The Rarotonga hotspot is in the Pacific Ocean, between the points 24 and 35 in this map.
TheRarotonga hotspot is avolcanichotspot in the southernPacific Ocean. The hotspot is claimed to be responsible for the formation ofRarotonga and some volcanics ofAitutaki but an alternative explanation for these islands most recent volcanics has not been ruled out.[1] Recently alternatives to hotspot activity have been offered for several other intra-plate volcanoes that may have been associated with the Rarotonga hotspot hypothesis.[2][3]
In addition to these volcanoes in theCook Islands, the composition of volcanic rocks inSamoa and in theLau Basin may have been influenced by the Rarotonga hotspot, and someatolls andseamounts in theMarshall Islands may have formed on the hotspot as well.
Oceanic plateaus and linear volcanic chains dot the floor of thePacific Ocean. Their formation has been explained withmantle plumes which rise from thecore-mantle boundary and spread out when they rise, forming a large "head" that causes intense volcanic activity once it hits thecrust. This volcanism is responsible for the formation of the oceanic plateaus. Later, the remnant "tail" of the plume is still rising and induces the formation of volcano chains as the crust moves over the plume tail, thus forming the linear chains of hot spots.[4] As there is growing evidence that not all intra-plate volcanoes are generated by upwelling mantle plumes, not all may be formed from hot spots.[5]
A number ofhotspots are or were active in the Pacific Ocean and some of these may be the product ofmantle plumes.[4] Other hotspots such as Rarotonga appear to have been active only for short time periods;[6] many of these are located inFrench Polynesia where there is asuperswell. Such hotspot volcanism may be the product of shallow processes.[7] Research has suggested that theMacdonald hotspot, and theRurutu hotspot are long lived hotspots that were active as far back as theCretaceous;[8] so they may be over 100 million years old and in such case the oldest still active hotspots in the Pacific.[9] The Rarotonga hotspot may also be very old[8] but the evidence is less convincing;[5] it is also possible that the "Rarotonga hotspot" is simplyrejuvenated volcanism linked to a different hotspot.[10] These three hotspots[11] may have built theCook-Austral Islands together, resulting in overlapping ages of the volcanoes.[5] A gap between 60-50 million years ago may have been caused by theOntong Java Plateau burying the hotspot.[12]
Seismic tomography has found slow velocity anomalies underneath Rarotonga, down to depths of about 100 kilometres (62 mi)[13] with more recent research indicating that they root at about 1,000 kilometres (620 mi) depth.[14] The anomaly lies at over 80 kilometres (50 mi) depth with no evidence of shallower anomalies, however.[15] The Rarotonga volcanic source and other regional hotspots appear to be anchored to a deep mantle structure that is one of thelarge low-shear-velocity provinces.[5] It is one of four (the others being theMarquesas,Pitcairn andSociety hotspots) Pacific hotspots with the so-called "EM" chemical signature.[16]
The Rarotonga hotspot is linked only to the formation ofRarotonga[6] and to volcanism onAitutaki,[5] as potential volcanic structures between theTonga Trench and Rarotonga that may have been formed by the same hotspot are poorly studied.[17] Rarotonga itself is young but there is little indication of volcanism either southeast or northwest from it[18] and no evidence of its current position.[19]
Other candidate volcanoes/structures formed by the Rarotonga hotspot or influenced by it are:
Rose Atoll and Malulu Seamount may have been formed by the Rarotonga hotspot, but other hotspots are also candidates.[22] The connection to Rarotonga is supported by geochemical traits.[23]
Uo Mamae seamount in Samoa share geochemical traits with the Rarotonga hotspot and plate motion reconstructions indicate that the hotspot track passed through it. Potentially, the hotspot formed Uo Mamae and local tectonic processes later (940,000 years ago) triggeredrejuvenated volcanism.[8]
The composition of rejuvenated volcanism inSamoa may bear traces of the influence of the Rarotonga hotspot, which passed across Samoa in the past.[24]
Reconstructions of the path of the Rarotonga hotspot imply that part of its output wassubducted into theTonga Trench;[25]back-arcmagmas may thus ended up entraining material formerly produced by the Rarotonga hotspot.[8] Backarc volcanic rocks in theLau Basin bear traces of such influence.[9][26]
TheMarshall Islands underwent vigorous volcanic and geological activity while they passed over the Rarotonga hotspot and neighbouring hotspots.[28]
Geochemical traits and plate reconstruction links theRalik Chain to the Rarotonga hotspot less than 80 million years ago,[29] specifically the northern Ralik.[12]
Limalok guyot was close to the Rarotonga and Rurutu hotspots 62 million years ago. The plate reconstructions point towards Rurutu being the origin of Limalok, while geochemical traits match Rarotonga best.[30]
Lo-Enguyot was within the influence of the Rarotonga hotspot between 85 and 74 million years ago; if volcanic activity occurred during that time it may be owing to the effect of this hotspot. There is evidence ofCampanian volcanic activity[31]
Eniwetok was located close to the Rarotonga hotspot about 76.9 million years ago; this date corresponds to the aradiometric age obtained on the upper volcano.[31]
A cluster of volcanoes close to Eniwetok and Ujlan may be the product of the Rarotonga hotspot.[32]
Volcanic activity atWōdejebato coincides with a period where the Rarotonga hotspot, theRurutu hotspot and theTahiti hotspot were all three located close to the seamount.[31]
Geochemical traits and plate reconstruction links theMagellan Seamounts to the Rarotonga hotspot less than 80 million years ago[29] although other hotspots also played a role[33] - in particular, mantle previously altered by theArago hotspot[34] such as atPako Guyot.[35] However the Cretaceous intraplate volcanism in the Magellanguyots can be explained by either plume activity or decompression partial melting of oceanic lithosphere caused byPacific Plate deformation and fracturing from the Lithosphere-Asthenosphere Boundary (LAB) level.[2] Some volcanoes may have formed from magma derived from the Rarotonga hotspot, but then channelled to some distance from the actual plume.[36]
TheWestern Pacific Seamount Province has been argued to be theCretaceous path of the Rarotonga hotspot,[8] but its older members appear to be offset slightly north of the reconstructed path.[37] Some seamounts on the reconstructed path of the Rarotonga hotspot share geochemical traits with the hotspot, but with differentleadisotope ratios.[38] However to date there is evidence for at least two formation hypotheses in this area being volcanics derived from partial melting of secondary plume clusters emanating from the top of mantle plumes trapped at the mantle transition zone or secondary plumelets emanating from the top of the Pacificlarge low shear velocity province (LLSVP).[3]
Hemler Guyot has similar isotope ratios as Rarotonga and its reconstructed position match those of the Rarotonga hotspot[39] although some lateral flow of magma may be required to explain its position and that of several other Magellan Seamounts.[40]
^abPeretyazhko, Igor S.; Savina, Elena A. (2022). "Cretaceous intraplate volcanism of Govorov Guyot and formation models of the Magellan seamounts, Pacific Ocean".International Geology Review.65 (16):2479–2505.doi:10.1080/00206814.2022.2145512.S2CID254011792.
^Isse, T.; Sugioka, H.; Ito, A.; Shiobara, H.; Reymond, D.; Suetsugu, D. (December 2015). "Upper mantle structures beneath the South Pacific superswell region using broadband data from ocean floor and islands".AGU Fall Meeting Abstracts.2015: S23D–2771.Bibcode:2015AGUFM.S23D2771I.
^Obayashi, M.; Yoshimitsu, J.; Sugioka, H.; Ito, A.; Isse, T.; Shiobara, H.; Reymond, D.; Suetsugu, D. (28 November 2016). "Mantle plumes beneath the South Pacific superswell revealed by finite frequency tomography using regional seafloor and island data".Geophysical Research Letters.43 (22): 6.Bibcode:2016GeoRL..4311628O.doi:10.1002/2016GL070793.S2CID132379807.
^Koppers, Anthony A. P.; Russell, Jamie A.; Roberts, Jed; Jackson, Matthew G.; Konter, Jasper G.; Wright, Dawn J.; Staudigel, Hubert; Hart, Stanley R. (July 2011). "Age systematics of two young en echelon Samoan volcanic trails".Geochemistry, Geophysics, Geosystems.12 (7): 5.Bibcode:2011GGG....12.7025K.doi:10.1029/2010GC003438.hdl:1912/4769.S2CID54947952.
^Konter, J. G.; Jackson, M. G.; Koppers, A. A. (December 2011). "Tracking Long-lived Hotspots to Constrain Temporal Mantle Compositional Evolution".AGU Fall Meeting Abstracts.2011: DI22A–04.Bibcode:2011AGUFMDI22A..04K.
^abKonter, Jasper G.; Hanan, Barry B.; Blichert-Toft, Janne; Koppers, Anthony A.P.; Plank, Terry; Staudigel, Hubert (November 2008). "One hundred million years of mantle geochemical history suggest the retiring of mantle plumes is premature".Earth and Planetary Science Letters.275 (3–4):292–293.Bibcode:2008E&PSL.275..285K.doi:10.1016/j.epsl.2008.08.023.ISSN0012-821X.
^A >100 Ma Mantle Geochemical Record: Retiring Mantle Plumes may be Premature (December 2006). "A >100 Ma Mantle Geochemical Record: Retiring Mantle Plumes may be Premature".AGU Fall Meeting Abstracts.2006: V34B–01.Bibcode:2006AGUFM.V34B..01K.{{cite journal}}: CS1 maint: numeric names: authors list (link)
^Smith, Walter H. F.; Staudigel, Hubert; Watts, Anthony B.; Pringle, Malcolm S. (10 August 1989). "The Magellan seamounts: Early Cretaceous record of the South Pacific isotopic and thermal anomaly".Journal of Geophysical Research: Solid Earth.94 (B8): 10520.Bibcode:1989JGR....9410501S.doi:10.1029/jb094ib08p10501.ISSN0148-0227.
^Wei, Xun; Zhang, Yan; Shi, Xuefa; Zhang, Hui (June 2024). "Geochronological and geochemical constraints on the petrogenesis and geodynamic process of Hemler, Vlinder, and Il'ichev seamount lavas in NW Pacific".Science China Earth Sciences.67 (6): 1867.doi:10.1007/s11430-024-1327-0.
Jackson, Matthew G.; Hart, Stanley R.; Konter, Jasper G.; Koppers, Anthony A. P.; Staudigel, Hubert; Kurz, Mark D.; Blusztajn, Jerzy; Sinton, John M. (December 2010). "Samoan hot spot track on a "hot spot highway": Implications for mantle plumes and a deep Samoan mantle source".Geochemistry, Geophysics, Geosystems.11 (12): n/a.Bibcode:2010GGG....1112009J.doi:10.1029/2010GC003232.S2CID131425199.
Konter, Jasper G.; Finlayson, Valerie A.; Engel, Jacqueline; Jackson, Matthew G.; Koppers, Anthony A. P.; Sharma, Shiv K. (June 2019). "Shipboard Characterization of Tuvalu, Samoa, and Lau Dredge Samples Using Laser-Induced Breakdown Spectroscopy (LIBS)".Applied Spectroscopy.73 (6):623–637.doi:10.1177/0003702819830793.
Wei, Xun; Zhang, Yan; Shi, Xue-Fa; Castillo, Paterno R; Xu, Yi-Gang; Yan, Quan-Shu; Liu, Ji-Hua (1 April 2022). "Co-Occurrence of HIMU and EM1 Components in a Single Magellan Seamount: Implications for the Formation of West Pacific Seamount Province".Journal of Petrology.63 (4).doi:10.1093/petrology/egac022.
