Chondrite clans

Krot A. N., Meibom A., Weisberg M. K., and Keil K. (2002a) The CR chondrite clan implications for early solar system processes. Mcrconr. Planet. Sci. 37, 1451-1490. 

Chondrites are classified into five major groups based on properties such as bulk composition, petrography, and oxygen isotopic ratios (Brearley Jones 1998). They are further subdivided into several clans within these major types... 

Adelaide is an ungrouped, type-3 carbonaceous chondrite with affinities to the CM-CO clan, but appears to have escaped the thermal metamorphism and alteration commonly observed in the CM and CO carbonaceous chondrites (Fitzgerald and Jones, 1977 Davy et al., 1978 Kallemeyn and Wasson, 1982 Hutcheon and Steele, 1982 Kerridge, 1985 Brearley, 1991 Huss and Hutcheon, 1992 Kiotetal., 2001b,c). 

Krot A. N., Brearley A. J., Petaev M. I., Kallemeyn G. W., Sears D.W. G., Benoit P. H., Hutcheonl. D., Zolensky M.E., and Keil K. (2000d) Evidence for in situ growth of fayalite and hedenbergite in MacAlpine Hills 88107, ungrouped carbonaceous chondrite related to CM-CO clan. Meteorit. Planet. Sci. 35, 1365-1387. 

The major difficulty with closed-system models is that they do not explain why some chondrules are olivine-rich and others are pyroxene-rich. It is very difficult to see how fine-grained nebula dust could have been sorted into high Mg/Si dustballs for olivine chondrules and low Mg/Si dustballs for pyroxene-rich chondrules (e.g.. Wood, 1996a). Although matrix contains both phases, they are not segregated into chondrule-sized volumes. The only plausible way to produce both olivine-rich and pyroxene-rich chondrules is by high-temperature reactions between condensed material and nebular gas. New evidence, especially from CR-CH-CB clan chondrites, supports this thesis. 

CR clan chondrites. The CR clan includes a wide diversity of chondritic meteorites that share sufficient mineralogic and isotopic properties in common to be considered genetically related (Weisberg et al, 1995) it includes the CR and... 

The acapulcoite-lodranite clan is the prototypical primitive achondrite group. The acapulcoites have modal mineral abundances very much like those of ordinary chondrites, relict chondrules are reported from a few, and their bulk compositions are broadly chondritic (McCoy etal.,l 996 Mittlefehldt et al., 1996, 1998). The lodranites are distinctly nonchondritic. They are generally depleted in... 

Figure 4 Cl-normalized lithophile element ratios in acapulcoite-lodranite clan (ale), winonaite-IAB-iron silicate inclusion clan (wic) and some unique meteorites showing the effects of melting in the silicate-oxide system. Residual silicate source regions will have low Na/Sc and Sm/Sc, while mafic melts will have the opposite characteristics. Many acapulcoite-lodranite clan and winonaite-IAB-iron silicate inclusion clan meteorites have essentially chondritic lithophile element ratios. Data from sources listed in the text, except for Divnoe (Petaev et al., 1994 Weigel et al., 1997), and Enon (Kallemeyn and Wasson, 1985).

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