Arago hotspot

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The Arago hotspot is the oldest hotspot in the Pacific Ocean . It is located below the Arago Seamount near Rurutu in the Australian Islands of French Polynesia . Its activity dates back to the aptium around 120 million years .

designation

The Arago hotspot was named after the Arago ship of the French Navy, whose crew discovered it in 1993. The ship bears the name of the French astronomer François Arago . The Polynesians knew about the existence of the seamount, which they called Tinomana , lying in a water depth of 27 meters . Previously, the hotspot was also known as the Rurutu hotspot - a misleading term, as it was also used to refer to an older volcanic chain that began at Raivavae .

Geological introduction

Map with the hotspots of the earth. The Arago hotspot is # 59.

The Arago hotspot is one of a group of hotspots in the South Pacific, including the Society hotspot and the Macdonald hotspot . Although hotspots are located in the earth's crust , they are very deep structures that are caused by mantle diapirs and manifest themselves as volcanoes on the surface . The origin of the Arago hotspot is likely to be in the upper mantle and is therefore comparatively shallow.

As the Pacific plate moves over the hotspot, the resulting volcanic building moves away from its magma center and a new volcano takes its place. The movement of the plate can also cause an existing, older volcano to slide over the hotspot and then be lifted out. This happened, for example, in Rurutu.

The Arago hotspot is directly responsible for the creation of the recent Arago seamount and for the uplift of Rurutu. However, plate reconstructions from the last 120 million years show that some other islands and seamounts can also be traced back to the Arago hotspot. This very likely includes Tuvalu , the Gilbert Islands , the Ratak chain of the Marshall Islands and parts of the Austral Islands and the Cook Islands .

Geolographic location and general geology

The islands of French Polynesia

The Arago hotspot, named after the deep sea mountain of the same name, is located 130 kilometers southeast of Rurutu. It comes to rest on the so-called South Pacific Superswell - an area of ​​the South Pacific measuring 3,000 × 3,000 kilometers, which towers over the rest of the ocean by an average of 700 meters. This high region probably sits above a huge mantle diapir, which should reach down to the mantle core boundary , in turn splitting into secondary plumes and then revealing itself as several hotspots in the oceanic crust . In addition to the Arago hotspot , the South Pacific Superswell includes the Macdonald hotspot , the Marquesas hotspot , the Pitcairn hotspot and the society hotspot . Only the Macdonald hotspot and the society hotspot should be very profound. The volcanism in the Superswell area, however, still leaves many questions unanswered.

The Arago Seamount is part of the volcanic chain of the Austral and Cook Islands . In this chain of around 2,200 kilometers, consisting of two atolls and eleven islands, two very different directions can be identified. Only the Macdonald Seamount is still active among their volcanoes. The radiometric ages of the volcanic islands follow roughly a regular trend. The younger ages of Aitutaki and Rurutu as well as their different chemical composition suggest, however, that another hotspot must also be present.

The Arago and other hotspots are probably not deep mantle diapirs, but much shallower structures that are petrologically influenced by the lithosphere . This assumption is supported by the lack of a submarine plateau, which is usually formed by deep plumes. The origin of the Arago hotspot is likely to be the upper coat. Evaluations of the magnitude of seismic speed anomalies (as well as their sign) below the Arago seamount are contradictory. A seismic tomography from 2009 could only detect a weak anomaly down to a depth of 100 kilometers, but found no evidence of a deeper mantle root. Currently, the Arago and Macdonald hotspots are the only guaranteed active hotspots in the Austral Islands. The hotspot responsible for Rarotonga may also still be active. Other hotspots in the area are Tubuai , the Taukina Seamounts and the Ngatemato Seamounts .

Description of the seamount

The Arago-Seamount is a composite volcano, which, comparable to Rurutu, has three rift zones. It is made up of three individual volcanoes, with one overlapping the other two. Potassium-argon dating showed an age of 230,000 ± 4,000 years BP ( Pleistocene ) and a recent result. The underlying oceanic crust is around 80 million years old and comes from the Campanium .

As with so many submarine volcanoes, mass movements have also taken place on the Arago Seamount , recognizable by the trailing edges on the north, east and west flanks. Its very young Pleistocene age suggests that the seamount emerged from a hotspot. In contrast to the Macdonald Seamount, however, no historical volcanic eruptions are known on the Arago Seamount.

It is possible that other hotspots also contributed to the build-up of the composite volcano. Isotope analyzes of 8.2 million year old rock samples from the Arago Seamount suggest a genetic relationship to the Raivavae hotspot and the President Thiers Bank hotspot . Other volcanoes in the neighborhood also show that they did not emerge from just a single hotspot. The magma ascent may have been channeled and facilitated through weak zones in the lithosphere.

geochemistry

Hotspot provinces in the Pacific. The Arago hotspot is part of the Macdonald Province.

The Pacific plate moved at a very high speed of up to 120 millimeters / year over the Arago hotspot, which could create several volcanoes and drift away with the plate. The lead isotope ratios of the volcanic rocks of the Arago hotspot have a clear HIMU component, they are therefore very radiogenic and resemble the younger volcanic rocks of Rurutu. It is possible that volcanic rocks from the Arago hotspot were recycled back into the earth's mantle and their melting then mixed under magmas from the northeastern Lau basin . There is also the possibility that seamount material was first subducted into the Tonga Trench and then later erupted in the Lau Basin (the Tonga Trench is located near the reconstructed hotspot course). But HIMU xenolites were also discovered on Tubai, which is located southeast of the Arago seamount.

Other associated islands and seamounts

Rurutu is older and was formed in the Miocene ( Serravallian ) 13 million years ago over the Macdonald hotspot. Than in the Pleistocene slid years ago 1 million over the Arago hotspot and lava flows basanitischer and Hawaiian genetic composition. In addition, the island and its fringing reef were raised 150 meters. Prominent coral reefs (also known as Makatea ) had aroused the interest of geologists very early (as early as 1840), who speculated about their origins. Other upscale atolls are to the northwest of Rurutu, and they too owe their origins to the Arago hotspot.

The following volcanic islands are very likely to be traced back to the Arago Seamount:

  • Rurutu, singled out about 1 million years ago.
  • The seamounts ZEP 2-6, ZEP 2-7 and ZEP 2-8 near Rurutu, with a similar morphological structure.
  • Rimatara .
  • Seamount ZEP 2-12 near Rimatara, formed 2.6 million years ago.
  • Mangaia , originated 19 million years ago. Also associated with the Macdonald hotspot.

There is a possible connection to:

  • Îles Maria . Could also overlay another hotspot at the moment.
  • Mitiaro .
  • Takutea .
  • Manuae .
  • Atiu and Mauke . Both islands have the HIMU component, but different neodymium isotope ratios.
  • Palmerston .
  • Several seamounts in western Samoa that were formed together with Tuvalu between 63 and 42 million years ago.
  • Tuvalu . The formation of the island in the period 70 to 50 million years preceded the "kink" in the course of the seamount chain, comparable to the Hawaii-Emperor chain . Isotope ratios of trace elements support this assumption.
  • Gilbert Islands , formed 70 to 64 million years ago. Isotope data support this, but in this case it must be concluded that the Arago hotspot has drifted slightly.
  • Tokelau . Rather, the isotope ratios indicate a genetic relationship to the Macdonald hotspot. Tokelau also place plate reconstructions over the Macdonald hotspot.
  • Ratak chain of the Marshall Islands , formed 100 to 74 million years ago. One theory says that not only the Arago hotspot, but also other hotspots were involved in the gradual development of the chain. In this case, too, a plate reconstruction causes the Arago hotspot to migrate.
    • These include the guyots Wodejebato and Limalok . The Wodejebato-Guyot is said to have moved 85 million years ago over the Arago hotspot, a sample of its volcanic rock showed an age of 84.4 million years. The Limalok Guyot is a little younger at 75 million years old and crossed the hotspot much later. Strontium and lead isotope ratios of the Wodejebato-Guyot are very similar to the ratios of the Arago-Seamount.
    • Woden-Kopakut-Guyot . It is between 83.8 and 80.6 million years old. It is said to have moved over the Arago hotspot 82 million years ago.
    • Eniwetok and Lo-En-Guyot . They too must have crossed the path of the Arago hotspot. However, there is no evidence of volcanism for the period of their crossing (90 to 85 million years), with the exception of broken glass from Lo-En-Guyot from the Campanium . However, plate reconstructions result in a far too far south location for Lo-En.
  • The over 100 million year old West Pacific Seamount Province .
  • The 150 to 100 million year old Marcus Wake Seamounts . These include the less than 87 million year old Lamont guyot , the 97 million year old Miami guyot and the 91 million year old wild guyot . Both isotope ratios and plate tectonic reconstructions suggest that the Marcus Wake Seamounts were generated by the Arago hotspot. However, it has not yet been possible to sample all of the guyots.
  • Volcanism in the 117 million year old Eastern Mariana Basin .
  • Doleritic dykes, drilled in 1992 on the ocean floor in the Eastern Mariana Basin, which are 126.1 ± 0.6 million years old. Their geochemical composition is comparable to the chemistry of the Arago Seamount and in reconstructions they come to lie above the Arago Seamount.
  • The Himu and Golden Dragon Seamounts , both around 120 million years old. With a similar composition to the Arago Seamount.

The volcanic lineaments end in the Mariana Trench , but older material may have been accreted in the forearc of the trench.

The oldest volcanic structures are a good 120 million years old. If this dating is correct, the Arago hotspot would be the oldest hotspot in the Pacific Ocean, ahead of the Hawaii hotspot and the Louisville hotspot . This view is not shared by all geoscientists, however; There is also the opinion that the seamount chain is actually based on only a few datable volcanoes and was therefore relatively short-lived.

Tubuai lies ahead of the Arago hotspot in the southeast and will not pass over it for a few million years. As was the case with Rurutu, there will then be uplift and renewed volcanic activity.

Photo gallery

  • Rurutu

  • Rimatara

  • Mangaia

  • Îsles Maria

  • Mitiaro

  • Takutea

  • Manuae

  • Atiu

  • Muck

  • Palmerston Atoll

Individual evidence

  1. ^ Bonneville, Alain et al.: Arago Seamount: The missing hotspot found in the Austral Islands . In: Geology . tape 30 (11) , 2002, ISSN  0091-7613 , doi : 10.1130 / 0091-7613 (2002) 030 <1023: ASTMHF> 2.0.CO; 2 .
  2. ^ Price, Allison A. et al .: Geochemical evidence in the northeast Lau Basin for subduction of the Cook-Austral volcanic chain in the Tonga Trench . In: Geochemistry, Geophysics, Geosystems . tape 17 (5) , 2015, ISSN  1525-2027 , pp. 1694-1724 , doi : 10.1002 / 2015GC006237 .
  3. ↑ Suetsugu, D., Isse, T., Tanaka, S., Obayashi, M., Shiobara, H., Sugioka, H., Kanazawa, T., Fukao, Y. and Barruol, G .: South Pacific mantle plumes imaged by seismic observation on islands and seafloor . In: Geochemistry, Geophysics, Geosystems . tape 10 (11) , 2009, ISSN  1525-2027 , pp. Q11014 , doi : 10.1029 / 2009GC002533 .
  4. ↑ Isse, Takehi, Sugioka, Hiroko, Ito, Aki, Shiobara, Hajime, Reymond, Dominique and Suetsugu, Daisuke: Upper mantle structure beneath the Society hotspot and surrounding region using broadband data from ocean floor and islands . In: Earth, Planets and Space . tape 68 , 2016, ISSN  1880-5981 , p. 33 , doi : 10.1186 / s40623-016-0408-2 .
  5. ↑ Binard, N., Hekinian, R., Stoffers, P. and Cheminée, JL: Oceanic Hotspots . Springer, Berlin, Heidelberg 2004, ISBN 978-3-642-62290-8 , pp. 157-207 , doi : 10.1007 / 978-3-642-18782-7_6 .
  6. ^ Neall, Vincent E. and Trewick, Steven A .: The age and origin of the Pacific islands: a geological overview . In: Philosophical Transactions of the Royal Society of London B: Biological Sciences . tape 363 (1508) , 2008, ISSN  0962-8436 , p. 3293-3308 , doi : 10.1098 / rstb.2008.0119 .
  7. ^ Bonneville, Alain, Dosso, Laure and Hildenbrand, Anthony: Temporal evolution and geochemical variability of the South Pacific superplume activity . In: Earth and Planetary Science Letters . tape 244 (1-2) , 2005, pp. 251-269 , doi : 10.1016 / j.epsl.2005.12.037 .
  8. ↑ Clouard, V.und Bonneville, A .: Submarine Mass Movements and Their Consequences . In: Advances in Natural and Technological Hazards Research . Springer, Dordrecht 2003, ISBN 978-94-010-3973-4 , pp. 337 , doi : 10.1007 / 978-94-010-0093-2_37 .
  9. ↑ Clouard, V. and Bonneville, A .: Oceanic Hotspots . Springer, Berlin, Heidelberg 2004, ISBN 978-3-642-62290-8 , pp. 227-228 , doi : 10.1007 / 978-3-642-18782-7_7 .
  10. ^ Morgan, W. Jason and Morgan, Jason Phipps: Plate velocities in hotspot reference frame: electronic supplement . 2007.
  11. ↑ Jackson, MG et al .: Deeply dredged submarine HIMU glasses from the Tuvalu Islands, Polynesia: Implications for volatile budgets of recycled oceanic crust . In: Geochemistry, Geophysics, Geosystems . tape 16 (9) , 2015, ISSN  1525-2027 , pp. 3210–3234 , doi : 10.1002 / 2015gc005966 .
  12. ↑ Koppers, AAP, Staudigel, Hubert, Christie, DM H, Dieu, JJ and Pringle, MJ: Sr-Nd-Pb Isotope Geochemistry of Leg 144 West Pacific Guyots: Implications for the Geochemical Evolution of the "SOPITA" Mantle Anomaly . 1995, doi : 10.2973 / odp.proc.sr.144.031.1995 .
  13. ^ Etienne, Samuel: Landscapes and Landforms of France. World Geomorphological Landscapes . Springer, Dordrecht 2014, ISBN 978-94-007-7021-8 , pp. 253 , doi : 10.1007 / 978-94-007-7022-5_24 .
  14. ^ Bergersen, DD: Cretaceous Hotspot Tracks through the Marshall Islands . 1995, doi : 10.2973 / odp.proc.sr.144.018.1995 .
  15. ^ Adam, C. and Bonneville, A .: No thinning of the lithosphere beneath northern part of the Cook-Austral volcanic chains . In: Journal of Geophysical Research: Solid Earth . 113 (B10), 2007, ISSN  2156-2202 , pp. B10104 , doi : 10.1029 / 2007jb005313 .
  16. ↑ Finlayson, V., Konter, JG, Konrad, K., Price, AA, Koppers, AAP and Jackson, MG: Identification of a Hawaiian-Emperor Style Bend in the Tuvalu Segment of the Rurutu Hotspot . In: AGU Fall Meeting Abstracts . tape 52 , 2016.
  17. ↑ Finlayson, V., Konter, JG, Konrad, K., Koppers, AAP and Jackson, MG: The Rurutu Hotspot: Isotopic and Trace Element Evidence of HIMU Hotspot Volcanism in the Tuvalu Islands . In: AGU Fall Meeting Abstracts . tape 33 , 2014.
  18. ↑ Konter, Jasper G., Hanan, Barry B., Blichert-Toft, Janne, Koppers, Anthony AP, Plank, Terry and Staudigel, Hubert: One hundred million years of mantle geochemical history suggest the retiring of mantle plumes is premature . In: Earth and Planetary Science Letters . tape 275 (3-4) , 2008, pp. 285-295 , doi : 10.1016 / j.epsl.2008.08.023 .
  19. ^ Haggerty, JA and Silva, I. Premoli: Comparison of the Origin and Evolution of Northwest Pacific Guyots Drilled during Leg 144 . 1995, doi : 10.2973 / odp.proc.sr.144.074.1995 .
  20. ↑ Ozima, M., Honda, Masahiko and Saito, K .: 40Ar-39Ar ages of guyots in the western Pacific and discussion of their evolution . In: Geophysical Journal International . tape 51 (2) , 1977, ISSN  0956-540X , pp. 475-485 , doi : 10.1111 / j.1365-246x.1977.tb06930.x .
  21. ^ Pringle, MS: Radiometric Ages of Basaltic Basement Recovered at Sites 800, 801, and 802, Leg 129, Western Pacific Ocean . 1992, doi : 10.2973 / odp.proc.sr.129.130.1992 .
  22. ↑ Staudigel, Hubert, Park, K.-H., Pringle, M., Rubenstone, JL, Smith, WHF and Zindler, A .: The longevity of the South Pacific isotopic and thermal anomaly . In: Earth and Planetary Science Letters . tape 102 (1) , 1991, pp. 31 , doi : 10.1016 / 0012-821x (91) 90015-a .
  23. ^ Franco, Heather and Abbott, Dallas: Gravity signatures of terrane accretion . In: Lithos . tape 46 (1) , 1998, pp. 6 , doi : 10.1016 / S0024-4937 (98) 00060-7 .
  24. ↑ Koppers, AA, Konter, JGund Jackson, MG: Insights Into the Origin of the Longest-lived Hotspot in the Pacific: Clues from the Tuvalus . In: AGU Fall Meeting Abstracts . 2013.