Carbon metasomatism

Ionov D. A., Dupuy C., O Reilly S., Kopylova M. G., and Genshaft Y. S. (1993b) Carbonated peridotite xenoliths from Spitsbergen implications for trace element signature of mantle carbonate metasomatism. Earth. Planet. Sci. Lett. 119, 283 -297. 

Dautria J. M., Dupuy C., Takherist D., and Dostal J. (1992) Carbonate metasomatism in the lithospheric mantle the peridotitic xenoliths from a melilititic district of the Sahara Basin. Contrib. Mineral. Petrol. Ill, 37-52. 

Blundy JD, Dalton JA (2000) Experimental comparison of trace element partitioning between clinopyroxene and melt in carbonate and silicate systems and implications for mantle metasomatism. Contrib Mineral Petrol 139 356-371... 

Taylor BE, Bucher-Nurminen K (1986) Oxygen and carbon isotope and cation geochemistry of metasomatic carbonates and fluids - Bergell aureole, Northern Italy, Geochim Cosmochim Acta 50 1267-1279... 

A topic of considerable controversy is the question of carbonate incorporation in the apatite lattice since carbonate apatite does not precipitate from aqueous solutions28, 395 398 Carbonate apatites (phosphorites) forming in marine environments134 are considered metasomatic alteration products of calcium carbonate, and as a result carbonate content decreases and phosphate content increases with time399. In biophosphates, the situation appears to be just reversed in that carbonate content increases with bone maturation and it was argued that the similarity between bone mineral and naturally occuring C03-apatite ends before it begins 397. ... 

However, it should be kept in mind that decomposition of magnetite is not a metamorphic process proper, but reflects the manifestation of carbon dioxide metasomatism, in which the introduction of corresponding amounts of CO2 from external sources is necessary. In aqueous and water-carbon dioxide fluids magnetite is quite stable in association with hematite both at low and at high temperatures (Fig. 81). Magnetite becomes unstable only at a certain CO2 content in the fluid, controlled from without, i.e. in the case of completely mobile behavior of carbon dioxide. For instance, at 227°C and Pf = 1000 bar, magnetite is stable if the CO2 content in the fluid does not exceed 35% (see Fig. 81, ). 

In the low-temperature region pyroxene and olivine can be retained only in dry rocks containing no volatiles. In the presence of a fluid phase the appearance of cummingtonite should be expected in the case of excess water, or carbonates in the case of excess carbon dioxide, which happens in hydrothermal metasomatism or even in progressive metamorphism of silicate or carbonate iron formations, respectively. 

When olivine and pyroxene are oxidized the same regularities are observed as in the oxidation of carbonates. In particular, it was established in a study of the rich and unique olivine-magnetite iron ores of the Volodarsk deposit (Ukrainian shield) that the magnesium content of the silicates increases as the magnetite content of the ore increases (Mel nik and Yaroshchuk, 1966). In this case the most likely oxidants may be water and carbon dioxide, the main components of the fluids causing metasomatic reworking of the olivine-and pyroxene-bearing iron formations. 

Devey C. W., Hemond C., and Staffers P. (2000) Metasomatic reactions between carbonated plume melts and mantle harzburgite the evidence from Friday and Domingo... 

Once formed by whatever mechanism, carbonate melts will wet an olivine and pyroxene matrix, so the melt will be interconnected and mobile at extremely low melt fraction (Hunter and McKenzie, 1989 Minarik and Watson, 1995), rendering it a potential metasomatic agent. 

Although shallow-mantle xenoliths, hosted in alkali basalts, commonly contain C02-rich fluid inclusions (see below), there have been no reports, to the author s knowledge, of H20-rich fluid inclusions in these samples. The C02-rich fluid inclusions are commonly attributed to late, possibly magma-derived, metasomatism of the samples. If such metasomatism was produced by silicate- or carbonate-rich melts, ascent of such a melt could produce saturation in a C02-rich vapor, but H2O would partition strongly into either residual melt or hydrous phases such as phlogopite or amphibole. Thus, the absence of H2O in the fluid inclusions in these samples cannot be taken as evidence that the metasomatic agent was anhydrous. 

Ionov et al. (1993a, 1996) found carbonate in spinel Iherzolite xenoliths as interstitial crystals and as aggregates with calcium-rich olivine and aluminum- and titanium-rich clinopyroxene. They interpreted the former to be primary and the latter as evidence for metasomatism by a carbonate-rich melt. Subsequently, Ionov (1998) measured trace-element abundances in the carbonates and coexisting phases, and proposed the aggregate carbonates were formed by crystal fractionation from a carbonate melt. That these carbonates represent crystallized cumulates,... 

Eaurora A., MazzuccheUi M., Rivalenti G., Vannucci R., Zanetti A., Barbieri M. A., and Cingolani C. A. (2001) Metasomatism and melting in carbonated peridotite xenoliths from the mantle wedge the Gobemador Gregores case (southern Patagonia). J. Petrol. 42, 69—87. 

Schiano P., Clocchiatti R., Shimizu N., Weis D., and Mattielh N. (1994) Cogenetic sihca-rich and carbonate-rich melts trapped in mantle minerals in Kerguelen ultramafic xenoliths implications for metasomatism in the oceanic upper mantle. Earth Planet. Sci. Lett. 123, 167—178. 

There are two common stratigraphic occurrences of chert as bedded cherts associated with shales or iron formations and as nodules in carbonate rocks (Blatt et al., 1980). The bedded cherts are predominant in Precambrian time, reaching a maximum extent 2-3 Ga, when they represented as much as 15% of the sedimentary record. The Precambrian bedded cherts contain microspheres of quartz, suggesting that they may have precipitated inorganically. Commonly, bedded cherts are associated with ophiolite sequences, which may have hydrothermal or metasomatic sources of silicate. The co-occurrence of bedded cherts and shales (typically dark in color) suggests that many cherts form in a hemi-pelagic or deep-sea, open-ocean setting, far from sources of coarse clastic material. In... 

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