...

, with temperatures around 40–50 °C. There are also hot springs at Waiwera and

Parakai Parakai is a town in the North Island of New Zealand, sited 43 kilometres (27 miles) northwest of Auckland, close to the southern extremity of the Kaipara Harbour. Helensville is about 3 km (2 miles) to the south-east, and Waione ...

, in the southern part of the

Northland Peninsula The Northland Peninsula, called the North Auckland Peninsula in earlier times, is in the far north of the North Island of New Zealand. It is joined to the rest of the island by the Auckland isthmus, a narrow piece of land between the Waitematā H ...

, in the

Auckland Region Auckland () is one of the sixteen regions of New Zealand, which takes its name from the eponymous urban area. The region encompasses the Auckland Metropolitan Area, smaller towns, rural areas, and the islands of the Hauraki Gulf. Containing ...

. All are used for hot pools. The Ngawha geothermal field is also used for the generation of electricity.

Geological resources

Copper has been mined at Kaeo, silver, gold and mercury at Puhipuhi, and antimony at Russell. Coal has been mined at Kawakawa, Hikurangi, Kamo and

Kiripaka Kiripaka is a locality in Northland, New Zealand. The settlement of Glenbervie lies to the southwest, and Ngunguru is to the northeast. "Kiripaka" means flint, schist or asbestos in the Māori language. Demographics Kiripaka statistical area ...

. The Northland Basin, to the west of the Northland Peninsula is considered as having potential for oil and

gas Gas is one of the four fundamental states of matter (the others being solid, liquid, and plasma). A pure gas may be made up of individual atoms (e.g. a noble gas like neon), elemental molecules made from one type of atom (e.g. oxygen), or ...

. Halloysite clay is mined at Matauri Bay and Mahimahi. High quality

quartz Quartz is a hard, crystalline mineral composed of silica (silicon dioxide). The atoms are linked in a continuous framework of SiO4 silicon-oxygen tetrahedra, with each oxygen being shared between two tetrahedra, giving an overall chemical form ...

sand is dredged from near Parengarenga Harbour.

Geological hazards

The main geological hazard in Northland is the potential for landslides, particularly in mudstones and sandstones of the Northland Allochthon. Northland has the least incidence of earthquakes of anywhere in New Zealand. Volcanic activity is dormant rather than extinct. However,

tsunami A tsunami ( ; from ja, 津波, lit=harbour wave, ) is a series of waves in a water body caused by the displacement of a large volume of water, generally in an ocean or a large lake. Earthquakes, volcanic eruptions and other underwater explo ...

s generated by

earthquake An earthquake (also known as a quake, tremor or temblor) is the shaking of the surface of the Earth resulting from a sudden release of energy in the Earth's lithosphere that creates seismic waves. Earthquakes can range in intensity, from ...

s around the Pacific can occur on the east coast.

Geological sites of interest

Hunua Terrane can be seen along much of the coast between the Bay of Islands and Whangarei. Mount Camel Terrane can be seen at Parerake Bay, Karikari Peninsula. Kamo coal measures can be seen near Kamo. Whangarei Limestone can be seen at Waro Rocks Scenic Reserve, north of Hikurangi. Many of the hills in Northland are formed from the Tangihua Complex rocks of the Northland Allochthon. Maungaraho, north of Tokatoka, gives a good example of a remnant of an early Miocene andesitic volcano. Whangarei Heads represents another example. Sand dunes can be seen on either side of the coast between Kaitaia and Cape Reinga.

Maps

Geological maps of New Zealand are now freely accessible on line from the New Zealand Institute of Geological and Nuclear Science (GNS Science), a New Zealand Government Research Institute. Geological Maps of New Zealand from Institute of Geological and Nuclear Sciences (GNS Science)
- a New Zealand government Crown Research Institute. There is also a 1 : 25 000 map of the Whangarei Urban Area, published in 2003.