Metasomatic processes

Thompson, J. B., Jr., 1959, Local equilibrium in metasomatic processes. In P. H. Abelson (ed.), Researches in Geochemistry, Wiley, New York, pp. 427M-57. 

There is a general agreement that the magmatism from the internal zones of Apennines has been generated in anomalous mantle sources, which have been affected by metasomatic enrichment in incompatible elements. However, the nature and timing of mantle metasomatic processes are still debated. This issue has paramount geodynamic implications and applies to all ultrapotassic magmatic provinces in Italy. 

Evidence of oxidation that may be related to metasomatic processes appears to be essentially restricted to the oxidized CV chondrites, some of the CO chondrites, and a few unequilibrated ordinary chondrites. This section will examine the evidence for these processes and will include a brief mineralogical overview of the evidence followed by a discussion of the available chemical and isotopic evidence for oxidation and metasomatism. 

Figure 8 Bulk sodium versus iron contents of oxidized and reduced CV chondrites and dark inclusions. The enrichment in sodium and iron of the oxidized group appears to be the result of metasomatic processes (sources Kallemeyn and Wasson, 1981 Kracher et ai, 1985 Bischoff et al., 1988 Palme et al., 1989 ...

Sprensen H. (1967) Metamorphic and metasomatic processes in the formation of ultramafic rocks. In Ultramafic and Related Rocks (ed. P. J. WyUie). Wiley, New York, pp. 204-212. 

The terms parent or modal metasomatism are usually used to infer the presence of minerals additional to those commonly observed in peridotites (e.g., Harte, 1983). There is a growing body of evidence indicating the addition of certainly clinopyroxene and possibly garnet to peridotites during metasomatic events (Erlank et al, 1987 Pearson et al, 2002 Shimizu, 1999 Simon et al, in press). As suggested by Erlank et al. (1987), this possibility and its implications for nomenclature should be kept in mind when discussing metasomatic processes and events. 

The Mg is also another measure of depletion, but is more susceptible to modification by secondary metasomatic processes in the mantle, or to alteration by serpentinization and/or marine weathering. Olivine Mg is sometimes used to avoid problems of grain-boundary... 

Franz L., Brey G. P., and Okrusch M. (1996b) Re-equilibration of ultramafic xenoliths from Namibia by metasomatic processes at the mantle boundary. J. Geol. 104, 599-615. 

Griffin W. L., Shee S. R., Ryan C. G., Win T. T., and Wyatt B. A. (1999c) Harzburgite to Uierzolite and back again metasomatic processes in ultramafic xenoliths from the Wesselton kimberlite. Kimberley, South Africa. Contrib. Mineral. Petrol. 134, 232-250. 

Stachel T., Viljoen K. S., Brey G., and Harris J. W. (1998) Metasomatic processes in Iherzolitic and harzburgitic domains of diamondiferous lithospheric mantle. Earth Planet. Sci. Lett. 159, 1-12. 

O Reilly S. Y. and Griffin W. L. (1988) Mantle metasomatism beneath western Victoria, Australia 1. Metasomatic processes in Cr-diopside Iherzolites. Geochim. Cosmochim. Acta 52, 433-447. 

Shallow-mantle xenoliths, hosted in alkali basalts, commonly contain C02-rich fluid inclusions (e.g., Roedder, 1965, 1984 Frey and Prinz, 1978 Murck eta/., 1978 Miller and Richter, 1982 Pasteris, 1987 Frezzotti et al., 1994 Bumard et al., 1998 Ertan and Leeman, 1999 Andersen and Neumann, 2001). In most cases, these fluid inclusions are related to metasomatic processes to which the samples were subjected. As outlined previously, the C02-rich nature of these inclusions may be a natural consequence of degassing from an ascending melt that contains both H2O and CO2, because the greater solubility of H2O in sihcate melts would allow it to remain in solution in the residual melt. Alternatively, as proposed by Andersen and Neumann (2001), the high CO2 content in these inclusions could be the result of removal of water via reactions between the original fluid and the host mineral surrounding the inclusion. 

Thompson J. B., Jr. (1987) A simple thermodynamic model for grain interfaces some insights on nucleation, rock textures, and metamorphic differentiation. In Chemical Transport in Metasomatic Processes (ed. H. C. Helgeson). Reidel, Dordrecht, pp. 169-188. 

Frei, R. Rosing, M. T. 2001. The least terrestrial leads implications for the early Archaean crustal evolution and hydrothermal-metasomatic processes in the Isua supracrustal belt (west Greenland). Chemical Geology, 181, 47-66. 

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