Chondrite breccia

Primitive breccias Type-3 ordinary chondrite breccias... 

Keil K. (1982) Composition and origin of chondritic breccias. In Workshop on Lunar Breccias and Soils and their Meteoritic Analogs, LPI Technical Report 82-02 (eds. G. J. Taylor and L. L. Wilkening). The Lunar and Planetary Institute, Houston, pp. 65-83. 

Weisberg M. K., Prinz M., and Nehru C. E. (1990) The Bencubbin chondrite breccia and its relationship to CR chondrites and the ALH85085 chondrite. Meteoritics 25, 269-279. 

Chondrites contain a small fraction of chondrules that may have formed on asteroids. One rare type of chondrule (—0.1%) in type 4-6 ordinary chondrite breccias is composed largely of plagioclase (or mesostasis of plagioclase composition) and chromite (Krot et al, 1993). Krot and Rubin (1993) suggest that these chondrules may have formed by impact melting as they find impact melts with similar compositions inside shocked ordinary chondrites and such chondrules are absent in type 3 chondrites. In addition, some chromite-rich chondrules contain chromite-rich aggregates, which appear to be fragments of equilibrated chondrites. Other possible impact products were described in LL chondrites, which are mostly... 

Eugster O. and Niedermann S. (1990) Solar noble gases in the unique chondritic breccia Allan Hills 85085. Earth Planet. Sci. Lett. 101, 139-147. 

To resolve the primordial terrestrial noble gas, it would be useful to examine major noble gas reservoirs in the early solar system, which could have supplied noble gases to the Earth. As we discussed in Chapter 3, two major noble gas components occur very widely in the solar system and can be a potential source for the terrestrial noble gas. They are solar noble gas (representative of the sun), which is generally assumed to be best represented by solar wind noble gas implanted on Al-foil target plates on the moon (elemental ratio) and on lunar breccia (isotopic ratio) (e.g., Ozima et al., 1998), and Q phase noble gas (see Wieler, 1994, for a review), which occurs very widely in various chondrites. Next we will compare the bulk Earth noble gas, which we assume to be represented by atmospheric noble gas with these two major noble gas components in the solar system. 

Bell, J. F. Keil, K. (1988) Spectral alteration effects in chondritic gas-rich breccias implications for S-class and Q-class asteroids. Proc. 19th Lunar Planet. Sci. 

Rubin A. E. and Scott E. R. D. (1997) Abee and related EH chondrite impact-melt breccias. Geochim. Cosmcohim. Acta 61, 425-435. 

An additional problem with the division into six petrologic types is that it ignores the role played by impacts in modifying and mixing chondritic material. Many chondrites are breccias of materials with diverse alteration or metamorphic histories. Thus the petrologic type may provide no information about the metamorphic history of the whole chondrite, only an approximate guide to the history of most constituents. 

Source Based largely on lists in Grady (2000) with additional data from Krot et al. (2002a) for CR, CH, and CB and Kallemeyn et al. (1996) and Bischoff (2000) for R chondrites. A small number of chondrites that are classified as intermediate types (e.g., 3-4, 4-5, etc.) and mixed breccias (e.g., type 3-5) were omitted except for the R chondrites, which are mostly breccias of type 3-5 or 3-6 material. Numbers of H, L, and LL chondrites have not been corrected for probable pairings the number of individual meteorites is probably —2-4 X smaller than the number of specimens. 

Advocates for impact heating of chondrites point to Portales Valley, a breccia of H6 clasts embedded in a matrix of once-molten metallic Fe,Ni, which cooled slowly to form a Widmanstatten pattern (Rubin et al, 2001). Gaffey and Gilbert (1998) suggest that molten metal on the H parent body was derived from impact-formed melt sheets or residues of metal-rich projectiles and that the HE irons were also derived from this melt. However, the origin of Portales Valley and the link with HE irons remain obscure as asteroids are thought to be too small for impacts to generate melt sheets (Keil et al, 1997). 

The mineralogy of CV3 chondrite matrices prior to alteration is not clear. The two reduced CV3 chondrites that have been studied by TEM are not ideal samples. In Leoville, which is moderately shocked, Nakamura et al (1992) found aggregates of rounded, 10-100 nm olivine grains with interstitial amorphous material, but attributed this to shock. In Vigarano, which is a breccia of altered and unaltered material... 

The unique chondrite, Kaidun, appears to be a breccia composed almost entirely of millimeter and submillimeter sized fragments of diverse kinds of chondrites (Zolensky and Ivanov, 2001). Kaidun may be a clast-rich, chondrule-poor chondrite that formed in a nebula region where chondrules were much rarer than clasts (Scott, 2002). Cl chondrites and the Tagish Lake chondrite also appear to have formed from sub-millimeter particles of altered chondritic material (Nakamura et al., 2003). Thus disagregation of early-formed planetesimals may have been widespread. 

Nakamura T., Noguchi T., Zolensky M. E., and Tanaka M. (2003) Mineralogy and noble-gas signatures of the carbonate-rich lithology of the Tagish Lake carbonaceous chondrite evidence for an accretionary breccia. Earth Planet. Sci. Lett. 207, 83-101. 

Rubin A. E., Ulff-M0ller F., Wasson J. T., and Carlson W. D. (2001) The Portales Valley meteorite breccia evidence for impact-induced melting and metamorphism of an ordinary chondrite. Geochim. Cosmochim. Acta 65, 323-342. 

Rubin A. E., Zolensky M. E., and Bodnar R. J. (2002) The halite-bearing Zag and Monahans (1998) meteorite breccias shock metamorphism, thermal metamorphism and aqueous alteration on the H-chondrite parent body. Meteorit. Planet. Sci. 37, 124-141. 

The Cl chondrites represent one of the most curious paradoxes of cosmochemistry. Despite their unfractionated compositions, the Cl chondrites are the most altered of all chondrites, with water contents of —19.5 wt.% (Nagy et al., 1963). Anhydrous phases (olivines and pyroxenes) represent less than 1 vol.% of these meteorites (Leshin et al., 1997). Cl chondrites are complex meteorites that consist of a dark, fine-grained matrix comprised of phyllosilicates with magnetite, sulfides, carbonates, and sulfates embedded within it (e.g., DuFresne and Anders, 1962 Nagy, 1966). They have experienced extensive breccia-tion on their asteroidal parent bodies that caused... 

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