Macdonald hotspot

[13] They fit the pattern of linear volcanism, seeing as they are progressively less degraded southeastward (with the exception of Marotiri, which unprotected by coral reefs unlike the other more equatorial islands has been heavily eroded) and the active Macdonald volcano lies at their southeastern end.

[14] However, there appear to be somewhat older guyots in the area as well, some of which show evidence that secondary volcanoes formed on them.

[16][17] Additional younger ages in some volcanoes such as Rurutu have been explained by the presence of an additional system, the Arago hotspot,[18] and some rocks from Tubuai and Raivavae[17] as well as deeper samples taken on other volcanoes appear to be too old to be explained by the Macdonald hotspot.

[22] The high ratio of helium-3 to helium-4 has been used to infer a deep mantle origin of magmas of hotspot volcanoes.

[23] Helium samples taken from Macdonald support the contention[24] and have been used to rule out the notion that such magmas may be derived from the crust, although an origin in primitive-helium-enriched sectors of the lithosphere is possible.