Geology of the Northland Region
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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 volcanic rocks that can be seen in fields across Northland are from the Great Taupo eruption.
A subduction zone is believed to have existed to the northeast of Northland in early Miocene times, causing the Northland Allochthon to thrust over much of the peninsula and volcanic belts 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 dunes 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.
- 1 Basement rocks
- 2 Te Kuiti group coal and limestone
- 3 The Northland Allochthon
- 4 Early Miocene volcanism
- 5 Waitemata sandstone
- 6 Uplift
- 7 Recent basaltic volcanism
- 8 Coastal dunes
- 9 Geothermal areas
- 10 Geological resources
- 11 Geological hazards
- 12 Geological sites of interest
- 13 Maps
- 14 See also
- 15 References
- 16 Further reading
As with most of New Zealand, the basement rocks of the Northland Region are mainly composed of greywacke (indurated sandstone), argillite, and chert, together with volcanic rocks, such as basalt pillow lava. The basement rocks are divided into a number of terranes, that are believed to have been combined together by subduction or strike-slip processes, by mid Cretaceous times (100 Ma).
A line of Dun Mountain-Maitai Terrane 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 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 (131–104 Ma).
Te Kuiti group coal and limestone
The Te Kuiti Group Rocks overlie the basement rocks, and are present in Northland, Auckland, the Waikato, and King Country, 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, and limestone were deposited in Oligocene times (34–24 Ma).
Limestone crops out around Whangarei, with an interesting display at the Waro Rocks Scenic Reserve, north of Hikurangi.
The Northland Allochthon
In Early Miocene times (24–21 Ma), a series of thrust sheets was emplaced over Northland, 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. The allochthon 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 allochthon, 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. It produced mainly andesitic stratovolcanoes. Most of these volcanoes have been eroded, but remnants form the Waipoua Plateau (basaltic, 19–18 Ma), and Waitakere 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).
Miocene volcanoes and the Northland Allochthon eroded to form the Waitemata sandstone, between Whangarei and Auckland, on the eastern side of Northland.
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 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.
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 to Cape Reinga, connecting what used to be isolated islands to the rest of the North Island, thus creating a large tombolo. Sand on the eastern coast tends to be more pure quartz, and appears white.
Hot springs exist at Ngawha Springs, with temperatures around 40–50 °C. There are also hot springs at Waiwera and Parakai, in the southern part of the Northland Peninsula, in the Auckland Region. All are used for hot pools. The Ngawha geothermal field is also used for the generation of electricity.
Copper has been mined at Kaeo, silver, gold and mercury at Puhipuhi, and antimony at Russell.
High quality quartz sand is dredged from near Parengarenga Harbour.
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. However, tsunamis generated by earthquakes 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.
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.
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. The map for the Kaitaia Area was published in 1996. The map for the Whangarei Area was published in 2009. The map for the Auckland Area was published in 2002.
There is also a 1 : 25 000 map of the Whangarei Urban Area, published in 2003.
- Adams, C.J.; Campbell H.J.; Graham I.J.; Mortimer N. (1998). "Torlesse, Waipapa and Caples suspect terranes of New Zealand: Integrated studies of their geological history in relation to neighbouring terranes" (PDF). Episodes. 21 (4): 235–240. Retrieved 31 May 2010.
- 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. ISBN 0-908678-90-8. Accessed 23 May 2010.
- Claudia Orange. Northland places – Kamo, Te Ara – the Encyclopedia of New Zealand. Updated 20 November 2009. Retrieved 3 June 2010.
- Spörli, K.B. (2007). "A stratigraphic unit converted to fault rocks in the Northland Allochthon of New Zealand: Response of a siliceous claystone to obduction". Whence the mountains?: inquiries into the evolution of orogenic systems : a volume in honor of Raymond A. Price. Special Paper. 433 (Proce R.A., Sears J.W. Harms T.A. & Evenchick C.A. ed.). Geological Society of America. pp. 331–348. Retrieved 31 May 2010.
- Edbrooke, S.W. (compiler) (2001). Geology of the Auckland Area. Lower Hutt: GNS Science. ISBN 0-478-09714-X.
- Davy, Bryan (2008). Marine seismic reflection profiles from the Waitemata-Whangaparaoa region, Auckland, New Zealand Journal of Geology and Geophysics, 51 (3), 161–173.
- Edbrooke, S.W. (compiler) (2001). Geology of the Auckland Area, p. 39. Lower Hutt: GNS Science. ISBN 0-478-09714-X.
- 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. ISBN 0-908678-90-8. Accessed 23 May 2010.
- Gregory, M.R.; Martin, A.J.; and Campbell, K.A. (2004). Compound trace fossils formed by plant and animal interactions: Quaternary of northern New Zealand and Sapelo Island, Georgia (USA), Fossils and Strata 51, 88–105.
- "Ngawha generator secured in local ownership". Scoop.
- Claudia Orange. Northland places – Hikurangi coal mine, Te Ara – the Encyclopedia of New Zealand. Updated 20 November 2009. Retrieved 3 June 2010.
- Case study: Halloysite clay, New Zealand Minerals Industry Association
- Emily Lane; Roy Walters; Jade Arnold; Helen Roulston. Northland Regional Council Tsunami Modelling Study 1, NIWA Client Report: CHC2007-109, September 2007.
- New Zealand Institute of Geological and Nuclear Sciences (GNS Science) – a New Zealand government Crown Research Institute.
- GNS Map of New Zealand's Geological Foundations
- GNS New Zealand Geological Maps.
- Geology of the Kaitaia Area, Isaac, M.J., GNS Science, 1996. (1 : 250 000 map).
- Geology of the Whangarei Area, Edbrooke, S.W., Brook, F.J., GNS Science, 2009. (1 : 250 000 map).
- Geology of the Auckland Area, Edbrooke, S.W., GNS Science, 2002. (1 : 250 000 map).
- Geology of the Whangarei Urban Area, White, P.J., Perrin, N.D., GNS Science, 2003. (1 : 25 000 map of the Whangarei Urban Area)
- 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 978-1-877480-00-3
- Christie, A. B. and Barker, R. G. (2007). Mineral resource assessment of the Northland Region, New Zealand. GNS Science science report 2007/06, May 2007.