{{Short description|Pacific volcanic hotspot}} right|thumb|450px|The Society hotspot is marked 38 on the map. The '''Society hotspot''' is a volcanic hotspot in the south Pacific Ocean which is responsible for the formation of the Society Islands, an archipelago of fourteen volcanic islands and atolls spanning around {{convert|720|km}} of the ocean. These islands, which include Tahiti, Mo'orea and Bora bora, range in age from 4.5 million years to less than 1 million years.<ref name="Trewick2008">{{cite journal |last1=Neall |first1=V.E. |last2=Trewick |first2=S.A. |date=2008 |title=The age and origin of the Pacific islands: A geological overview |journal=Philosophical Transactions of the Royal Society of London B |volume=363 |issue=1508 |pages=3293–3308 |doi=10.1098/rstb.2008.0119|pmid=18768382 |pmc=2607379 }}</ref>
==Formation== There are currently two main hypotheses concerning the cause of volcanic activity. The conventional view is that the hotspot is underlain by a mantle plume which has transported hot material from the lower mantle to the surface, creating the chain as the Pacific Plate has moved northwest over the plume.<ref name="Rhodes2001">{{cite journal |last1=Rhodes |first1=M. |last2=Davies |first2=J.H. |date=2001 |title=Tomographic imaging of multiple mantle plumes in the uppermost lower mantle |journal=Geophysical Journal International |volume=147 |issue=1 |pages=88–92 |doi=10.1046/j.0956-540x.2001.01512.x|bibcode=2001GeoJI.147...88R |doi-access=free }}</ref><ref name="Niu2002">{{cite journal |last1=Niu |first1=F. |last2=Solomon |first2=S.C. |last3=Silver |first3=P.G. |last4=Suetsugu |first4=D. |last5=Inoue | first5=H. |date=2002 |title=Mantle transition-zone structure beneath the South Pacific Superswell and evidence for a mantle plume underlying the Society hotspot |url=https://www.sciencedirect.com/science/article/pii/S0012821X0200523X |journal=Earth and Planetary Science Letters |volume=198 |issue=3–4 |pages=371–380 |doi=10.1016/S0012-821X(02)00523-X|bibcode=2002E&PSL.198..371N |url-access=subscription }}</ref><ref name="Koppers2003">{{cite journal |last1=Koppers |first1=A.A.P. |last2=Staudigel |first2=H. |last3=Pringle |first3=M.S. |last4=Wijbrans |first4=J.R. |date=2003 |title=Short‐lived and discontinuous intraplate volcanism in the South Pacific: Hot spots or extensional volcanism? |url=https://agupubs.onlinelibrary.wiley.com/doi/full/10.1029/2003GC000533 |journal=Geochemistry, Geophysics, Geosystems |volume=4 |issue=10 |page=1089 |doi=10.1029/2003GC000533|bibcode=2003GGG.....4.1089K |s2cid=131213793 |url-access=subscription }}</ref><ref name="French2015">{{cite journal |last1=French |first1=S.W. |last2=Romanowicz |first2=B. |date=2015 |title=Broad plumes rooted at the base of the Earth's mantle beneath major hotspots |url= https://www.nature.com/articles/nature14876 |journal=Nature |volume=525 |issue=7567 |pages=95–99 |doi=10.1038/nature14876|pmid=26333468 |bibcode=2015Natur.525...95F |s2cid=205245093 |url-access=subscription }}</ref><ref name="Cordier2016">{{cite journal |last1=Cordier |first1=C. |last2=Chauvel |first2=C. |author-link2=Catherine Chauvel|last3=Hémond |first3=C. |date=2016 |title=High-precision lead isotopes and stripy plumes: Revisiting the Society chain in French Polynesia |url=https://www.sciencedirect.com/science/article/pii/S0016703716303192 |journal=Geochimica et Cosmochimica Acta |volume=189 |issue=15 |pages=236–250 |doi=10.1016/j.gca.2016.06.010|bibcode=2016GeCoA.189..236C |url-access=subscription }}</ref>
Several lines of evidence support this interpretation. Age progression along the chain is consistent with estimates of the velocity of plate motion.<ref name="Trewick2008"/> Seismic anomalies have been observed in the upper mantle<ref name="Isse2006">{{cite journal |last1=Isse |first1=T. |last2=Suetsugu |first2=D. |last3=Shiobara |first3=H. |last4=Sugioka |first4=H. |last5=Yoshizawa | first5=K. |last6=Kanazawa |first6=T. |last7=Fukao |first7=Y. |date=2006 |title=Shear wave speed structure beneath the South Pacific superswell using broadband data from ocean floor and islands |journal=Geophysical Research Letters |volume=33 |issue=16 |pages=L16303 |doi=10.1029/2006GL026872|bibcode=2006GeoRL..3316303I |doi-access=free |hdl=2115/52170 |hdl-access=free }}</ref><ref name="Isse2016">{{cite journal |last1=Isse |first1=T. |last2=Sugioka |first2=H. |last3=Ito |first3=A. |last4=Shiobara |first4=H. |last5=Reymond | first5=D. |last6=Suetsugu |first6=D. |date=2016 |title=Upper mantle structure beneath the Society hotspot and surrounding region using broadband data from ocean floor and islands |journal=Earth, Planets and Space |volume=68 |issue=33 |page=33 |doi=10.1186/s40623-016-0408-2|bibcode=2016EP&S...68...33I |doi-access=free }}</ref> and found to extend into the uppermost lower mantle, implying that the passage of hot material from the lower to upper mantle is not hindered by the transition zone.<ref name="Rhodes2001"/> Magnetotelluric imaging has found higher conductivity in the upper mantle under the active area southeast of Tahiti consistent with anomalously hot rising material.<ref name="Nolasco1998">{{cite journal |last1=Nolasco |first1=R. |last2=Tarits |first2=P. |last3=Filloux |first3=J.H. |last4=Chave |first4=A.D. |date=1998 |title=Magnetotelluric imaging of the Society Islands hotspot |journal=Journal of Geophysical Research |volume=103 |issue=B12 |pages=30287–30309 |doi=10.1029/98JB02129|bibcode=1998JGR...10330287N |doi-access=free }}</ref><ref name="Tada2016">{{cite journal |last1=Tada |first1=N. |last2=Tarits |first2=P. |last3=Baba |first3=K. |last4=Utada |first4=H. |last5=Kasaya | first5=T. |last6=Suetsugu |first6=D. |date=2016 |title=Electromagnetic evidence for volatile‐rich upwelling beneath the society hotspot, French Polynesia |url=https://agupubs.onlinelibrary.wiley.com/doi/full/10.1002/2016GL071331 |journal=Geophysical Research Letters |volume=43 |issue=23 |pages=12021–12026 |doi=10.1002/2016GL071331|bibcode=2016GeoRL..4312021T |s2cid=132297145 }}</ref>
There are two competing versions of the mantle plume model. One version posits a narrow, discreet plume feeding only the Society hotspot.<ref name="Rhodes2001"/><ref name="Niu2002"/> The other proposes a superplume with narrow conduits supplying several hotspots in the south Pacific.<ref name="Koppers2003"/><ref name="French2015"/> Evidence for the former model includes magnetotelluric imaging which finds conductivity anomalies of less than {{convert|150|km}} in radius indicating a plume of limited extent<ref name="Nolasco1998"/> and seismic imaging of the transition zone under the Society hotspot which shows a thinned area of less than {{convert|500|km}} implying that the thermal flux from lower to upper mantle is on the scale of a plume rather than a superplume.<ref name="Niu2002"/> Evidence for the latter model includes seismic imaging of the lower mantle which reveals a large-scale low-velocity anomaly from the base of the mantle to around {{convert|1000|km}} depth, small-scale anomalies in the upper mantle which may be narrow plumes generated by the superplume<ref name="French2015"/><ref name="Suetsugu2009">{{cite journal |last1=Suetsugu |first1=D. |last2=Isse |first2=T. |last3=Tanaka |first3=S. |last4=Obayashi |first4=M. |last5=Shiobara | first5=H. |last6=Sugioka |first6=H. |last7=Kanazawa |first7=T. |last8=Fukao |first8=Y. |last9=Barruol |first9=G. |last10=Reymond |first10=D. |date=2009 |title=South Pacific mantle plumes imaged by seismic observation on islands and seafloor |url=https://agupubs.onlinelibrary.wiley.com/doi/full/10.1029/2009GC002533 |journal=Geochemistry, Geophysics, Geosystems |volume=10 |issue=11 |pages=n/a |doi=10.1029/2009GC002533|bibcode=2009GGG....1011014S |s2cid=52267924 |url-access=subscription }}</ref> and intermittent volcanic activity in south Pacific hotspots which contrasts with the persistent volcanism expected for individual plumes.<ref name="Koppers2003"/>
Clouard and Bonneville 2001 have argued that certain features of the Society hotspot, such as the lack of an initial flood basalt at the old end of the chain, short-lived volcanic activity,<ref name="Clouard2001">{{cite journal |last1=Clouard |first1=V. |last2=Bonneville |first2=A. |date=2001 |title=How many Pacific hotspots are fed by deep-mantle plumes? |url=https://pubs.geoscienceworld.org/gsa/geology/article-abstract/29/8/695/192078/How-many-Pacific-hotspots-are-fed-by-deep-mantle?redirectedFrom=fulltext |journal=Geology |volume=29 |issue=8 |doi=10.1130/0091-7613(2001)029<0695:HMPHAF>2.0.CO;2|bibcode=2001Geo....29..695C |url-access=subscription }}</ref> and petrological and geochemical analysis of the lavas which reveals a number of shallow-source components,<ref name="Natland2005">{{cite book |last1=Natland |first1=J.H. |last2=Winterer |first2=E.L. |editor-last1=Foulger |editor-first1=G.R. |editor-last2=Natland |editor-first2=J.H. |editor-last3=Presnall |editor-first3=D.C. |editor-last4=Anderson |editor-first4=D.L. |title=Plates, plumes, and paradigms: Geological Society of America Special Paper 388 |publisher=Geological Society of America |date=2005 |pages=687–710 |chapter=Fissure control on volcanic action in the Pacific |isbn=9780813723884 |doi=10.1130/0-8137-2388-4.687 }}</ref> are inconsistent with the plume model and have proposed a tectonic origin. According to this model, the Society and other volcanic chains in the south Pacific result from a system of fissures caused by intraplate stresses related to thermal contraction of the lithosphere, subduction-induced flow of the asthenosphere, and changes in the configuration of plate boundaries which have enabled pre-existing melt in the crust and shallow mantle to escape to the surface.<ref name="Natland2005"/><ref name="Hieronymus2000">{{cite journal |last1=Hieronymus |first1=C.F. |last2=Bercovici |first2=D. |author-link2=David Bercovici|date=2000 |title=Non-hotspot formation of volcanic chains: Control of tectonic and flexural stresses on magma transport |url=https://www.sciencedirect.com/science/article/pii/S0012821X00002272 |journal=Earth and Planetary Science Letters |volume=181 |issue=4 |pages=539–554 |doi=10.1016/S0012-821X(00)00227-2|bibcode=2000E&PSL.181..539H |url-access=subscription }}</ref><ref name="Smith2003">{{cite journal |last1=Smith |first1=A.D. |date=2003 |title=A reappraisal of stress field and convective roll models for the origin and distribution of Cretaceous to recent intraplate volcanism in the Pacific basin |url=https://www.tandfonline.com/doi/abs/10.2747/0020-6814.45.4.287 |journal=International Geology Review |volume=45 |issue=4 |pages=287–302 |doi=10.2747/0020-6814.45.4.287|bibcode=2003IGRv...45..287S |s2cid=129463020 |url-access=subscription }}</ref><ref name="Peive2007">{{cite journal |last1=Peive |first1=A.A. |date=2007 |title=Linear volcanic chains in oceans: Possible formation mechanisms |url=https://link.springer.com/article/10.1134/S0016852107040024 |journal=Geotectonics |volume=41 |issue=4 |pages=281–295 |doi=10.1134/S0016852107040024|bibcode=2007Geote..41..281P |s2cid=128409663 |url-access=subscription }}</ref> The timing of volcanic activity and orientation of the chain, both of which coincide closely with major alterations in plate boundary configurations and consequent changes in the lithospheric stress field and direction of asthenospheric counterflow, support this model.<ref name="Smith2003"/><ref name="Natland2005"/>
Some of the above features, however, can be accommodated by the plume model. The lack of initial flood basalt and short-lived activity, for example, are consistent with some versions of the superplume model which propose small-scale intermittent "plumelets" generated by the superplume,<ref name="Koppers2003"/> and the petrology and geochemistry of the lavas may be due to subducted oceanic crust being sampled by the plume.<ref name="Cordier2016"/>
==See also==
* Arago hotspot * Rarotonga hotspot * Tarava Seamounts
==References== {{reflist}}
{{coord|17|32|S|149|50|W|type:isle|display=title}} {{DEFAULTSORT:Society Hotspot}} Category:Hotspots of the Pacific Ocean Category:Society Islands
{{Hotspots}}