The water cycle drives geological processes at the surface. The fact that water coexists as fluid, vapor and solid is crucial in shaping the Earth's surface. The fact that conditions in the upper mantle can readily convert eclogite to magma to basalt, and back, with enormous density changes, is crucial in global magmatism and tectonics. Phase changes in the mafic components of the upper mantle are larger than thermal expansion effects and they drive the eclogite engine.

There are several ways to generate massive melting in the mantle; one is to bring hot material adiabatically up from depth until it melts; the other is to insert low-melting point fertile material – delaminated lower arc-crust, for example – into the mantle from above and allow the mantle to heat it up. Both mechanisms may be involved in the formation of large igneous provinces – LIPs. The timescale for heating and recycling of lower-crust material is much less than for subducted oceanic crust because the former starts out much hotter and does not sink as deep.

The standard petrological models for magma genesis involve a homogenous pyrolite mantle, augmented at times by small-scale pyroxenite veins or recycled oceanic crust. It is increasingly being recognized that large blocks of eclogite in the mantle may be an important fertility source. Delaminated continental crust differs in many important respects from recycled MORB.