Marquesas Hotspot
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The Marquesas hotspot is a
volcanic A volcano is commonly defined as a vent or fissure in the crust of a planetary-mass object, such as Earth, that allows hot lava, volcanic ash, and gases to escape from a magma chamber below the surface. On Earth, volcanoes are most often fo ...
hotspot in the southern
Pacific Ocean The Pacific Ocean is the largest and deepest of Earth's five Borders of the oceans, oceanic divisions. It extends from the Arctic Ocean in the north to the Southern Ocean, or, depending on the definition, to Antarctica in the south, and is ...
. It is responsible for the creation of the
Marquesas Islands The Marquesas Islands ( ; or ' or ' ; Marquesan language, Marquesan: ' (North Marquesan language, North Marquesan) and ' (South Marquesan language, South Marquesan), both meaning "the land of men") are a group of volcano, volcanic islands in ...
– a group of eight main islands and several smaller ones – and a few
seamount A seamount is a large submarine landform that rises from the ocean floor without reaching the water surface (sea level), and thus is not an island, islet, or cliff-rock. Seamounts are typically formed from extinct volcanoes that rise abruptly a ...
s. The islands and seamounts formed between 5.5 and 0.4 million years ago and constitute the northernmost volcanic chain in
French Polynesia French Polynesia ( ; ; ) is an overseas collectivity of France and its sole #Governance, overseas country. It comprises 121 geographically dispersed islands and atolls stretching over more than in the Pacific Ocean, South Pacific Ocean. The t ...
. There are two competing theories concerning the origins of volcanism associated with the Marquesas hotspot. Many geoscientists maintain that the area is underlain by a
mantle plume A mantle plume is a proposed mechanism of convection within the Earth's mantle, hypothesized to explain anomalous volcanism. Because the plume head partially melts on reaching shallow depths, a plume is often invoked as the cause of volcanic ho ...
which has transported hot material from the lower mantle to the surface, forming the chain of islands and seamounts as the Pacific Plate moved in a north-westerly direction relative to the stationary plume.
Radiometric dating Radiometric dating, radioactive dating or radioisotope dating is a technique which is used to Chronological dating, date materials such as Rock (geology), rocks or carbon, in which trace radioactive impurity, impurities were selectively incorporat ...
of the youngest volcanic rocks suggests that volcanism is still active. Evidence for a plume origin comes mainly from seismic imaging, with large-scale low velocity anomalies being observed from the core-mantle boundary to around 1000 km depth and interpreted as a superplume, and smaller, shallow anomalies interpreted as narrow secondary plumes generated by the superplume.
Geochemical Geochemistry is the science that uses the tools and principles of chemistry to explain the mechanisms behind major geological systems such as the Earth's crust and its oceans. The realm of geochemistry extends beyond the Earth, encompassing the ...
analysis of the lavas has also been argued to favour a deep-mantle source, though the extent to which source depth can be determined by lava geochemistry has been disputed. Some features of the Marquesas, such as the trend of the islands and seamounts, non-fixity of the source, and short-lived volcanic activity, have been argued to conflict with the plume model. The trend of the chain and non-fixity of the source, however, may be explained by the plume conduit either being deflected by convection currents in the upper mantle or melt being channelled through zones of structural weakness. Volcanic activity may be much longer-lived if the plume also created Hess Rise and Shatsky Ridge to the northwest, both of which follow the same trend as the Marquesas and are dated at 100 Ma and 145–125 Ma respectively. Nevertheless, some scientists dispute the plume model, arguing instead that volcanic activity associated with the Marquesas hotspot and others in the southern Pacific results from shallow tectonic processes. In this interpretation, volcanism in the Marquesas is a consequence of intraplate stresses caused primarily by reorganisations of plate boundaries and thermal contraction of the lithosphere. These processes, it is argued, have generated a system of fissures which enable pre-existing melt in the crust and upper mantle to escape to the surface. The primary evidence for this interpretation is the timing of volcanic activity and orientation of the Marquesas chain, which coincide closely with major reorganisations of plate boundaries and consequent changes in the lithospheric stress field.


See also

* Arago hotspot *
Rarotonga hotspot The Rarotonga hotspot is a volcanic hotspot in the southern Pacific Ocean. The hotspot is claimed to be responsible for the formation of Rarotonga and some volcanics of Aitutaki but an alternative explanation for these islands most recent volca ...


References

{{Hotspots Hotspots of the Pacific Ocean Geography of French Polynesia