Pitcairn hotspot

The Pitcairn hotspot is a volcanic hotspot located in the south-central Pacific Ocean. Over the past 11 million years, it has formed the Pitcairn-Gambier hotspot chain. It is responsible for creating the Pitcairn Islands and two large seamounts named Adams and Bounty, as well as atolls at Moruroa, Fangataufa and the Gambier Islands. The hotspot is currently located at Adams and Bounty, which are ~60 kilometers East-Southeast of Pitcairn Island.[1]

Location of the Pitcairn Hotspot Chain with Depth Map and Distance Scale
Using GeoMapApp, this picture shows, using gray circles, locations of Moruroa, Fangataufa, Gambier, Pitcairn Island and Pitcairn Hotspots current location from left to right.
Hotspots
The Pitcairn hotspot is marked 31 on map.

Current Hotspot Location

The current hotspot location is west of the spreading center known as the East Pacific Rise; an area near where the Nazca plate and the Pacific plate are diverging around 20°S, 115°W. This is where material is thought to be sourced from the core-mantle boundary, rising to surface as a localized plume.[1] Opponents of the hotspot theory instead attribute Pitcairn hotspot to upwelling at the western end of the Easter Fracture Zone.[2]

Morphology

Multibeam bathymetry shows that the two largest seamounts, Adams and Bounty, rise 2000m above the seafloor. Several other smaller, volcanically active seamounts exist that are shorter than 2000m in height. Bathymetry records have estimated the volume of erupted lava due to volcanic activity to be about 5900 km3 within a radius of about 110 kilometers.[3]

Petrology

The larger edifices show much more extensive volcanic activity and a wider range of compositions than the smaller. The four different types of rocks that are erupted are classified as either picrite basalt, alkali basalt, trachyandesite and trachyte.[4] Areas have been observed on Bounty showing pillow basalts and giant tubular basalt to tabular/blocky trachy-andesite and trachyte flows scattered across the slope of the seamount.[3] Pyroclasts and hyaloclastites have also been observed on the main seamounts displaying a geologic history of the seamounts and past environment around them.[5]

Pitcairn-Gambier hotspot chain

The hotspot has formed a chain of seamounts over the past 11 million years [1] with several other large seamounts along the chain as well, organized from older to younger the further east you go. Some of these islands make up the Pitcairn Islands. They are named the Pitcairn proper, Henderson, Ducie and Oeno. The islands were first discovered by Europeans in 1767 and it is considered one of the most remote islands inhabited on earth.[6] Multibeam bathymetry and bottom imaging has shown there to be hundreds or volcanic structures in a 9500 square kilometer area around the Pitcairn Island area. East of the main island, there are several active volcanoes that are only just below the surface, less than 500 meters deep.[3]

Morphology

Several seamounts makes up the Pitcairn-Gambier hotspot chain. These include Moruroa, now an atoll that formed about 11 Ma, Fangataufa, now an atoll that formed about 10 Ma, Gambier Islands, islands and atolls that formed about 6.5 Ma, Pitcairn Islands about 0.7 Ma and Pitcairn seamounts about 0.5 Ma. This chain spreads from 21.5 degrees S, 139 degrees W to 25 degrees S, 129.5 degrees W.[7]

Geochemistry

The seamount chain has varying ratios of 206Pb/204Pb isotopic composition, ranging from 18.99 to 19.62, depending on how far away from where the hotspot currently lies and how long ago it was formed by the hotspot. Ratios of 87Sr/ 86Sr were calculated to range between 0.70292 and 0.70367 and ratios of 143Nd/144Nd were calculated to be between 0.51303 and 0.51288. Trace element ratios seemed relatively constant during tests.[8]

Formation

Using methods of modeling of lead isotopes, the date set for different rocks around Pitcairn hotspot were estimated to be from 0.6 and 0.7 Ma.[7] The hotspot has four islands that have formed since the hotspot's origin.

See also

References

  1. ^ a b c Global Volcanism Program: Adams Seamount
  2. ^ Milligan, Lucy. "The Easter – Sala y Gomez Volcanic Chain". Mantle Plumes. Retrieved May 29, 2018.
  3. ^ a b c Hekininan, R (March 1, 2003). "The Pitcairn hotspot in the South Pacific: distribution and composition of submarine volcanic sequences". Journal of Volcanology and Geothermal Research. 121 (3–4): 219–245. Bibcode:2003JVGR..121..219H. doi:10.1016/S0377-0273(02)00427-4.
  4. ^ Kendrick, Mark (March 26, 2014). "Contrasting behaviours of CO2, S, H2O and halogens (F, Cl, Br, and I) in enriched-mantle melts from Pitcairn and Society seamounts". Chemical Geology. 370: 69–81. Bibcode:2014ChGeo.370...69K. doi:10.1016/j.chemgeo.2014.01.019.
  5. ^ Ackermand, D (March 3, 1998). "Magmatic sulfides and oxides in volcanic rocks from the Pitcairn hotspot (South Pacific)". Mineralogy and Petrology. 64 (1–4): 149–162. Bibcode:1998MinPe..64..149A. doi:10.1007/BF01226567.
  6. ^ "Pitcairns History". The Government of the Pitcairn Islands. Pitcairn Islands Office. Retrieved May 29, 2018.
  7. ^ a b Delavault, Hélène (November 15, 2016). "Sulfur and lead isotopic evidence of relic Archean sediments in the Pitcairn mantle plume". PNAS. 113 (46): 12952–12956. Bibcode:2016PNAS..11312952D. doi:10.1073/pnas.1523805113. PMC 5135331. PMID 27791057.
  8. ^ Dupuy, Claude (May 15, 1993). "Basalts from Mururoa, Fangataufa and Gambier islands (French Polynesia): Geochemical dependence on the age of the lithosphere". Earth and Planetary Science Letters. 117 (1–2): 89–100. Bibcode:1993E&PSL.117...89D. doi:10.1016/0012-821X(93)90119-T.

Extra

Adams Seamount

Adams Seamount (also known as Forty Mile Reef) is a submarine volcano above the Pitcairn hotspot in the central Pacific Ocean about 100 kilometres (62 mi) southwest of Pitcairn Island.

Arago hotspot

Arago hotspot is a hotspot in the Pacific Ocean, presently located below the Arago seamount close to the island of Rurutu, French Polynesia.

Arago is part of a family of hotspots in the southern Pacific, which include the Society hotspot and the Macdonald hotspot among others. These are structures beneath Earth's crust which generate volcanoes and which are in part formed by mantle plumes, although Arago itself might have a shallower origin. As the Pacific plate moves over the hotspots, new volcanoes form and old volcanoes are carried away; sometimes an older volcano is carried over the hotspot and is then uplifted as happened with Rurutu.

The Arago hotspot is responsible for the formation of Arago seamount and uplift on Rurutu; however reconstructions of the past positions of tectonic plates and geochemistry suggest that other islands and seamounts were constructed by the Arago hotspot during the past 120 million years. These potentially include Tuvalu, Gilbert Islands, the Ratak Chain of the Marshall Islands as well as part of the Austral Islands and Cook Islands.

Bounty Seamount

Bounty Seamount is a seamount in the Pacific Ocean, which reaches a depth of 420 metres (1,380 ft) or 450 metres (1,480 ft). It is about 3,950 metres (12,960 ft) high.

Geology of the Pacific Ocean

The Pacific Ocean evolved in the Mesozoic from the Panthalassic Ocean, which had formed when Rodinia rifted apart around 750 Ma. The first ocean floor which is part of the current Pacific Plate began 160 Ma to the west of the central Pacific and subsequently developed into the largest oceanic plate on Earth.The tectonic plates continue to move today. The slowest spreading ridge is the Gakkel Ridge on the Arctic Ocean floor, which spreads at less than 2.5 cm/year (1 in/year), while the fastest, the East Pacific Rise near Easter Island, has a spreading rate of over 15 cm/year (6 in/year).

Hotspot (geology)

In geology, the places known as hotspots or hot spots are volcanic regions thought to be fed by underlying mantle that is anomalously hot compared with the surrounding mantle. Their position on the Earth's surface is independent of tectonic plate boundaries. There are two hypotheses that attempt to explain their origins. One suggests that hotspots are due to mantle plumes that rise as thermal diapirs from the core–mantle boundary. The other hypothesis is that lithospheric extension permits the passive rising of melt from shallow depths. This hypothesis considers the term "hotspot" to be a misnomer, asserting that the mantle source beneath them is, in fact, not anomalously hot at all. Well-known examples include the Hawaii, Iceland and Yellowstone hotspots.

Musicians Seamounts

Musicians Seamounts are a chain of seamounts in the Pacific Ocean, north of the Hawaiian Ridge. There are about 65 seamounts, some of which are named after musicians. These seamounts exist in two chains, one of which has been attributed to a probably now-extinct hotspot called the Euterpe hotspot. Others may have formed in response to plate tectonics associated with the boundary between the Pacific Plate and the former Farallon Plate.

The seamounts were constructed on young oceanic crust during the Cretaceous, but a second phase of volcanic activity took place during the Eocene. Deep sea coral reefs occur on the seamounts.

Outline of oceanography

The following outline is provided as an overview of and introduction to Oceanography.

Pitcairn Islands

The Pitcairn Islands (; Pitkern: Pitkern Ailen), officially Pitcairn, Henderson, Ducie and Oeno Islands, are a group of four volcanic islands in the southern Pacific Ocean that form the sole British Overseas Territory in the Pacific Ocean. The four islands—Pitcairn proper, Henderson, Ducie and Oeno—are scattered across several hundred miles of ocean and have a combined land area of about 18 square miles (47 km2). Henderson Island accounts for 86% of the land area, but only Pitcairn Island is inhabited. The nearest places are Mangareva (of French Polynesia) to the west and Easter Island to the east.

Pitcairn is the least populous national jurisdiction in the world. The Pitcairn Islanders are a biracial ethnic group descended mostly from nine Bounty mutineers and the handful of Tahitians who accompanied them, an event that has been retold in many books and films. This history is still apparent in the surnames of many of the islanders. Today there are approximately 50 permanent inhabitants, originating from four main families.

Tarava seamounts

The Tarava seamounts are a group of seamounts in the southern Pacific Ocean, southwest of the Society Islands. They are formed by five guyots and a number of cone-shaped seamounts. Of Eocene-Oligocene age, they may have formed under the influence of a hotspot.

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