Harzburgite lower mantle

Figure 10 Temperature dependence of the bulk sound velocity versus depth in the lower mantle, for candidate bulk compositions for the basaltic layer (red), the underlying harzburgite layer (green), and the basal Iherzolite (blue). Note that temperature sensitivity falls with increasing depth.

Similar results have been reported by Mattern et al. (2002), using more recent equations of state for lower-mantle minerals and incorporating the solubility of alumina in silicate perovskite. They also used a three-layered slab model (midocean ridge basalt (MORE) over harzburgite over pyrolite), but with a MORE composition (Si/(Mg - - Fe) = 2.29) intermediate between our extreme end-members of the Helffrich et al. (1989) eclogite (1.65) and the Helffrich and Stein (1993) gabbro (2.58). 

Mantle rocks may be classified into those which are relatively enriched in the elements Ca, Al, Ti, and Na and those which are not. Lherzolites are "enriched" peridotites and are thought to be mantle rocks which have not melted and are known as "fertile" mantle -mantle from which a basaltic melt has not been extracted. Typically they contain a few percent of clinopyroxene and an aluminum-rich mineral (plagioclase, spinel, or garnet) in addition to the statutory olivine and orthopyroxene. Mantle which has experienced melt extraction is known as "depleted" mantle and has lower concentrations of the elements Ca, Al, Ti, and Na. This type of mantle is represented by the rock types harzburgite (peridotite without clinopyroxene and an aluminous mineral) and dunite. The relationship between a fertile mantle Iherzolite, depleted mantle harzburgite/ dunite and a basaltic melt is... 

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