Melting xenolith

Blatter DL, Carmichael ISE (1998) Hornblende peridotite xenoliths from central Mexico reveal the highly oxidized nature of subarc upper mantle. Geology 26 1035-1038 Blundy J, Wood B (2003) Mineral-melt partitioning of uranium, thorium and their daughters. Rev Mineral Geochem 52 59-123... 

Piccardo G. B. and Ottonello G. (1978). Partial melting effects on coexisting mineral compositions in upper mantle xenoliths from Assab (Ethiopia). Rend. S.I.M.P, 34 499-526. Pitzer K. S. (1973). Thermodynamics of electrolytes. I Theoretical basis and general equations. J. Phys. Chem., 77 268-277. 

Figure 4-20 Falling velocity of a mantle xenolith (density 3200 kg/ m ) in a basaltic melt (density 2700km/m ) for viscosity of IPa-s and 100 Pa s. The calculation does not continue to greater sizes because the applicability of the formulation is limited to Re <3 X 10 . At small radius, the velocity is proportional to the square of the radius (Stokes law). For larger radius, the velocity does not increase so rapidly with radius, and roughly increases with square root of radius.

Melting and dissolution kinetics application to partial melting and dissolution of xenoliths. /. Geophys. Res. 91, 9395-9406. 

Figure 4-19 Plagioclase phase diagram and plagioclase melting Figure 4-20 Free falling velocity of a mantle xenolith in a basalt Figure 4-21 Sketch of boundary layer, and boundary layer thickness Figure 4-22 MgO diffusion profile in olivine and in melt during olivine growth...

Alicudi rocks, like other Aeolian volcanics, contain a variety of meta-morphic and magmatic xenoliths. Metamorphic xenoliths are represented by predominant quartz-rich rocks displaying evidence of partial melting along grain boundaries, and by a few biotite gneiss and granulite... 

De Astis et al. (2000) and Calanchi et al. (2002b) noticed that calc-alkaline and HKCA basalts at Vulcano and Panarea have distinct trace element ratios (e.g. La/U, Rb/Zr, Zr/Nb) compared to the associated sho-shonitic and KS mafic volcanics. However, the rocks of the Calabro-Peloritano basement underlying the Aeolian volcanoes show compositions that resemble the calc-alkaline rather than shoshonitic and KS rocks this was interpreted to exclude a derivation of potassic rocks from calc-alkaline parents via crustal assimilation. The same conclusion was drawn by Frez-zotti et al. (2004), who modelled magma contamination processes using melt inclusions entrapped in metamorphic xenoliths as contaminants. 

In contrast, Esperanca and Crisci (1995) and Trua et al. (1998) propose that magmatism in the Sicily Province is derived from young lithosphere that was enriched by addition of asthenosphere-derived melts. As recalled earlier, this is a relatively young process, which occurred during Permian-Triassic times. The young age of metasomatism is supported by Sr-Nd isotopic studies on the Iblei xenoliths, which give a pseudo-isochron of about 200 Ma (Tonarini et al. 1996). 

Frezzotti ML, Peccerillo A, Bonelli R (2003) Magma ascent rates and depths of crustal magma reservoirs beneath the Aeolian volcanic arc (Italy) inferences from fluid and melt inclusions in xenoliths. In De Vivo B, Bodnar RJ (eds) Melt Inclusions in Volcanic Systems Methods, Applications and Problems. Elsevier, Amsterdam, pp 185-205... 

Frezzotti ML, Zanon V, Peccerillo A, Nikogossian I (2004b) Silica-rich melts in quartz xenoliths from Vulcano island and their bearing on processes of crustal anatexis and crust-magma interaction beneath the Aeolian Arc, southern Italy. J Petrol 45 3-26... 

Along with studies of melt inclusions, the study of mantle xenoliths (samples of mantle material entrained and brought to the surface in eruption magmas) and exhumed mantle rocks is one of the most common applications of SIMS for trace element analysis. SIMS is ideally suited to this task, as there is no need to try to make mineral separates from what are often limited amounts of sample, alteration can be prevented, and zoning easily studied. 

Lithic fragments Xenolithic—clasts of different chemical class to host Cognate—impact melt fragments... 

In detail, however, the picture is not so simple. All mantle peridotites (whether massive peridotites or xenoliths) are metamorphic rocks that have had a complex subsolidus history after melt extraction ceased. As well as subsolidus recrystallization, peridotites have undergone enormous amounts of strain during their emplacement in the lithosphere. Massive peridotites show modal heterogeneity on the scale of centimeters to meters, caused by segregation of the chromium-diopside suite of dikes, which are then folded back into the peridotite as deformation continues. The net result is more or less diffuse layers or bands in the peridotite, which may be either enriched or depleted in the material of the chromium-diopside suite, i.e., in climopyroxene and orthopyroxene in various proportions, minor spinel, and sulfide. This process should cause approximately linear correlations of elements versus MgO, broadly similar to, but not identical with, those caused by melt extraction. Indeed, there is... 

While all spinel-lherzolite facies suites show remarkably similar compositional trends as a function of depletion, some garnet peridotite xenoliths in kimberlites and lamproites from ancient cratonic lithospheric keels show signih-cantly different trends (e.g., see Boyd, 1989 Chapters 2.05 and 2.08). Most of these xenoliths are extremely depleted extrapolation of the trends back to the PM MgO of 36.7% gives similar concentrations of Si02, EeO AI2O3, and CaO to the spinel Iherzolites (O Neill and Palme, 1998) the difference in their chemistry is due to a different style of melt extraction, and not a difference in original mantle composition. 

Figure 8 Abundances of RLEs in fertile spinel-UierzoUte xenoliths from various occurrences. Compatible elements bave constant enrichment factors. Abundances decrease with increasing degree of incom-patibiUty, reflecting removal of very small degrees of partial melts (after Jochum et al., 1989).

The late veneer hypothesis has gained additional support from the analyses of the osmium isotopic composition of mantle rocks. Meisel et al. (1996) determined the Os/ Os ratios of a suite of mantle xenoliths. Since rhenium is more incompatible during mantle partial melting than osmium, the Re/Os ratio in the mantle residue is lower and in the melt higher than the PM ratio. By extrapolating observed trends of Os/ Os versus AI2O3 and lutetium, two proxies for rhenium, Meisel et al. (1996) determined a Os/ Os ratio of 0.1296 0.0008 for the primitive mantle. This ratio is 2.7% above that of carbonaceous... 

Osmium isotopes currently provide the strongest case for mineral-to-mineral disequilibrium, and for mineral-melt disequilibrium available from observations on natural rocks. Thus, both osmium alloys and sulfides from ophiolites and mantle xenoliths have yielded strongly heterogeneous osmium isotope ratios (Alard et al., 2002 Meibom et al., 2002). The most remarkable aspect of these results is that these ophiolites were emplaced in Phanerozoic times, yet they contain osmiumbearing phases that have retained model ages in excess of 2 Ga in some cases. The melts that were extracted from these ophiolitic peridotites contained almost certainly much more radiogenic osmium and could, in any case, not have been in osmium-isotopic equilibrium with all of these isotopically diverse residual phases. 

Peridotite fertilization may also result from the fractional solidihcation of exotic (deep-seated) melts inhltrated in wall rocks of translithospheric magma conduits. This process was hrst described in composite mantle xenoliths (Wilshire and Shervais, 1975 Gurney and Harte, 1980 Irving, 1980 Wilshire et al., 1980 Boivin, 1982 Harte, 1983 Harte et al, 1993 Menzies et ah, 1987), where it is referred to as modal metasomatism when new (generally hydrous) minerals are precipitated (Dawson, 1984 Kempton, 1987), or Fe-Ti metasomatism (Menzies et al., 1987) when the attention is focused on chemical enrichment. In contrast with ultramafic xenoliths, the tectonically emplaced and oceanic peridotites contain only sparse rock types attributable to mantle metasomatism by deep-seated melts. Examples of wall-rock, modal, and Fe-Ti metasomatism were nevertheless described in IP orogenic Iherzolites, notably in the Pyrenees (Fabrics et al., 1989 Bodinier et al., 1988, 1990, 2003 McPherson et al., 1996 Woodland et al., 1996). 

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