Mathematics – Logic
Scientific paper
Jul 2000
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2000m%26ps...35..699b&link_type=abstract
Meteoritics & Planetary Science, vol. 35, no. 4, pp. 699-706 (2000).
Mathematics
Logic
11
Scientific paper
Rumuruti chondrites (R-chondrites) constitute a new, well-established, chondrite group different to carbonaceous, ordinary, and enstatite chondrites. Many of these samples are gas-rich regolith breccias showing the typical light/dark structure and consist of abundant fragments of various parent body lithologies embedded in a fine-grained, olivine-rich matrix. Unequilibrated type 3 lithologies among these fragments have frequently been mentioned in various publications. In this study detailed mineralogical data on seven primitive fragments from the R-chondrites Dar al Gani 013 and Hughes 030 are presented. The fragments range from about 300 μm in size up to several millimeters. Generally, the main characteristics can be summarized as follows: a) Unequilibrated type 3 fragments have a well-preserved chondritic texture with a chondrule to matrix ratio of about 1:1. Chondrules and chondrule fragments are embedded in a fine-grained olivine-rich matrix. Thus, the texture is quite similar to that of type 3 carbonaceous chondrites. b) In all cases, matrix olivines in type 3 fragments have a significantly higher Fa-content (44-57 mol%) than olivines in other (equilibrated) lithologies (38-40 mol% Fa). c) Olivines and pyroxenes occurring within chondrules or as fragments are highly variable in composition (Fa0-65 and Fs0-33, respectively) and, generally, more magnesian than those found in equilibrated R-chondrites. Agglomerated material of the R-chondrite parent body (or bodies) was highly unequilibrated. It is suggested that the material that accreted to form the parent body consisted of chondrules and chondrule fragments, mainly having Mg-rich silicate constituents, and Fe-rich highly oxidized fine-grained materials. The dominating phase of this fine-grained material may have been Fa-rich olivine from the beginning. The brecciated whole rocks, the R-chondrite regolith breccias, were not significantly reheated subsequent to brecciation or during lithification, as indicated by negligible degree of equilibration between matrix components and Mg-rich olivines and pyroxenes in primitive, type 3 fragments.
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