Oxygen mantle

Where Af° and Ca denote atoms per 6-oxygen formula unit. These values of combined with of 360 GPa allow the ratios D olDui and DbJDi to be calculated. Typical values for mantle solidus orthopyroxenes are in the range 0.001-0.009 and 1.1-1.2, respectively. 

Hemond C, Condomines M, Fourcade S, Allegre CJ, OskarssonN, Javoy M (1988) Thorinm, strontium and oxygen isotopic geochemistry in recent tholeiites from Iceland crastal influence on mantle-derived magmas. Earth Planet Sci Lett 87 273-285... 

The major solids of Earth s mantle and crust are based on oxygen in the form of mixed oxides of various kinds (see Table 1.3). The melting and reforming of the solids that was and is continuous in the mantle could have ensured that thermodynamic equilibrium was approximately established among many of them. 

Edwards R, Sedwick PN, Morgan V, Boutron CF, Hong S (1998) Iron in ice cores from Law Dome, east Antarctica implications for past deposition of aerosol iron. Ann Glaciol 27 365-370 Filer JM (2001) Oxygen isotope variations of basaltic lavas and upper mantle rocks. Rev Mineral Geochem 43 319-364... 

Several mammals living at high altitude have bloods with high oxygen affinities. They include the llama, the golden-mantled ground squirrel... 

Qualitatively and quantitatively, compounds of silicon and oxygen are the class of substances of greatest importance in the earth s crust and mantle, in regard to both mass and variety of structural forms. 

Samples 6 and 7 in table 5.32 are from the Zabargad peridotite (Red Sea) and are representative of the chemistry of upper mantle pyroxenes (Bonatti et al., 1986). The absence of Fe203 in these samples is due to the fact that microprobe analyses do not discriminate the oxidation state of iron, which is thus always expressed as FeO. It must be noted here that the observed stoichiometry (based on four oxygen ions) is quite consistent with the theoretical formula and that no Fe is required to balance the negative charges of oxygen. 

Ballhaus, C., Berry, R.F., Green, D.H. 1990. Oxygen fugacity controls in the Earth s upper mantle. Nature, 348, 437-440. 

For geologic purposes, the dependence of the equilibrium constant K on temperature is the most important property (4). In principle, isotope fractionation factors for isotope exchange reactions are also slightly pressure-dependent because isotopic substitution makes a minute change in the molar volume of solids and liquids. Experimental studies up to 20kbar by Clayton et al. (1975) have shown that the pressure dependence for oxygen is, however, less than the limit of analytical detection. Thus, as far as it is known today, the pressure dependence seems with the exception of hydrogen to be of no importance for crustal and upper mantle environments (but see Polyakov and Kharlashina 1994). 

Harmon and Hoefs (1995) have assembled a database consisting of 2,855 O-isotope analyses of Neogene volcanic rocks worldwide. They observed a 5%c variation in the 5 0-values of fresh basalts and glasses, which they have taken as evidence of significant oxygen isotope heterogeneities in the mantle sources of the basalts. This is documented in Fig. 3.8, which plots 8 0-values vs. Mg-numbers (Harmon and Hoefs 1995). 

Thus, separate levels of the oceanic crust are simultaneously enriched and depleted in relative to normal mantle values because of reaction with sea water at different temperatures. Muehlenbachs and Clayton (1976) and Gregory and Taylor (1981) concluded that the 0 enrichments are balanced by the depletions which acts like a buffer for the oxygen isotope composition of ocean water. 

The present ocean is depleted in by at least 6%c relative to the total reservoir of oxygen in the crust and mantle. Muehlenbachs and Clayton (1976) presented a model in which the isotopic composition of ocean water is held constant by two different processes (1) low temperature weathering of oceanic crust which depletes... 

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