CI chondrites

Element Solar system Mean CI chondrite, ppb Orgued, ppb Element Solar system Mean CI chondrite, ppb Orgued, ppb... 

Warren and Wasson (1979h) KREEP Warren (1989) KREEP (avg. high-K) Strength of correlation with KR KREEP/CI chondrites wt. ratio Uncertainty class (see below)... 

The concentrations of four typical moderately volatile elements—manganese, sodium, selenium, and zinc—in the various classes of chondritic meteorites are shown in Figure 12, where elements are normalized to magnesium and CI-chondrites. Again there is excellent agreement between solar abundances and Cl-meteorites. A characteristic feature of the chemistry of carbonaceous chondrites is the simultaneous depletion of sodium and manganese in all types of carbonaceous chondrites, except Cl. Ordinary and enstatite chondrites are not or only slightly... 

The compositions of the planets in the solar system and those of chondritic meteorites provide a guide to the bulk Earth composition (see Chapter 2.01). However, the rich compositional diversity of these bodies presents a problem insofar as there is no single meteorite composition that can be used to characterize the Earth. The solar system is compositionally zoned planets with lesser concentrations of volatile elements are closer to the Sun. Thus, as compared to Mercury and Jupiter, the Earth has an intermediate uncompressed density (roughly a proportional measure of metal to rock) and volatile element inventory, and is more depleted in volatile elements than CI-chondrites, the most primitive of all of the meteorites. 

Fig. 3. The photospheric/CI chondritic abundance ratios for 39 elements that are well determined for the solar photosphere. The grey-shaded region shows agreement within 10%...

Copper in meteorites is depleted in the heavier 65 isotope with respeet to the Earth (Luek et al. 2003 Russell et al. 2003). Luck et al. s (2003) study of the four main groups of carbonaceous chondrites CI-CM-CO-CV showed that Cu depletion is maximum (-1.5%o) for the C V chondrites (e.g., Allende) for which the depletion of volatile elements is strongest, which indicates that volatilization does not accormt for the observed isotopic heterogeneity (Fig. 4). Luck et al. (2003) found that 8 Cu in CI-CM-CO classes correlates with O excess, but this does not seems to be the case for CV (Luck et al. 2003) nor for the CR, CB, and the particularly Cu-depleted CH-like classes (Russell et al. 2003). In contrast, chondritic Zn is relatively heavy with 8 Zn up to 1 %o (Luck et al. 2001). The rather high 5 Zn values of iron meteorites (up to 4%o)is reminiscent of a similar fractionation of Fe isotopes between metal and silicates (Zhu et al. 2002). 

In Figure 3, aluminum is representative of refractory elements in general and the Al/Si ratios indicate the size of the refractory component relative to the major fraction of the meteorite. It is clear from this figure that the Al/Si ratio of Cl meteorites agrees best with the solar ratio, although the ratios in CM (Type 2 carbonaceous chondrites) and even OC (ordinary chondrites) are almost within the error bar of the solar ratio. The errors of the meteorite ratios are below 10%, in many cases below 5%. A very similar pattern as for aluminum would be obtained for other refractory elements (calcium, titanium, scandium, REEs, etc.), as ratios among refractory elements in meteorites are constant in all classes of chondritic meteorites, at least within —5-10%. The average Sun/CI meteorite ratio of 19 refractory lithophile elements (Al, Ca, Ti, V, Sr, Y, Zr, Nb, Ba, La, Ce, Pr, Nd, Sm, Eu, Gd, Dy, Er, Lu, see Table 2) is... 

Chemical compositions of chondrules have been determined from extracted samples using neutron activation analysis and by in situ analysis in polished sections using electron microprobe and ion probe analysis (see e.g., Gooding et al, 1980 Grossman et al, 1988 Alexander, 1995). Chondrules typically show flat refractory abundances that are relatively close to the mean chondrite value and abundances of moderately volatile elements that scatter more widely about the mean. Type II chondrules are relatively unfractionated with near-CI levels of refractories and moderately volatile elements. However, type I chondrules show systematic depletions of moderately volatile elements and a broader spread of refractory abundances with the silicon-rich type IB chondrules being poorer in refractories than the silicon-poor type IA chondrules (Figure 18). The source of the fractionations in type I chondrules is discussed below. 

A clast from Mount Padbury has a mg of 36, a molar FeO/MnO of 36, and a flat REE pattern at 9-10 X Cl chondrite abundances (Mittlefehldt, 1979)—all within the ranges for basaltic eucrites. However, many basaltic clasts are distinct in major element composition, with higher mg s and lower molar FeO/MnO ratios than those of basaltic eucrites, and have LREE-depleted patterns and (Eu/Sm)ci > 1— patterns unknown among unaltered basaltic eucrites. Some gabbro clasts are similar to cumulate eucrites in major-and trace-element contents, but many are distinct in having extreme depletions in the most incompatible elements (Mittlefehldt, 1979 Rubin and Mittlefehldt, 1992). In extreme cases, samarium abundances are only 0.02-0.03 X Cl chondrites (Rubin and Jerde, 1987 Rubin and Mittlefehldt, 1992), much less than the 1-2 X Cl typical of cumulate eucrites. These clasts have (Eu/Sm)ci of 220-260, the most extreme ratios known among solar system igneous rocks (Mittlefehldt et al., 1992). 

The small amount of the late veneer (<1% chondritic material) would not have had a measurable effect on the abundances of other elements besides HSEs, except for some chalco-phile elements, most importantly sulfur, selenium and tellurium (Figure 15(c)). The amount of sulfur presently in the Earth s mantle (200 ppm. Table 4) corresponds to only 0.37% of a nominal CI-component, while the iridium content suggests a CTcomponent of 0.67%. O Neill (1991) has, therefore, suggested that the late veneer was compositionally similar to H-chondrites which contain only 2% S (Wasson and Kallemeyn, 1988). Because H-chondrites have higher iridium (780 ppb) than Cl-chondrites, the required... 

Ehrenfreund, P., Glavin, D. P., Botta, O, et al. (2001). Extraterrestrial amino acids in Orgueil and Ivuna tracing the parent body of CI type carbonaceous chondrites. Proceedings of the National Academy of Sciences. USA. 98, 2138—41. 

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