Eclogites mantle

Beran A, Langer K, Andmt M (1993) Single crystal infrared spectra in the range of OH fundamentals of paragenetic garnets, omphacite and kyanite in an eclogitic mantle xenohth. Mineral Petrol 48 257-268... 

Barth MG, Foley SF, Horn 1 (2002) Partial melting in Archean subduction zones constraints from experimentally determined trace element partition coefficients between eclogitic minerals and tonahtic melts under upper mantle conditions. Precamb Res 113 323-340... 

At shallow pressure (less than 1 GPa), Th becomes slightly more compatible than U in clinopyroxene (Landwehr et al. 2001) and garnet is not stable even in pyroxenite or eclogite. On the other hand, it is believed (mostly based on observations) that Pa remains more incompatible than U through the entire length of the melt column. Thus, melting at intermediate pressure should yield small °Th or U excesses, but significant Pa excess. This has been observed in the lithospheric mantle in the Colorado plateau by... 

At temperatures germane to melting and erystallizrng mantle magmas, Li isotopes do not show permil-level mass fractionation (Fig. 4 Tomascak et al. 1999b). This has since been corroborated by examination of bulk rocks and olivine separates from basaltic lavas, which yield consonant isotopic values (Chan and Frey 2003). Also, whole rocks and omphacite mineral separates from alpine eclogite with metamorphic peak temperatures approximately 650°C (Zack et al. 2003) show no consistent Li isotopic difference. 

Sulfur occurs in a variety of forms in the mantle, the major sulfur phase is monosulfide solid solution between Fe, Ni, and Cu. Recent ion microprobe measurements on sulfide inclusions from megacrysts and pyroxenite xenohths from alkali basalts and kimberlites and in diamonds gave 5 " S-values from — 11 to - - 14%c (Chaussidon et al. 1987, 1989 Eldridge et al. 1991). Sulfur isotope variations within diamonds exhibit the same characteristics as previously described for carbon i.e., eclogitic diamonds are much more variable than peridotitic diamonds. 

Eclogite A high pressure and moderate to high-temperature metamorphic rock that forms in the Earth s mantle. 

In large part, this ability of anhydrous basaltic eclogites to seismically blend into an ultramafic mantle arises from the behavior of elastic moduli in pyroxenes. In the shallowest upper mantle, orthopyroxene is —6% slow in Vp relative to olivine and about equal in Vj. However, the bulk... 

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). 

Anderson D. L. (1979) The upper mantle transition region Eclogite Geophys. Res. Lett. 6, 433-436. 

Rudnick R. L., Barth M., Horn I., and McDonough W. F. (2000) Rutile-bearing refractory eclogites missing link between continents and depleted mantle. Science 287, 278-281. 

Yaxley G. M. and Green D. H. (1998) Reactions between eclogite and peridotite mantle refertilisation by subduction of oceanic crust. Schweiz. Mineral. Petrogr. Mitt. 78, 243 -255. 

Studies of mantle xenoliths have confirmed the view from seismology that peridotite is volumetrically the dominant component of the Earth s shallow mantle (<400 km) (see Chapter 2.02). This is because xenolith suites in almost all tectonic environments are dominated by peridotites. Even at localities where other lithologies such as eclogite dominate the intact xenolith suite, mineral concentrate studies show that peridotite dominates the inventory of entrained mantle material (Schulze, 1989). Major- and trace-element studies of mineral concentrates from mined kimberlites have also been used to illustrate... 

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