Macdonald hotspot

The Macdonald Hotspot is a hotspot located in the southern Pacific Ocean . It is located below the Macdonald seamount of the same name at the southeast end of the Austral Islands of French Polynesia .

designation

The Macdonald hotspot was named after the American volcanologist Gordon A. MacDonald .

Geographical location

World map with the major hotspots. The Macdonald hotspot in the South Pacific is number 24

The Macdonald hotspot is located below the seamount of the same name at the southeast end of the Austral Islands, about 340 kilometers southeast of Marotiri . He is directly responsible for the Macdonald Seamount and possibly also for the further northwest adjoining volcanic chain of the Austral and Cook Islands . However, age dating suggests that other hotspots besides the Macdonald Seamount were involved in these two island chains. Tokelau , the Gilbert Islands , the Phoenix Islands and several seamounts and islands in the Marshall Islands are also likely to go back to the Macdonald hotspot.

Regional geological overview

Hotspots are usually as Manteldiapire ( English mantle plumes ) in the oceanic crust generate magmas explains. However, they may also arise from the reactivation of old lithospheric structures - for example, fractures that had formed under tensile stress. In addition to the Macdonald Seamount, active volcanoes on Hawai'i , the Bounty Seamount on Pitcairn , Vailulu'u on Samoa and Mehetia / Teahitia in the Society Islands are also considered hotspots.

Volcanism in the South Pacific is mostly associated with the so-called South Pacific Superswell - an area that is up to 700 meters higher on average than the rest of the ocean floor. There are several short-lived volcanic chains in it, including the aforementioned hotspots plus the Arago hotspot , the Marquesas Islands and Rarotonga . A swelling region under the South Pacific Superswell could be identified using seismic methods in the earth's mantle , but this was only vaguely recorded by tomography due to the lack of seismic measuring stations. In the specific case of the Macdonald hotspot, it looks as if a low-speed anomaly in the Earth's mantle extends from a depth of 1000 kilometers to the surface, but at the same time a far more extensive anomaly located below 1000 kilometers. This observation has been linked to a superplume , a giant mantle diapir. Superplumes example, also be deemed to be caused huge oceanic plateaus, the out of the chalk originating Ontong Java Plateau . Superplumes arise at the Earth's core / mantle boundary and then split into secondary hotspots in the upper mantle, as seems to be the case with the Macdonald hotspot and the hotspot of the Society Islands.

Geology of the Australian and Cook Islands

The volcanic structures of the Australian and Cook Islands very probably owe their existence to the Macdonald hotspot, over which the Pacific Plate slid at an average speed of 100 to 110 millimeters / year in a west-northwest direction. The Austral Islands are underlain by a 300 to 500 meter high topographic bulge (English swell ) up to the volcanically active Macdonald Seamount at their southeastern end . The archipelago obviously conforms to a chronologically linear sequence, as they (with the exception of Marotiri, which was exposed to wave erosion due to a lack of fringing reef ) are progressively less affected by erosion morphologically towards the southeast. However, they are found near the Guyots archipelago , some of which have secondary volcanoes. These guyots may be much older and their secondary volcanism may be due to lithospheric anomalies that were periodically activated and generated new magmas.

In addition, age dating has shown that there is no clear age sequence based on the Macdonald Seamount in the Cook-Austral chain. In reality the chain seems to be composed of two different lineaments . For their distance from the Macdonald Seamount, Atiu and Aitutaki are extremely young, and Rarotonga is 18 to 19 million years younger than a situation on the Macdonald trend would suggest. In the case of the younger volcanic rocks on Rurutu , another hotspot has to be used, the Arago hotspot . The older volcanic rocks Rurutus are on the Macdonald trend. Tubuai and Raivavae, on the other hand, are too old to have been produced by the Macdonald hotspot - the same applies to rock samples from the deeper base areas of some volcanoes. It is possible that these comparatively old examples were generated by the Foundation hotspot . Note: Turner and Jarrard (1982) also found that Tubuai and Raivavae were younger.

The variable chemical composition between the individual islands poses an additional problem. Some of the Cook Islands also do not lie directly on the reconstructed lineament of the Macdonald hotspot. These discrepancies can actually only be explained by the presence of several hotspots. The reawakening of the dormant volcanism, as in the case of Rurutu, is likely to be due to the crossing of another hotspot.

The high helium-3 to helium-4 ratio encountered is generally considered to be an indication that magmas from hotspot volcanoes originate in the earth's deep mantle. The helium samples from the Macdonald Seamount confirm this and speak against a crustal source of the magmas. The possibility of the existence of lithospheric sectors permeated with primitive helium enrichment cannot be ruled out.

Volcanic structures on the hotspot course

The following volcanic structures were possibly caused by the Macdonald hotspot:

• Macdonald Seamount.
• Rá-Seamount . Although it lies on the lineament, it is too old.
• Marotiri , Rapa , Raivavae , Tubuai and the older volcanic rocks of Rurutu . Isotope analyzes confirm the correlation. Between Raivavae and Rapa there is a change in the isotopic composition, which may be caused by crossing the Austral Fracture Zone . On Marotiri, too, as on the Rá-Seamount, they were found to be too old, possibly both going back to the same magma hearth.
• Neilson Bank . The only known age of questionable quality is too old.
• ZEP 2-19 (Seamount) with a possible age of 8.8 million years ( Miocene , Tortonian ).
• Mangaia .
• Rarotonga . Volcanism mainly took place in the Oligocene , but younger ages are also known.
• Rose Atoll and Malulu Seamount ( Samoa ), if their age of 40 million years ( Eocene , Bartonian ) is correct.
• Tokelau , based on plate reconstructions and isotope data.
• Gilbert Islands . As in the case of the Hawaii-Emperor chain, which is not of the same age, this would mean a kink in the lineament.
• Phoenix Islands , 43 to 66 million years old (Eocene, Lutetian , to Upper Cretaceous, Maastrichtian ).
• The northern Marshall Islands . They were between 100 and 150 million years ago ( Tithonium to Albium ) above the Macdonald hotspot. Later, some seamounts and atolls were affected by the Arago Hotspot, the Rarotonga Hotspot, and the Society Islands Hotspot - resulting in a complex volcanic event and uplift.
  • The Central Cretaceous Guyot Aean-Kan .
  • The northern Ralik chain . It was possibly also shaped by the Macdonald hotspot, but uncertainties in the plate reconstruction 90 million years ago ( Turonium ) raise doubts.
  • Erikub Atoll . The Arago hotspot came much closer, however.
  • The Lokkworkwor seamount and the Lomjenaelik seamount with late Cretaceous volcanism.
  • The Lobbadede-Guyot and the Lewa-Guyot with volcanism of the Aptian and Albian. At Lobbadede-Guyot, volcanism revived because of the Arago hotspot 82.4 million years ago ( Campanium ).
  • The Lo-En-Seamount from the Albium.
  • Wodejebato-Seamount and Ruwituntun-Seamount with volcanism of the Aptium / Albium. The two seamounts were later also recorded by the Arago hotspot - at the same time there was volcanic activity on Bikini Atoll and Rongelap .

Photo gallery

• 

  Marotiri

• 

  Rapa

• 

  Tubuai

• 

  Rurutu

• 

  Rimatara

• 

  Mangaia

• 

  Rarotonga

• 

  Rose Atoll

• 

  Tokelau, Atafu Atoll

• 

  Erikub Atoll

Individual evidence

1. ↑ Morgan, W. Jason and Morgan, Jason Phipps: Plate velocities in a hotspot frame . 2007.
2. ^ WJ Morgan: Convection Plumes in the Lower Mantle . In: Nature . tape 230 (5288) , 1971, pp. 42 , doi : 10.1038 / 230042a0 .
3. ↑ Binard, N., Hekinian, R., Stoffers, P. and Cheminée, JL: South Pacific Intraplate Volcanism: Structure, Morphology and Style of Eruption . In: Oceanic Hotspots . Springer, Berlin, Heidelberg 2004, pp. 157-207 , doi : 10.1007 / 978-3-642-18782-7_6 .
4. ↑ Tanaka, S. et al .: P-wave tomography of the mantle beneath the South Pacific Superswell revealed by joint ocean floor and islands broadband seismic experiments . In: Physics of the Earth and Planetary Interiors . tape 172 (3-4) , 2009, pp. 268-277 , doi : 10.1016 / j.pepi.2008.10.016 .
5. ↑ Suetsugu, Daisuke and Hanyu, Takeshi: Origin of hotspots in the South Pacific: Recent advances in seismological and geochemical models . In: Geochemical Journal . tape 47 (2) , 2013, p. 259-284 , doi : 10.2343 / geochemj.2.0229 .
6. ↑ Talandier, Jacques and Okal, Emile A .: New surveys of MacDonald Seamount, southcentral Pacific, following volcanoseismic activity, 1977-1983 . In: Geophysical Research Letters . tape 11 (9) , 1984, ISSN  1944-8007 , pp. 813-816 , doi : 10.1029 / GL011i009p00813 .
7. ↑ Bideau, D. and Hekinian, R .: Intraplate Gabbroic rock debris Ejected from the Magma Chamber of the Macdonald seamount (Austral Hotspot): Comparison with Other Provinces . In: Oceanic Hotspots . Springer, Berlin, Heidelberg 2004, pp. 309-348 , doi : 10.1007 / 978-3-642-18782-7_11 .
8. ↑ Johnson, Rockne H. and Malahoff, Alexander: Relation of Macdonald Volcano to migration of volcanism along the Austral Chain . In: Journal of Geophysical Research . tape 76 (14) , 1971, ISSN  2156-2202 , pp. 3282-3290 , doi : 10.1029 / JB076i014p03282 .
9. ↑ Thompson, GM, Malpas, J. and Smith, Ian EM: Volcanic geology of Rarotonga, southern Pacific Ocean . In: New Zealand Journal of Geology and Geophysics . tape 41 (1) , 2010, p. 95 , doi : 10.1080 / 00288306.1998.9514793 .
10. ↑ Dalrymple, G. Brent, Jarrard, RD and Clague, DA: K-Ar ages of some volcanic rocks from the Cook and Austral Islands . In: GSA Bulletin . tape 86 (10) , 1975, ISSN  0016-7606 , pp. 1466 , doi : 10.1130 / 0016-7606 (1975) 86 <1463: KAOSVR> 2.0.CO; 2 .
11. ↑ McNutt, MK, Caress, DW, Reynolds, J., Jordahl, KA and Duncan, RA: Failure of plume theory to explain midplate volcanism in the southern Austral islands . In: Nature . tape 389 (6650) , 1997, ISSN  0028-0836 , pp. 479-482 , doi : 10.1038 / 39013 .
12. ^ Turner, DL and Jarrard, RD: K-Ar dating of the Cook-Austral Island chain: a test of the hot spot hypothesis . In: J. volcanol. qeothermal Res. Volume 12 , 1982, pp. 187-220 .
13. ↑ Fleitout, L. and Moriceau, C .: Short-wavelength geoid, bathymetry and the convective pattern beneath the Pacific Ocean . In: Geophysical Journal International . tape 110 (1) , 1992, ISSN  0956-540X , pp. 13 , doi : 10.1111 / j.1365-246X.1992.tb00709.x .
14. ↑ Moreira, Manuel and Allègre, Claude: Helium isotopes on the Macdonald seamount (Austral chain): constraints on the origin of the superswell . In: Comptes Rendus Geoscience . tape 336 (11) , 2004, pp. 983-990 , doi : 10.1016 / j.crte.2004.04.0 .
15. ↑ Chauvel, C., McDonough, W., Guille, G., Maury, R. and Duncan, R .: Contrasting old and young volcanism in Rurutu Island, Austral chain . In: Chemical Geology . tape 139 (1-4) , 1997, pp. 125-143 , doi : 10.1016 / s0009-2541 (97) 00029-6 .
16. ↑ Woodhead, Jon D .: Extreme HIMU in an oceanic setting: the geochemistry of Mangaia Island (Polynesia), and temporal evolution of the Cook — Austral hotspot . In: Journal of Volcanology and Geothermal Research . tape 72 (1-2) , 1996, pp. 16 , doi : 10.1016 / 0377-0273 (96) 00002-9 .
17. ^ Bonneville, Alain et al.: Arago Seamount: The missing hotspot found in the Austral Islands . In: Geology . tape 30 (11) , 2002, ISSN  0091-7613 , pp. 1023-1026 , doi : 10.1130 / 0091-7613 (2002) 030 <1023: ASTMHF> 2.0.CO; 2 .
18. ↑ Sipkin, Stuart A. and Jordan, Thomas H .: Lateral heterogeneity of the upper mantle determined from the travel times of ScS . In: Journal of Geophysical Research . tape 80 (11) , 1975, pp. 1479 , doi : 10.1029 / JB080i011p01474 .
19. ↑ Jackson, Matthew G. et al: Samoan hot spot track on a "hot spot highway": Implications for mantle plumes and a deep Samoan mantle source . In: Geochemistry, Geophysics, Geosystems . tape 11 (12) , 2010, pp. 19 , doi : 10.1029 / 2010GC003232 .
20. ↑ Konter, JG, Koppers, AA, Staudigel, H., Hanan, BB and Blichert-Toft, J: Intermittent Volcanism in the S Pacific: Tracking Persistent Geochemical Sources . In: AGU Fall Meeting Abstracts . tape 51 , 2001.
21. ^ Jarrard, Richard D. and Clague, David A .: Implications of Pacific Island and seamount ages for the origin of volcanic chains . In: Reviews of Geophysics . tape 15 (1) , 1977, pp. 57 , doi : 10.1029 / RG015i001p00057 .
22. ^ Bergersen, DD: Cretaceous Hotspot Tracks through the Marshall Islands . 1995, doi : 10.2973 / odp.proc.sr.144.018.1995 .
23. ↑ 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. 34 , doi : 10.1016 / 0012-821x (91) 90015-a .
24. ↑ Lincoln, Jonathan M., Pringle, Malcolm S., and Silva, Isabella Premoli: Early and Late Cretaceous Volcanism and Reef-Building in the Marshall Islands . In: The Mesozoic Pacific: Geology, Tectonics, and Volcanism . American Geophysical Union, 1993, pp. 279-305 , doi : 10.1029 / gm077p0279 .