Lherzolites mantle rocks

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... 

Most of the orogenic spinel Lherzolites also contain small amounts of amphibole ( 1 %) textu-rally equilibrated with the peridotite minerals. These amphiboles have been ascribed to the infiltration of melts/fluids in mantle conditions (Fabries et al., 1991), but their presence is not associated with noticeable chemical enrichments (Vannucci et al., 1995). A possible explanation is that the liquid/rock ratio was so low that the fluid composition was buffered by the LREE-depleted composition of the peridotites. Alternatively, these amphiboles might represent the products of a late crystallization stage during fertilization of the peridotites by LREE-depleted basaltic melts. 

Pearson D. G., Davies G. R., Nixon P. H., and Mattey D. P. (1991b) A carbon isotope study of diamond facies pyroxenites and associated rocks from the Beni Bousera peridotite, north Morocco. In Orogenic Lherzolites and Mantle Processes, Spec. Vol. J. Petrol, (eds. M. A. Menzies, C. Dupuy, and A. Nicolas). Oxford University Press, Oxford, UK, pp. 175-189. 

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