Ontong Java Plateau

The Ontong Java Plateau (OJP) is a huge oceanic plateau located in the southwestern Pacific Ocean, north of the Solomon Islands. The OJP was emplaced around 120 million years ago (Ma) with a much smaller volcanic event around 90 Ma. Two other southwestern Pacific plateaus, Manihiki and Hikurangi, now separated from the OJP by Cretaceous ocean basins, are of similar age and composition and probably formed as a single plateau and a contiguous large igneous province together with the OJP.[1] When emplaced this Ontong Java–Manihiki–Hikurangi plateau covered 1% of Earth's surface and represented a volume of 80 million km3 (19 million cu mi) of basaltic magma.[2] This "Ontong Java event", first proposed in 1991, represents the largest volcanic event of the past 200 million years, with a magma emplacement rate estimated at up to 22 km3 (5.3 cu mi) per year over 3 million years, several times larger than the Deccan Traps.[3] The smooth surface of the OJP is punctuated by seamounts such as the Ontong Java Atoll, the largest atoll in the world.[4]

Ontong Java Plateau is located in Pacific Ocean
Ontong Java Plateau
Ontong Java Plateau
Location of the Ontong Java Plateau in the Pacific Ocean

Geological setting

The OJP covers 1.5 million km2 (580,000 sq mi), roughly the size of Alaska. It reaches up to 1,700 m (5,600 ft) below sea level but has an average depth closer to 2,000–3,000 m (6,600–9,800 ft). It is bounded by Lyra Basin to the northwest, East Mariana Basin to the north, Nauru Basin to the northeast, and the Ellice Basin to the southeast. The OJP has collided with the Solomon Islands island arc and now lies on the inactive Vitiaz Trench and the PacificAustralian plate boundary.[4]

The high plateau, with a crustal thickness estimated to at least 25 km (16 mi) but probably closer to 36 km (22 mi), has a volume of more than 5 million km3 (1.2 million cu mi). The maximum extent of the event can, however, be much larger since lavas in several surrounding basins are closely related to the OJP event and probably represent dike swarms associated with the emplacement of the OJP.[4]

Tectonic evolution

OJP formed quickly over a mantle plume head, most likely the then newly formed Louisville hotspot, followed by limited volcanism for at least 30 million years. The extant seamounts of the Louisville Ridge started to form 70 Ma and have a different isotopic composition, and therefore a shift in intensity and magma supply in the plume must have occurred before that.[5]

The early, short-duration eruptions of OJP coincide with the global Early Aptian oceanic anoxic event (known as OAE1a or the Selli Event, 125.0–124.6 Ma) that lead to the deposition of black shales during the interval 124–122 Ma. Additionally, isotopic records of seawater in sediments have been associated with the 90 Ma OJP submarine eruptions.[6]

About 80% of the OJP is being subducted beneath the Solomon Islands. Only the uppermost 7 km (4.3 mi) of the crust is preserved on the Australian Plate.[7] This collision has lifted some of the OJP between 200 and 2,000 m (660–6,560 ft) above sea level. The construction of Pliocene stratovolcanoes in the western end of the convergence zone has resulted in the New Georgia Islands (1,768 m, 5,801 ft) and Bougainville Island (2,743 m, 8,999 ft). Shortening, uplift, and erosion of the northern Melanesian arc and the Malaita accretionary prism at deep levels has produced Guadacanal (2,447 m, 8,028 ft), Makira (1,250 m, 4,100 ft), and Malaita (1,251 m, 4,104 ft).[8]

References

Notes

  1. ^ Taylor 2006, Abstract
  2. ^ Rizo 2016
  3. ^ Tarduno et al. 1991, p. 401
  4. ^ a b c Neal et al. 1993, Physical features and gross structure of the OJP, pp. 184–187
  5. ^ Mahoney et al. 1993, Abstract
  6. ^ Tejada et al. 2009, Abstract; Introduction, pp. 855–856
  7. ^ Mann & Taira 2004, Abstract
  8. ^ Mann & Taira 2004, Erosional levels of rocks in the Solomon Islands, p. 166

Sources

Further reading

Coordinates: 3°03′S 160°23′E / 3.050°S 160.383°E

Broken Ridge

Broken Ridge or Broken Plateau is an oceanic plateau in the south-eastern Indian Ocean. Broken Ridge once formed a large igneous province (LIP) together with the Kerguelen Plateau. When Australia and Antarctica started to separate, Broken Ridge and the Kerguelen Plateau got separated by the Southeast Indian Ridge. Alkalic basalt from Broken Ridge has been dated to 95 Ma.Broken Ridge stretches 1,200 km (750 mi) from the southern end of Ninety East Ridge towards the south-western corner of Australia. It is up to 400 km (250 mi) wide and reaches 1,000 m (3,300 ft) below sea level. It is separated from the Diamantina Fracture Zone on its southern side by a 3,000 m (9,800 ft) escarpment, while on the northern side the ridge slopes gently towards the abyssal Wharton Basin. The sediment cover on the ridge reaches 800 m (2,600 ft) and the Moho is found at about 20 km (12 mi). It is separated from the Naturaliste Plateau by the Dirck Hartog Ridge.

The Kerguelen LIP covered 2.3×10^6 km2 (0.89×10^6 sq mi) making it the second largest LIP on Earth (after the Ontong Java Plateau in the Pacific). Both these enormous LIPs reaches 2–4 km (1.2–2.5 mi) above the surrounding ocean floor and have a crustal thickness of 20–40 km (12–25 mi) (compared to oceanic crust typically around 7 km (4.3 mi) thick.)

The Broken Ridge and Kerguelen Plateau are now separated by 1,800 km (1,100 mi). When they broke-up, the southern flank of Broken Ridge was uplifted some 2,000 m (6,600 ft) and reached above sea level.The Kerguelen LIP has a long and complicated history, however, and is probably the least "typical" of all LIPs.

Rocks from both the Broken Ridge and the Kerguelen Plateau contain a continental component or "fingerprint". In the Early Cretaceous, the Kerguelen hotspot was split into several diapirs of various sizes, composition, and ascent rates. These separate diapirs created the Bunbury Basalt, the Southern Kerguelen Plateau, the Rajmahal Traps/Indian lamprophyres, Antarctic lamprophyres, and the Central Kerguelen Plateau/Broken Ridge. In the late Cretaceous, activity in the mantle slowed and the Kerguelen hotspot was reduced to a single plume which created the Ninety East Ridge.

120-95 Ma when the Southern and Central Kerguelen Plateau formed together with the Broken Ridge, the Kerguelen hotspot produced 1 km3 (0.24 cu mi)/year, but 95-25 Ma the output decreased to 0.1 km3 (0.024 cu mi).

Carteret Islands

The Carteret Islands (also known as Carteret Atoll, Tulun or Kilinailau Islands/Atoll) are Papua New Guinea islands located 86 km (53 mi) north-east of Bougainville in the South Pacific. The atoll has a scattering of low-lying islands called Han, Jangain, Yesila, Yolasa and Piul, in a horseshoe shape stretching 30 km (19 mi) in north-south direction, with a total land area of 0.6 square kilometres (0.2 sq mi) and a maximum elevation of 1.5 metres (4 ft 11.1 in) above sea level.

The group is made up of islands collectively named after the British navigator Philip Carteret, who was the first European to discover them, arriving in the sloop Swallow in 1767.As of 2005, about one thousand people live on the islands. Han is the most significant island, with the others being small islets around the lagoon. The main settlement is at Weteili on Han. The island is near the edge of the large geologic formation called the Ontong Java Plateau.

Darwin Rise

The Darwin Rise is broad triangular region in the north central Pacific Ocean where there is a concentration of atolls.

During his voyage across the globe Charles Darwin realised that vertical crustal motion must be responsible for the formation of continents and ocean basins, as well as isolated atolls in the Pacific. He deduced that the central basin of the Pacific had subsided while surrounding areas had risen. In 1964 U.S. geologist Henry Menard subsequently named the uplifted area in the Pacific after the English naturalist.

Early Cretaceous

The Early Cretaceous (geochronological name) or the Lower Cretaceous (chronostratigraphic name), is the earlier or lower of the two major divisions of the Cretaceous. It is usually considered to stretch from 146 Ma to 100 Ma.

Flood basalt

A flood basalt is the result of a giant volcanic eruption or series of eruptions that covers large stretches of land or the ocean floor with basalt lava. Flood basalt provinces such as the Deccan Traps of India are often called traps, after the Swedish word trappa (meaning "stairs"), due to the characteristic stairstep geomorphology of many associated landscapes. Michael R. Rampino and Richard Stothers (1988) cited eleven distinct flood basalt episodes occurring in the past 250 million years, creating large volcanic provinces, lava plateaus, and mountain ranges. However, more have been recognized such as the large Ontong Java Plateau, and the Chilcotin Group, though the latter may be linked to the Columbia River Basalt Group. Large igneous provinces have been connected to five mass extinction events, and may be associated with bolide impacts.

Large igneous province

A large igneous province (LIP) is an extremely large accumulation of igneous rocks, including intrusive (sills, dikes) and extrusive (lava flows, tephra deposits), arising when magma travels through the crust towards the surface. The formation of LIPs is variously attributed to mantle plumes or to processes associated with divergent plate tectonics. The formation of some of the LIPs the past 500 million years coincide in time with mass extinctions and rapid climatic changes, which has led to numerous hypotheses about the causal relationships. LIPs are fundamentally different from any other currently active volcanoes or volcanic systems.

Lihir Island

Lihir Island (a.k.a. Niolam Island) is the largest island in the Lihir group of islands, 22 km long and 14.5 km wide, in Papua New Guinea's New Ireland Province. It consists of a complex of several overlapping basaltic stratovolcanoes rising 700 m above sea level. While the volcanoes are not currently active, geothermal activity is still present. The island is in what was the forearc basin associated with the subduction of the Pacific Plate beneath the North Bismarck Plate. Subduction stopped about 10 million years ago with the collision of the Ontong Java plateau with the subduction zone.The island is located 900 km (560 mi) NE of Port Moresby. Annual rainfall averages 4,800 mm (190 in); temperature ranges between 19 and 35 degrees Celsius. The population of the Lihir Group increased from 12,570 in 2000 to an estimated 18,000 in 2007. Residents are of Melanesian descent and have predominantly a subsistence lifestyle.

Lihirians follow traditional belief systems, although official census records indicate that 99% of the PNG population are Christians, with Catholicism being the largest denomination. Most villages are located on the coastal fringe, although it is thought that originally some villages were located inland but were moved to the coast at the encouragement of missionaries.

The economic focal point of the island is the Ladolam Gold Mine. Ladolam represents one of the largest epithermal gold deposits in the world and it is hosted by high-potassic igneous rocks. The mine is operated by Newcrest Mining Limited. The mine holds one of the world's largest gold resources (46 million ounces). Grab samples from the submarine Conical Seamount, located about 8 km south of Lihir Island, contain high gold concentrations of up to 230 g/t Au (avg. 26 g/t, n=40) that are hosted by high-potassic trachybasalts.The mine is located on a geothermically active area and to enable the mine to proceed, steam relief wells have been drilled to release subterranean pressure. The steam has, in part, been captured and is used to operate a 50 MW geothermal power station which generates approximately 25% of the mine's power requirements. Mine tailings are discharged into the sea.

The largest settlement on the Island is Londolovit, where most of the expatriate mine employees live. Basic shopping and health care facilities are located there. The local hospital has inpatient and outpatient facilities and provides health care services to both the expatriate and local communities.

An airstrip large enough to land a small jet is also located north of Londolovit, at Kunaye.

As is the case in many tropical regions, mosquito-borne viruses are present on the island, as is malaria.

Land ownership follows traditional models with land being owned by clans. Insofar as it relates to land ownership, the society is matrilineal with land being passed through the female generations. The land cannot be sold; however, usage rights can be granted.

The Island has two largest Primary Schools and a Secondary School Located on the Mining impacted area. The largest of the two Primary schools is Sekunkun Primary School which is on the North Eastern part of the Island. The school has total of over 600 students and 19 teachers.

Lord Howe Seamount Chain

The Lord Howe Seamount Chain is one of the two parallel seamount chains alongside the east coast of Australia; the Lord Howe and Tasmantid seamount chains both run north-south through parts of the Coral Sea and Tasman Sea. These chains have longitudes of approximately 159°E and 156°E respectively.The Lord Howe Seamount Chain has been known under a variety of different gazetted names, including the Lord Howe Seamounts, Lord Howe Guyots, Lord Howe Rise Guyots and the Middleton Chain.The Lord Howe Seamount Chain is on the western slope of Lord Howe Rise, a deep-sea elevated plateau which is a submerged part of Zealandia. The Tasmantid and Lord Howe seamount chains are both broadly within the Tasman basin (the abyssal plain between Lord Howe Rise and the Australian continental shelf), and lie on opposite sides of Dampier Ridge (a submerged continental fragment).The Lord Howe Seamount Chain extends from the Chesterfield group (20°S) to Flinders Seamount (34.7°S). It includes Nova Bank, Argo and Kelso seamounts, Capel and Gifford guyots, Middleton and Elizabeth reefs, Lord Howe Island and Ball's Pyramid.The Lord Howe and Tasmantid chains each resulted from the Indo-Australian Plate moving northward over a stationary hotspot; the hotspot for the Lord Howe chain is expected to presently be beneath Flinders Seamount. On the Australian mainland, a third north-south sequence of extinct volcanoes (which includes the Glass House Mountains) is likely to have the same origin.The chain formed during the Miocene. It features many coral-capped guyots.

Louisville hotspot

The Louisville hotspot is a volcanic hotspot responsible for the volcanic activity that has formed the Louisville Ridge in the southern Pacific Ocean.

Mackenzie Large Igneous Province

The Mackenzie Large Igneous Province (MLIP) is a major Mesoproterozoic large igneous province of the southwestern, western and northwestern Canadian Shield in Canada. It consists of a group of related igneous rocks that were formed during a massive igneous event starting about 1,270 million years ago. The large igneous province extends from the Arctic in Nunavut to near the Great Lakes in Northwestern Ontario where it meets with the smaller Matachewan dike swarm. Included in the Mackenzie Large Igneous Province are the large Muskox layered intrusion, the Coppermine River flood basalt sequence and the massive northwesterly trending Mackenzie dike swarm.

As a large igneous province, it is an extremely large area of related igneous rocks that were emplaced over an extremely short geological time span. The igneous rocks comprising the Mackenzie Large Igneous Province originated from processes not associated with normal plate tectonics and seafloor spreading. It is one of the several large igneous provinces scattered throughout the Canadian landscape, which can be thousands of kilometres in volume and area. The Mackenzie Large Igneous Province is one of the world's largest Proterozoic magmatic provinces, as well as one of the most well-preserved continental flood basalt terrains on Earth. Igneous rocks of the Mackenzie Large Igneous Province are generally mafic in composition, including basalt and gabbro.

Even though the Mackenzie Large Igneous Province is classified as a large igneous province like other extremely large accumulations of igneous rocks on Earth, it is much larger than large igneous province standards. The standard size classification for large igneous provinces is a minimum areal extent of 100,000 km2 (39,000 sq mi). However, the Mackenzie dike swarm itself occupies an area of at least 2,700,000 km2 (1,000,000 sq mi), making the Mackenzie Large Igneous Province larger than the Ontong Java Plateau (in the southwestern Pacific Ocean) and the U.S. state of Alaska.

Majorite

Majorite is a type of garnet mineral found in the mantle of the Earth. Its chemical formula is Mg3(MgSi)(SiO4)3. It is distinguished from other garnets in having Si in octahedral as well as tetrahedral coordination. Majorite was first described in 1970 from the Coorara Meteorite of Western Australia and has been reported from various other meteorites in which majorite is thought to result from an extraterrestrial high pressure shock event. Mantle derived xenoliths containing majorite have been reported from potassic ultramafic magmas on Malaita Island on the Ontong Java Plateau Southwest Pacific.

North Fiji Basin

The North Fiji Basin (NFB) is an oceanic basin west of Fiji in the south-west Pacific Ocean. It is an actively spreading back-arc basin delimited by the Fiji islands to the east, the inactive Vitiaz Trench to the north, the Vanuatu/New Hebrides island arc to the west, and the Hunter fracture zone to the south.

Roughly triangular in shape with its apex located at the northern end of the New Hebrides Arc, the basin is actively spreading southward and is characterised by three spreading centres and an oceanic crust younger than 12 Ma. The opening of the NFB began when a slab roll-back was initiated beneath the New Hebrides and the island arc started its clockwise rotation.

The opening of the basin was the result of the collision between the Ontong Java Plateau and the Australian Plate along the now inactive Solomon–Vitiaz subduction system north of the NFB.

The NFB is the largest and most developed back-arc basin of the south-west Pacific. It is opening in a complex geological setting between two oppositely verging subduction systems, the New Hebrides/Vanuatu and Tonga trenches and hence it's ocean floor has the World's largest amount of spreading centres per area.Two opposite-facing systems of deformation partly overlap where the Australian and Pacific plates meet along a section of the andesite line in the south-west Pacific: east of the NFB the Kermadec-Tonga Arc stretches some 3,000 km (1,900 mi) north from New Zealand, and west of the NFB the New Hebrides subduction zone formed during the opening of the NFB back-arc basin.There are three microplates in the NFB: New Hebrides, Balmoral Reef, and Conway Reef.Little was known about the NFB before 1985 and in the 1970s the central part of the basin, the only mapped area, was called the North Fiji Plateau.

Ontong

Ontong is a surname. Notable people with the surname include:

Justin Ontong (born 1980), South African cricketer

Rodney Ontong (born 1955), former English first-class cricketer

Shaun Ontong (born 1987), Australian football player

Ontong Java Atoll

Ontong Java Atoll or Luangiua is one of the largest atolls on earth. It is sometimes referred to as Lord Howe Atoll, not to be confused with Lord Howe Island.

Geographically it belongs to a scattered group of three atolls which includes nearby Nukumanu Atoll and the wholly submerged Roncador Reef located 75 kilometres (47 miles) to the south.

Supervolcano

A supervolcano is a large volcano that has had an eruption with a Volcanic Explosivity Index (VEI) of 8, the largest recorded value on the index. This means the volume of deposits for that eruption is greater than 1,000 cubic kilometers (240 cubic miles).

Supervolcanoes occur when magma in the mantle rises into the crust but is unable to break through it and pressure builds in a large and growing magma pool until the crust is unable to contain the pressure. This can occur at hotspots (for example, Yellowstone Caldera) or at subduction zones (for example, Toba). Large-volume supervolcanic eruptions are also often associated with large igneous provinces, which can cover huge areas with lava and volcanic ash. These can cause long-lasting climate change (such as the triggering of a small ice age) and threaten species with extinction. The Oruanui eruption of New Zealand's Taupo Volcano (about 26,500 years ago) was the world's most recent VEI-8 eruption.

Tamu Massif

Tamu Massif is an extinct submarine shield volcano in the northwest Pacific Ocean, with the characteristics of a hybrid between a mid-ocean ridge and a shield volcano. On 5 September 2013, researchers announced that it could be a single volcano, which if corroborated, would make Tamu Massif the largest known volcano on Earth. Tamu Massif is located in the Shatsky Rise about 1,600 km (990 mi) east of Japan. The volcano, which comprises the entire Skatsky Rise, covers an area of about 553,000 square kilometres (214,000 sq mi), making Tamu Massif the largest known volcano in the solar system, in terms of surface area. Its summit is about 1,980 m (6,500 ft) below the surface of the ocean, and its base extends to about 6.4 km (4.0 mi) deep. The volcano is about 4,460 metres (14,620 ft) tall.

William Sager, a marine geophysicist from the Department of Earth and Atmospheric Sciences at the University of Houston, began studying the volcano in about 1993 at the Texas A&M College of Geosciences. According to Sager and his team, Tamu Massif is "the biggest single shield volcano ever discovered on Earth". Other igneous features on the planet are larger, such as the Ontong Java Plateau, but it has not yet been determined if they are indeed just one volcano or rather complexes of several volcanoes.

Tweed Volcano

Tweed Volcano is a partially eroded Early Miocene shield volcano located in northeastern New South Wales, which formed when this region of Australia passed over the East Australia hotspot around 23 million years ago. Mount Warning, Lamington Plateau and the Border Ranges between New South Wales and Queensland are among the remnants of this volcano that was originally over 100 kilometres (62 mi) in diameter and nearly twice the height of Mount Warning today, at 1,156 metres (3,793 ft). Despite its size, Tweed Volcano was not a supervolcano; other shield volcanoes - such as on Hawaii - are much larger. In the 23 million years since the volcano was active, erosion has been extensive, forming a large erosion caldera around the volcanic plug of Mount Warning. Its erosion caldera is the largest in the Southern Hemisphere.

Volcanic plateau

A volcanic plateau is a plateau produced by volcanic activity. There are two main types: lava plateaus and pyroclastic plateaus.

Zuñi sequence

The Zuñi sequence was the major cratonic sequence after the Absaroka sequence that began in the latest Jurassic, peaked in the late Cretaceous, and ended by the start of the following Paleocene. Though it was not the final major transgression, it was the last complete sequence to cover the North American craton; the following Tejas sequence was much less extensive.

Languages

This page is based on a Wikipedia article written by authors (here).
Text is available under the CC BY-SA 3.0 license; additional terms may apply.
Images, videos and audio are available under their respective licenses.