Clasts of lithologies that are foreign to the host rock occur in all classes of meteorites, for example, in ureilites (Prinz et al. 1987; Brearley and Prinz 1992; Bischoff et al. 2010); HED achondrites (Reid et al. 1990; Brearley and Papike 1993; Zolensky et al. 1996); ordinary chondrites (Semenko et al. 2001, 2005; Nakashima et al. 2003); carbonaceous chondrites (Olsen et al. 1988; Bischoff et al. 1993; Endress et al. 1994; Greshake et al. 2002; Jogo et al. 2011); and in ungrouped meteorites, such as the Kaidun microbreccia (Zolensky et al. 1991; Zolensky and Ivanov 2003).
A recent survey of clast-bearing meteorites revealed the presence of several distinct classes of clasts, including in over 20 different carbonaceous chondrites (Zolensky et al. 2009). The most common types of clasts in carbonaceous chondrites are fine-grained hydrous clasts (Zolensky et al. 2009). These are dark, fine-grained, and heavily aqueously altered, and are often referred to as C1 or CI clasts (e.g., Grossman et al. 1988). Some studies have suggested that they are similar to hydrous micrometeorites (Gounelle et al. 2003, 2005), but they may also just represent new lithologies that have not been previously described. Fine-grained hydrous C1 or CI clasts have previously been described in, for example, CM chondrites (Olsen et al. 1988), CH chondrites (Greshake et al. 2002), and CR chondrites (Bischoff et al. 1993; Endress et al. 1994), but also in other meteorite groups, such as in ureilites (Brearley and Prinz 1992).
A better understanding of the mineralogy and provenance of clasts in meteorites is important for several reasons. For example, they can provide clues to the genesis and origin of some classes of meteorites, such as ureilites (Brearley and Prinz 1992); they may present an opportunity to study material not yet classified or available as separate meteorites, e.g., the Kaidun microbreccia (Zolensky et al. 1991; Zolensky and Ivanov 2003); and they can offer new information on thermal and/or aqueous alteration, mixing of material, and the relative timing between these processes in the dynamic early history of the solar system (this study). Thermal and aqueous alteration, impact, and reaccretion are some of the earliest processes to have taken place in the asteroid belt (e.g., Petitat et al. 2011). The consequences of some of these processes are preserved in the carbonaceous chondrites, which are chemically the most primitive group of meteorites, but also the most highly aqueously altered (McSween 1979; Kallemeyn and Wasson 1981). Products of aqueous alteration are principally phyllosilicates, carbonates, hydrous sulfides, sulfates, and Fe-oxides (Zolensky and McSween 1988; Johnson and Prinz 1993; Zolensky et al. 1993; Brearley 2006; Lee and Ellen 2008). The mineralogy and composition of the secondary minerals, and the extent of preservation of primary phases, such as olivine, pyroxene, and Fe-Ni metal, varies with the degree of alteration (e.g., Zolensky et al. 1997; Rubin et al. 2007; Howard et al. 2009, 2011). The majority of aqueous alteration most likely occurred somewhere within asteroidal parent bodies, but the precise environment of alteration is currently poorly known (see reviews in Brearley 2003, 2006) and so analysis of clasts may provide new insights into these very early and important processes.
Aim of Study
The present paper is a detailed petrographic analysis of clasts in the CM2 carbonaceous chondrite Lonewolf Nunataks (LON) 94101. This is one of the clast-bearing meteorites that was included in the survey by Zolensky et al. (2009), who found it to have an exceptionally diverse population of clast lithologies. Here, our aim is to determine the relative timing of: (1) aqueous alteration of the clasts and the LON 94101 host, and (2) incorporation of the clasts into the LON 94101 host. In this study, we also consider the provenance of the clasts and the mechanism by which they were incorporated and mixed with their host carbonaceous chondrite.