Mantle plumes: dynamics and geochemical signature

Abstract

[EN] Mantle plumes constitute a secondary type of convection. Their total heat flow represents 10% of the mantle heat loss, corresponding aproximately to 8% of the global Earth´s heat budget. Mantle plumes originate at the D” core-mantle boundary as a result of the thermal destabilization triggered by the core heat. They ascent towards the base of the lithosphere with a nearly spherical-shaped head followed by an elongated tail connected to the D’’ source area. During this upwelling process, plume heads liberate some of their heat into the neighbouring mantle zones, which they also partly assimilate. Plumes are constituted by differentially enriched zones, as evidenced by the chemical composition of basalts in continental flood provinces, oceanic plateaux, and oceanic islands, which are supposed to be the result of plume activity. The geochemical and isotopic data of the last 15 years show that the more enriched domain is not uniform, and that at least three contrasted components can be identified: HIMU, EM1, and EM2. The HIMU component is enriched in high field strength elements and it is strongly radiogenic in Pb. The EM1 component is enriched in both large ion lithophile elements and light rare earth elements and it displays slightly elevated Sr isotopic relationships being also depleted in radiogenic Nd and Pb. Finally, the EM2 component is enriched in large ion lithophile elements, it is highly radiogenic in Sr, and its Nd and Pb isotopic values are intermediate between the two other components. The most widely accepted hypothesis suggests that the HIMU component derived from altered and dehydrated oceanic crust (~3%), while the EM1 and EM2 components represent a mixture between the HIMU component and a small percentage of previously dehydrated 1500-2000 Ma-old pelagic and terrigenous sediments. The less enriched domain is constituted by a mantle characterized by low 87Sr/86Sr and high Nd, Pb and He isotopic ratios. This component, called FOZO (Focus Zone), PHEM (Primitive Helium Mantle) and C (Common Component), is thought to be derived from the lower mantle.

[ES] Las plumas constituyen un modo de convección secundario. Su flujo de calor total representa el 10% del calor que emerge a través del manto y el 8% del que globalmente pierde la Tierra. Se originan en el límite manto-núcleo, por la desestabilización que genera el calor que desprende el núcleo en la capa D”. Ascienden hacia la base de la litosfera adoptando la forma de una cabeza más o menos esférica, seguida de un tallo que conecta con su zona-fuente. Durante su ascenso la cabeza transmite parte de su exceso térmico al material que atraviesa, por lo que asimila una parte del mismo.