The Marquesas hotspot is a

volcanic A volcano is a rupture 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 found where tectonic plates are ...

hotspot Hotspot, Hot Spot or Hot spot may refer to: Places * Hot Spot, Kentucky, a community in the United States Arts, entertainment, and media Fictional entities * Hot Spot (comics), a name for the DC Comics character Isaiah Crockett * Hot Spot (Tr ...

in the southern

Pacific Ocean The Pacific Ocean is the largest and deepest of Earth's five oceanic divisions. It extends from the Arctic Ocean in the north to the Southern Ocean (or, depending on definition, to Antarctica) in the south, and is bounded by the contin ...

. It is responsible for the creation of the

Marquesas Islands The Marquesas Islands (; french: Îles Marquises or ' or '; Marquesan: ' ( North Marquesan) and ' ( South Marquesan), both meaning "the land of men") are a group of volcanic islands in French Polynesia, an overseas collectivity of France in ...

– a group of eight main islands and several smaller ones – and a few

seamount A seamount is a large geologic landform that rises from the ocean floor that does not reach to the water's surface (sea level), and thus is not an island, islet or cliff-rock. Seamounts are typically formed from extinct volcanoes that rise abr ...

s. The islands and seamounts formed between 5.5 and 0.4 million years ago and constitute the northernmost volcanic chain in

French Polynesia )Territorial motto: ( en, "Great Tahiti of the Golden Haze") , anthem = , song_type = Regional anthem , song = " Ia Ora 'O Tahiti Nui" , image_map = French Polynesia on the globe (French Polynesia centered).svg , map_alt = Location of Frenc ...

. 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 hots ...

which has transported hot material from the lower mantle to the surface, forming the chain of islands and seamounts as the

Pacific Plate The Pacific Plate is an oceanic tectonic plate that lies beneath the Pacific Ocean. At , it is the largest tectonic plate. The plate first came into existence 190 million years ago, at the triple junction between the Farallon, Phoenix, and Iza ...

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 date materials such as rocks or carbon, in which trace radioactive impurities were selectively incorporated when they were formed. The method compares ...

of the youngest volcanic rocks suggests that volcanism is still active. Evidence for a plume origin comes mainly from

seismic imaging Geophysical imaging (also known as geophysical tomography) is a minimally destructive geophysical technique that investigates the subsurface of a terrestrial planet. Geophysical imaging is a noninvasive imaging technique with a high parametrical ...

, 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 A lithosphere () is the rigid, outermost rocky shell of a terrestrial planet or natural satellite. On Earth, it is composed of the crust and the portion of the upper mantle that behaves elastically on time scales of up to thousands of years o ...

stress field.

References

Hotspots of the Pacific Ocean Geography of French Polynesia {{FrenchPolynesia-geo-stub

See also

References