Eclogites 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. 

Figure 54 Comparison of present-day osmium isotopic compositions of eclogite xenoliths from Udachnaya, Yakutia (Pearson et ah, 1995c) and S. Africa (Pearson et al, 1992 Menzies et al, 1999 Shirey et ah, 2001) with continental crust, oceanic basalts (Shirey and Walker, 1998), and Archean komatiites and basalts (Walker et al, 1989b). Udachnaya peridotite data from Pearson et al (1995a).

The Archean age of the eclogite xenolith suites that have clear crustal signatures in their elemental, stable and radiogenic isotope compositions... 

Peridotitic lithologies comprise more than 95% of the mantle lithosphere (Schulze, 1989). Thus, macrodiamonds in kimberlite are believed to come from mostly peridotitic hosts that break up during the sampling or transport that accompanies kim-berlitic volcanism. Sobolev (1974) and Hatton and Gurney (1979) noted the dichotomy that peridotite xenoliths greatly outnumber eclogite xenoliths and peridotitic silicate inclusions in diamond... 

Jacob D. and Jagoutz E. (1994) A diamond-graphite bearing eclogite xenolith from Roberts Victor (South Africa) implications for petrogenesis from Pb-, Nd-, and Sr isotopes. In Kimberlites, Related Rocks and Mantle Xenoliths (eds. H. O. A. Meyer and O. H. Leonardos) CPRM Spec. Publ. CPRM, Brasilia, vol. 1, pp. 304-317. 

Jacob D., Jagoutz E., Lowry D., and Zinngrebe E. (1998b) Comments on The origins of Yakutian Eclogite Xenoliths by G. A. Snyder L. A. Taylor G. Crozaz A. N. HaUiday B. 

Jacob D. E. and Foley S. F. (1999) Evidence for Archean ocean crust with low high field strength element signature from diamondiferous eclogite xenoliths. Lithos 48, 317-336. 

Jagoutz E. (1988) Nd and Sr systematics in an eclogite xenolith from Tanzania evidence for frozen mineral equilibria in the continental lithsphere. Geochim. Cosmochim. Acta 52, 1285-1293. 

Smith C. B., Gurney J. J., Harris J. W., Robinson D. N., Shee S. R., and Jagoutz E. (1989) Sr and Nd isotopic systematics of diamond-bearing eclogite xenoliths and eclogite inclusions in diamond from southern Africa. Kimberlites and Related Rocks. Spec. Pub. Geol. Soc. Austral., no. 14, vol. 2, pp. 853-863. 

Meyer H. O. A. and Brookins D. G. (1971) Eclogite xenoliths from Stockdale Kimberlite, Kansas. Contrib. Mineral. Petrol. 34, 60-72. 

Heaman L. M., Creaser R. A., and Cookenboo H. O. (2002) Extreme enrichment of high field strength elements in Jericho eclogite xenoliths a cryptic record of Paleoproterozoic subduction, partial melting, and metasomatism beneath the Slave craton, Canada. Geology 30, 507 -510. 

Helmstaedt H. and Schulze D. J. (1988) Eclogite-facies ultramafic xenoliths from Colorado Plateau diatreme breccias comparison with eclogites in crustal environments, evalation of the subduction hypothesis, and implications for eclogite xenoliths from diamondiferous kimberlites. In Eclogite and Eclogite Facies Rocks (ed. D. C. Smith). Elsevier, New York, pp. 387-450. 

Usui T., Nakamura E., Kobayashi K., Maruyama S., and Helmstaedt H. (2003) Fate of the subducted Farallon plate inferred from eclogite xenoliths in the Colorado Plateau. Geology 31(7), 589-592. 

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