Mantle plumes, convection and decompression melting

Mantle plumes, narrow upwellings of hot rock, owe their origin to the instabilities of the thermal boundary layer either at 670 km depth or at the base of the mantle. These upwellings bring deep mantle material to the base of the lithosphere and are manifested on the earth's surface by positive geoid, bathymetry/topography, heat flow anomalies, and extensive volcanism. The volcanism over a mantle plume occurs due to the partial melting of hot upwelling mantle as a result of decompression. The extent of partial melting depends on the convective velocities which are obtained through a fluid dynamical modelling approach. The partial melting introduces two important effects; the latent heat effect during melting cools the plume, thus reducing the degree of melting, and the melt removal reduces the density of the mantle residue thereby introducing convective instabilities in the system. The effect of these factors on the mantle dynamics and melting rate has been studied. The results indicate formation of a swell root of depleted residue above the plume at the base of lithosphere and reduction in the melt production rate with time-varying fluctuations.