Chondrites ordinary

H, L, and LL chondrites. Ordinary chondrites (Figure 13(b)) are characterized by (i) magnesium-normalized refractory lithophile abundances —0.85 X Cl chondrites (Figure 2) ... 

Other meteorite classes like C2, CO and ordinary chondrites contain much smaller inclusions less than 1 mm (MacPherson et al. 1988) and require ion microprobe techniques to evaluate the isotopic compositions. On the least metamorphosed side. Cl have very few inclusions or oxide grains, but are the carrier of the greatest amounts of stellar nanodiamond and other carbides (Anders and Zirmer 1993). As will be shown for Cr anomalies in carbonaceous chondrites, the survival of the mineral carriers of the anomalies also depends on the metamorphic grade of the meteorites. Nevertheless, isotopic anomalies have also been formd in higher metamorphic grade from other classes, especially in the reduced enstatite chondrites. 

Figure 8. Figure (a) after Clayton et al. (1976, 1977). The scales are as in Figure 1. The O isotopic compositions of the different meteorite classes are represented ordinary chondrites (H, L, LL), enstatite chondrites (EFl, EL), differentiated meteorites (eucrites, lAB irons, SNCs) and some components of the carbonaceous chondrites. As the different areas do not overlap, a classification of the meteorites can be drawn based on O isotopes. Cr (b) and Mo (c) isotope compositions obtained by stepwise dissolution of the Cl carbonaceous chondrite Orgueil (Rotaru et al. 1992 Dauphas et al. 2002), are plotted as deviations relative to the terrestrial composition in 8 units. Isotopes are labeled according to their primary nucleosynthetic sources. ExpSi is for explosive Si burning and n-eq is for neutron-rich nuclear statistical equilibrium. The open squares represent a HNOj 4 N leachate at room temperature. The filled square correspond to the dissolution of the main silicate phase in a HCl-EIF mix. The M pattern for Mo in the silicates is similar to the s-process component found in micron-size SiC presolar grains as shown in Figure 7.

In ordinary chondrites, Ca-Al rich inclusions are also present and give the canonical value (Russell et al. 1996), but other object like chondrules or mineral grains give reduced values by a factor of 5 to 100 (Hinton and Bischoff 1984 Hutcheon and Hutchison 1989). Delayed formation relative to CAIs is a probable cause. High precision ICPMS measurements of Mg have been used to address the timing of chondrule formation and show the importance of gas during the formation process (Galy et al. 2000). 

As Sm, Nb can be used to place constraints on the site of p-process nucleosynthesis. After a first hint (Harper 1996 Sardoup et al. 2000), its presence was established in an ordinary chondrite and a mesosiderite (Fig. 9f Schonbachler et al. 2002). The solar system initial Nb/ Nb ratio was between 10 and 3x10 a value in the same order of magnitude as most of the other extinct radioactivities. 

Busfield A, Gilmour JD, Whitby JA, Turner G (2004) Iodine-xenon analysis of ordinary chondrite halide implications for early solar system water. Geochim Cosmochim Acta 68 195-202 Busso M, Gallino R, Wasserburg GJ (1999) Nucleosynthesis in asymptotic giant branch stars relevance for galactic enrichment and solar system formation. Annu Rev Astronom Astrophys 37 239-309 Cameron AGW (1969) Physical conditions in the primitive solar nebula. In Meteorite Research. Millman PM (ed) Reidel, Dordrecht, p 7-12... 

Choi BG, Huss GR, Wasserburg GJ, Gallino R (1998) Presolar corundum and spinel in ordinary chondrites origins from AGB stars and a supernova. Science 282 1284-1289 Christophe M (1968) Un chondre exceptionnel dans la meteorite de Vigarano. Bui Soc Er Mineral Cristallogr 91 212-214... 

Gooding JL, Mayeda TK, Clayton RN, Fukuoka T (1983) Oxygen isotopic heterogeneities, their petrological correlations, and implications for melt origins of chondrules in unequilibrated ordinary chondrites. Earth Planet Sci Lett 65 209-224... 

Gopel C, Manhes G, Allegre CJ (1994) U-Ph systematics of phosphates from equilibrated ordinary chondrites. Earth Planet Sci Lett 121 153-171... 

Hidaka H, Ohta Y, Yoneda S, DeLaeter JR (2001) Isotopic search for live Cs in the early solar system and possibility of Cs- Ba chronometer. Earth Planet Sci Lett 193 459-466 Hinton RW, Bischofif A (1984) Ion microprobe magnesium isotope analysis of plagioclase and hibonite from ordinary chondrites. Nature 308 169-172... 

Huss GR, MacPherson GJ, Wasserburg GJ, Russell SS, Srinivasan G (2001) Aluminum-26 in calcium-aluminum-rich inclusions and chondrales from unequilibrated ordinary chondrites. Meteorit Planet Sci... 

Hutcheon ID, Steele IM, Wachel DES, MacDougall JD, Phinney D (1983) Extreme Mg fractionation and evidence of Ti isotopic variations in Murchison refractory inclusions. Lunar Planet Sci XIV 339-340 Hutcheon ID, Hutchison R (1989) Evidence from the Semarkona ordinary chondrite for A1 heating of small planets. Nature 337 238-241... 

Chondrules from Chainpur LL3 meteorite have somewhat lower 5 Mg values than Chainpur LL3 matrix. Cl, and terrestrial mantle clinopyroxene. Chondrules from the Bjurbole L/LL4 ordinary chondrite also have slightly lower 8 Mg values than Cl and LL3 matrix. Chondrules, matrix, and whole rock samples from the Allende CV3 meteorite span a larger range in 5 Mg that overlaps the Cl and ordinary chondrite data. 

Variability in Mg isotope ratios among chondritic meteorites and their constituents is dominated by mixing between a radiogenic CAI-like reservoir and a reservoir resembling ordinary chondrites. The mixing is evident in 5 Mg and 8 Mg, Al/Mg, and A 0 values but... 

Clayton RN, Mayeda TK, Goswami JN, Olsen EJ (1991) Oxygen isotope studies of ordinary chondrites. Geochim Cosmochim Acta 55 2317-2337... 

The Ca isotope ratios of meteoritic samples are of interest because they can give information on early solar system processes and because meteorites represent the materials from which the Earth accreted and hence relate to the expected values for the bulk Earth. Russell et al. (1978b) made the first measurements of stable Ca isotope variations in meteorites. They formd variations of about +l%o for the Ca/ Ca ratio in samples from six different meteorites. Although some of these samples were spiked after having separated the Ca with an ion exchange column and hence may contain artifacts, it is clear from their data that bulk meteorites have some variability in 8 Ca and that the average value is quite close to the terrestrial standard. No data on bulk meteorites have been reported since the Russell et al. (1978b) measurements, and since their one measurement of an ordinary chondrite had a poor Ca column yield, there exist no reliable measurements that can be used to verify the composition of typical chondritic meteorites. 

The temperature of 50% condensation of a given element in the Solar Nebula defined by Wasson (1985) is 1037 K for Cu and 660 K for Zn. The much more volatile character of Zn with respect to Cu conditions the relative abundances of the two elements among the dififerent classes of chondrites. Copper concentrations vary from 80 to 120 ppm in carbonaceous and ordinary chondrites (Newsom 1995). In contrast, Zn concentrations decrease from 310 ppm in the volatile-rich Cl to 100 ppm in CO and CV, and to 50 ppm in ordinary chondrites. McDonough and Sun (1995) estimate the Cu and Zn content of the Bulk Silicate Earth to be 30 and 55 ppm, respectively. 

Robert F, Epstein S (1982) The concentration and isotopic composition of hydrogen, carbon and nitrogen carbonaceous meteorites. Geochim Cosmochim Acta 46 81-95 Robert F, Merlivat L, Javoy M (1978) Water and deuterium content in ordinary chondrites. Mete-oritics 12 349-354... 

The characteristics of the presolar diamonds also change with the metamorphic grade of the host meteorite. F igure 5.15 shows the typical bimodal release of heavy noble gases (here illustrated by xenon) in Orgueil, an unheated chondrite. This pattern is compared to the xenon-release patterns of two ordinary chondrites that have experienced different degrees of mild metamorphism. The amount of low-temperature gas, labeled P3 for historical reasons, is a sensitive function of temperature. Its abundance correlates well with other indicators of... 

Components of chondrites, (a) Photomicrograph of porphyritic chondrule showing olivine crystals in glassy mesostasis (dark), in the Clovis ordinary chondrite, field of view (FOV) 1.8 mm. 

The acapulcoites (Fig. 6.7a) have recrystallized textures, but a few relict chondrules have been reported (McCoy et al., 1997a). The relative proportions of the minerals (olivine, orthopyroxene, diopside, plagioclase, metal) in acapulcoites are similar to those in ordinary chondrites, and the abundances of the major elements are nearly chondritic. However,... 

Grossman, J. N. and Brearley, A. J. (2005) The onset of metamorphism in ordinary and carbonaceous chondrites. Meteoritics and Planetary Science, 40, 87-122. 

Stoffler, D., Keil, K. and Scott, E. R. D. (1991) Shock metamorphism of ordinary chondrites. Geochimica et Cosmochimica Acta, 55, 3845-3867. 

Wlotzka, F. (1993) A weathering scale for the ordinary chondrites. Meteoritics, 28, 460. 

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