Mantle carbon content

Trull, T., Nadeau, S., Pineau, F., Polve, M., Javoy, M. (1993) C-He systematics in hotspot xenoliths Implications for mantle carbon contents and carbon recycling. Earth Planet. Sci. Lett., 118, 43-64. 

Trail TW, Nadeau S, Pineau F, Polve M, Javoy M (1993) C-He systematies in hotspot xenoliths implications for mantle carbon contents and carbon recycling. Earth Planet Sci Lett 118 43-64 Turcotte DL, Schubert G (1988) Tectonic implications of radiogenic noble gases in planetary atmospheres. Icarus 74 36-46... 

Holloway J. R. (1998) Graphite-melt equilibria during mantle melting constraints on CO2 in MORB magmas and the carbon content of the mantle. Chem. Geol. 147, 89-97. 

Estimates of the carbon content of the Earth indicate that it too is a major component of the Earth s volatile budget. Tingle (1998) estimated that the primordial carbon content of the Earth was between 1024 and 1025 g. This is many orders of magnitude greater than the total carbon at the Earth s surface, and even allowing for carbon stored in the Earth s core implies that the mantle is a huge carbon reservoir. Precisely locating this carbon, however, is more difficult and this topic is discussed more fully in Chapter 5, Section 5.1.2. 

A first-order minimum estimate of the mass of carbon in the mantle can be made by assuming that the MORB-source is typical of the mantle as whole, and that it contains 20 ppm C, in keeping with the new results on low carbon in the MORB source and the low content of carbon in mantle minerals. In this case the mantle contains 8.6 x 1022 g (86 X 106 Gt) of carbon. This estimate is smaller than, but of the same order of magnitude as, that of Zhang and Zindler (1993) who used C/3He ratios to estimate the carbon content of the degassed mantle reservoir as 22 x 1022g (1.8 x 1022 mol). 

Natural occurrence. Carbon monoxide is produced during the incomplete combustion of carbon and carbon-containing compounds, hence it occurs in the exhaust of internal-combustion engines, in coal stoves, furnaces, and gas appliances functioning with an oxygen deficiency. Carbon monoxide is also naturally present in the atmosphere, chiefly as a product of volcanic activity. It occurs dissolved in molten volcanic rock at high pressures in the Earth s mantle. Carbon monoxide contents of volcanic gases vary from less than 1000 ppm vol. to as much as 2 vol.%. It also occurs naturally in bushfires. 

Extensive, horizontal sandstone plateaus occur in tropical shield areas. Well-known examples are the Precambrian Roraima sandstone formations on the Guiana Shield and the Voltaian sandstone formations in Western Africa. Major occurrences of consolidated sands are found in Northern Africa, in Guyana and Surinam, eastern Peru, northeastern Brazil and in Liberia (western Africa). These sandstone formations have a history of tropical weathering in common they all have a deep weathering mantle of bleached, white sands that are very rich in quartz, poor in clay and excessively drained. Electrolyte contents differ by region In arid and semi-arid areas where evaporation exceeds precipitation, salts and carbonates may accumulate at or near the surface of the soil. 

Oxide minerals, e.g. Fe3+ ions and carbonate and seawater contents Deep zones of metals and very reduced minerals in the mantle Some parts of the atmosphere 03, N2/02 All such chemicals are thermodynamically unstable in the absence of air relative to C02, CH4 and H20 and in air all are unstable relative to C02 and H20 but all have considerable kinetic stability... 

CO2 is the second most abundant gas species in magmatic systems. In a survey of CO2 emanations from tectonically active areas worldwide, Barnes et al. (1978) attributed 8 C-values between -8 and -4%c to a mantle source. This is, however, problematic, because average crustal and mantle isotope compositions are more or less identical and surflcial processes that can modify the carbon isotope composition are numerous. A more promising approach may be to analyze the C-content of CO2 collected directly from magmas at high temperatures. 

From available, though approximate, estimates, about 1023 g of carbon-containing gases are concentrated in the rocks of the Earth s crust and mantle (lithosphere) (Korstenshtein, 1984 Sokolov, 1971). This mass of carbon exceeds by approximately 104 times the amount present today in the biosphere (over the Earth surface). Between the biosphere and lithosphere there is a constant, very intensive exchange of carbon that is self-regulatory. From the data of Barenbaum (2000, 2002), due to the Le Chatelier principle (Krapivin et al., 1982), the content of mobile carbon in the system tries to attain a stable relationship ... 

Small Quantities. Wear nitrile rubber gloves, laboratory coat, and eye protection. Work in the fume hood. Small quantities of hexamethylphosphoramide can be hydrolyzed with concentrated hydrochloric acid under reflux for at least 5 hours. Add 215 mL of concentrated hydrochloric acid to a 500-mL, three-necked, round-bottom flask equipped with stirrer, heating mantle, water-cooled condenser, and dropping funnel. Over a period of about 30 minutes, add 50 mL (51.5 g, 0.3 mol) of the hexamethylphosphoramide through the dropping funnel while refluxing the reaction mixture. After addition is complete, reflux the mixture for at least 5 hours. Cool the contents of the flask, neutralize carefully with dilute sodium hydroxide or sodium carbonate, and wash the resultant mixture into the drain.6... 

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