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HED Meteorites

Category: Meteorite Wiki
Posted: 12-20-2013 16:30
Views: 1250
Synopsis: describe HED group Howardites, eucrites, and diogenites are genetically re-lated and form the HED suite of achondrites, which may come from Vesta. Eucrites and diogenites are magmatic rocks, representing a wide range of chemical compositions and variable crystallization histories. At least 85% of HED meteorites are impact breccias formed in the regolith and megaregolith of their parent body. The megaregolith is the thick layer of fractured and possibly mixed planetary crust beneath the surface regolith, which has been discussed in detail by Hartmann (1973, 1980). While many eucrites and diogenites occur as monomict breccias, howardites are mechanical mixtures of diogenites and eucrites and, hence, breccias by definition (e.g., McCarthy et al., 1972; Duke and Silver, 1967; Bunch, 1975; Delaney et al., 1983; Buchanan and Reid, 1996). In the order of increasing amounts of di- ogenite component, polymict HED breccias are classified as polymict eucrites, howardites, and polymict diogenites ( Delaney et al., 1983). According to Delaney et al. (1983), eucrites containing up to 10% diogenitic material are called polymict eucrites, whereas diogenites containing up to 10% eucritic material are called polymict diogenites. HED me- teorites containing 10–90% eucritic material are defined as howardites. Several members of the HED suite display pet- rologic features that seem to result from annealing by igne- ous activity or impact-melt sheets after crystallization and brecciation (e.g., Labotka and Papike, 1980; Takeda et al., 1981; Yamaguchi and Takeda, 1994, 1995; Yamaguchi et al., 1994, 1997; Metzler et al., 1995; Buchanan and Reid, 1996; Takeda, 1997; Mittlefehldt et al., 1998; Saiki and Takeda, 1999)

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