Clinopyroxenes eclogite xenoliths

Clinopyroxenes in eclogite xenoliths have convex-upwards REE patterns that are LREE-enriched relative to HREE. (La) varies from slightly below 1 to —15, while (Yb) varies between 0.1 and 1.5 (Figure 50). As with garnet, Nb-Ta depletions and, to some extent, other HFSE abundances depend on the coexistence of rutile (Jacob and Foley, 1999 Rudnick et al., 2000 Barth et al., 2001). The relatively homogenous REE patterns of eclogitic clinopyroxene contrast markedly with the wide variety of REE patterns observed in peridotitic clinopyroxene. 

Pyroxenites (as opposed to eclogites) commonly have sodium-rich aluminous augite as their clinopyroxene. Clinopyroxenes from MARID xenoliths are aluminum- and titanium-poor Mg-augites or diopsides (Dawson and Smith, 1977). 

One of the first studies to show this was performed on Kilboume Hole spinel Uierzolites (Jagoutz et al, 1980). Equihbrated neodymium isotopes in orthopyroxene and diopside defined essentially zero age isochrons, consistent with the very recent eruption age of the host volcanic rocks, while strontium isotopes were un-equilibrated. Stolz and Davies (1988) found varying degrees of equihbration between amphibole, clinopyroxene and apatite in peridotite xenoliths from S.E. Australia. Several samples contained coexisting amphibole and clinopyroxene and had almost reached isotopic equilibrium for strontium but displayed disequilibrium relations for lead and neodymium isotopes. This was taken to indicate more rapid diffusion of strontium than lead and neodymium. Some peridotite and eclogite... 

MacGregor I. D. and Carter J. L. (1970) The chemistry of clinopyroxenes and garnets of eclogite and peridotite xenoliths from the Roberts Victor Mine, South Africa. Phys. Earth Planet. Int. 3, 391-397. 

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