The Raukumara Region of New Zealand corresponds to the East Cape of the North Island, and associated mountain ranges.
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 east of the North Island, and causing the North Island Fault System, and a series of SSW-NNE trending basins and ranges, including the Raukumara Range. Successively newer rocks have been accreted to the east coast.
The Raukumara Region used to be adjacent to Northland, before being shifted to its current position, and many rocks of the two regions match.
To the north of the Raukumara Range lies the Bay of Plenty, formed of Torlesse (Waioeka) Greywacke. The central ranges are covered by in-place and allochthonous (displaced) Cretaceous to Oligocene rocks. To the south are more recent, mainly Miocene and Pliocene, rocks.
All basement rocks beneath the Raukumara Region belong to the Torlesse Composite (Waioeka) Terrane, of late Jurassic to early Cretaceous age (150-100 Ma). They are largely composed of Greywacke (hardened sandstone and mudstone), that accumulated in a deep marine environment. These rocks are exposed to the north of the Raukumara Range, from Whakatāne to Papatea Bay.
Sandstones and mudstones were deposited over the region in Cretaceous to Oligocene times (100-24 Ma). These rocks still cover the Raukumara Range.
In Early Miocene times (24-21 Ma), when the Raukumara region was still adjacent to Northland, a series of thrust sheets was emplaced over much of the East Cape area. Large portions of the Cretaceous to Oligocene rocks have been displaced by tens to hundreds of kilometres, forming what is known as the East Cape Allochthon. The rocks came from the Northeast, and were emplaced in reverse order, but the right way up. The original rocks are of Cretaceous to Oligocene age (100-24 Ma), and include mudstones, limestone and basalt lava.
Most of the rocks east of the line from Papatea Bay to Waipiro Bay, and rocks just north of Whatatutu are allochthonous. Allochthonous rocks are assumed to underlie the more recent rocks to the south as well.
In the north, from Cape Runaway to Tokata, are allochthonous basaltic rocks, believed to represent sea floor, that has been obducted onto the land. These rocks correspond to the Tangihua rocks of Northland.
During Miocene and Pliocene times, sandstone, mudstone, and some limestone was deposited over much of the southern area of the Raukumara region.
Marine terraces are common between Ōpōtiki and East Cape, and at Māhia Peninsula.
Sinter deposits occur around the Te Puia Springs.
The area to the south of the Raukumara region contains oil seeps (Waimata Valley and Waitangi Station), and is believed to have potential commercial gas and oil reserves. While the region has been explored, and minor reserves found, no major commercial reserves have yet been found.
The Raukumara Region, and the Hikurangi Trough are prone to earthquakes, with the consequential risk of tsunami. For example, a magnitude 6.8 earthquake hit the Gisborne area on 20 December 2007. [1] There were also two major tsunamis on 26 March 1947 and 17 May 1947. [2]
Much of the land is composed of soft mudstones, that are easily eroded, particularly in areas without bush cover.
The region is also prone to flooding, when tropical cyclones manage to come sufficiently far south.
The region can also receive minor falls of volcanic ash from the Taupo Volcanic Zone.
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. [4]
The main maps are the 1 : 250 000 QMap series, which was completed as a series of 21 maps in 2010. Low resolution versions of these maps (without the associated booklet) can be downloaded from the GNS site. [5] The map for the Raukumara Area was published in 2001. [6]
Alternatively digital GIS layers are available using the free GNS map viewer.
The Raukūmara Range runs from the north-eastern end of the Huiarau Range north-eastward to Wharekahika / Hicks Bay, between Cape Runaway and East Cape, at the northern end of the Gisborne District, on the North Island of New Zealand. It is the north-northeastern end segment of the North Island's main mountain chain, which runs from Wellington in the south to the Gisborne District. The western side of the range is in the Ōpōtiki District of the eastern Bay of Plenty and the eastern side in the East Coast region of the Gisborne District. State Highway 2 runs between the Raukūmara Range and the Huiarau Range on its route between the town of Ōpōtiki and the city of Gisborne.
The Moehau Range is the northernmost range on the Coromandel Peninsula, extending from the settlement of Colville, New Zealand northwards to the tip of the peninsula. Mount Moehau is the highest point of the range, at 892m above sea level.
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 geology of Tasmania is complex, with the world's biggest exposure of diabase, or dolerite. The rock record contains representatives of each period of the Neoproterozoic, Paleozoic, Mesozoic and Cenozoic eras. It is one of the few southern hemisphere areas that were glaciated during the Pleistocene with glacial landforms in the higher parts. The west coast region hosts significant mineralisation and numerous active and historic mines.
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 Taupō Volcanic Zone. Large amounts of pumice from the Taupō 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.
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.
The Tahora Formation is a Late Cretaceous geologic formation that outcrops in northeastern New Zealand near Napier. It is Haumurian in age according to the New Zealand geologic time scale. It forms part of the Upper Cretaceous to Teurian (Danian) Tinui Group. It unconformably overlies the Jurassic to Lower Cretaceous Urewera Group or the Upper Cretaceous Matawai Group. It is conformably overlain by the Haumurian to Teurian Whangai Formation. It consist of three members, the Maungataniwha Sandstone Member, the Mutuera Member and the Houpapa Member. It is named for Tahora Station, south of Matawai in the Gisborne Region. The aptly named Maungataniwha Sandstone Member is known for its rich reptile fossil remains, first investigated by amateur palaeontologist Joan Wiffen.
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 Whangārei, and Oligocene limestone crops out at Hikurangi, near Whangārei.
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, the main fault forming the boundary between the Pacific Plate and the Indo-Australian Plate, that generated the Southern Alps.
The Atacama Fault Zone (AFZ) is an extensive system of faults cutting across the Chilean Coastal Cordillera in Northern Chile between the Andean Mountain range and the Pacific Ocean. The fault system is north–south striking and runs for more than 1100 km North and up to 50 km in width through the Andean forearc region. The zone is a direct result of the ongoing subduction of the Eastward moving Nazca plate beneath the South American plate and is believed to have formed in the Early Jurassic during the beginnings of the Andean orogeny. The zone can be split into 3 regions: the North, Central and South.
The Taranaki Basin is an onshore-offshore Cretaceous rift basin on the West Coast of New Zealand. Development of rifting was the result of extensional stresses during the breakup of Gondwanaland. The basin later underwent fore-arc and intra-arc basin development, due to the subduction of the Pacific Plate under the Australian Plate at the Hikurangi Subduction System. The basin covers approximately 100,000 km2 of which the majority is offshore. The basin contains mostly marine sediment, with significant terrestrial sediment from the Late Cretaceous to the Eocene. The majority of New Zealand's oil and gas production occurs within the basin, with over 600 wells and approximately 20 oil and gas fields being drilled.
The Halibut Field is an oil field, within the Gippsland Basin offshore of the Australian state of Victoria. The oil field is located approximately 64 km offshore of southeastern Australia. The total area of this field is 26.9 km2 and is composed of 10 mappable units.
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 Waitemata Group is an Early Miocene geologic group that is exposed in and around the Auckland Region of New Zealand, between the Whangarei Harbour in the North and the Raglan Harbour in the South. The Group is predominantly composed of deep water sandstone and mudstone (flysch). The sandstone dominated units form the cliffs around the Waitemata Harbour and rare more resistant conglomerates underlie some of Auckland's prominent ridges.
Ōpōtiki District is a territorial authority district in the eastern Bay of Plenty Region on the North Island of New Zealand. It stretches from Kutarere and the eastern shore of Ōhiwa Harbour in the west to Cape Runaway in the north-east, and south from Ōpōtiki town up the Waioeka River into the Raukumara Range. Ōpōtiki District Council is headquartered in Ōpōtiki, the largest town.
The Whangārei volcanic field is an area of intra-plate monogenetic volcanism located near the city of Whangārei, North Island, New Zealand. It was last active between 260,000 to 319,000 years ago and continues to be potentially active as a low-velocity seismic zone in the crust exists beneath Whangārei, which is interpreted to be a body of partial melt. This mantle source has been coupled to the lithosphere for about 8 million years. As the field has potentially been active at low frequency for millions of years, with 100,000 years or more between events it might best be regarded as dormant. The recent vents active in the last million years include some dacite in composition. Composition details are freely available for most of the field but many vents do not have ages.