Three Unusual Chondrules in the Bovedy (L3) Chondrite

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Bovedy, Chondrites, L, Chondrules, Glasses, Parent Body

Scientific paper

The Bovedy (L3) chondrite [1] has recently been studied petrographically using SEM and EMPA as part of a general review of the Irish meteorites. The following chondrules are notable: Chondrule 1. A covered thin-section of the Bovedy (Sprucefield) meteorite contains a very highly-strained, ellipsoidal, radiating pyroxene chondrule with a semi-major axis of 2mm. The elongation ratio, 2.6 x, is higher than values published elsewhere [2]. Chondrule 2. A slab of Bovedy (~48 cm^2) contains an exceptionally large, ellipsoidal, porphyritic olivine chondrule (semi-major axis = 1.4 cm, minor axis = 0.8 cm). This is among the largest droplet chondrule on record [2]. The chondrule is texturally identical to other PO chondrules in the meteorite. Chondrule 3. A polished thin-section, prepared from the above slab, contains an ellipsoidal-to-irregular shaped glassy chondrule (Fig. 1). SEM and EMPA confirm a composition of pyroxenitic glass (brown) with globular and elongate inclusions of silica glass (colorless). Representative EMPA of the brown glass (in wt%) is: SiO2 57.49, Al2O3 0.93, Cr2O3 0.38, FeO 14.22, MnO 0.63, MgO 23.32, CaO 2.69, Na2O 1.03 (no other elements detected). This can be recast as a pyroxene with formula Ca(sub)0.10 Na(sub)0.07 Fe(sub)0.43Mg(sub)1.26Al(sub)0.04 Cr(sub)0.01Mn(sub)0.02Si(sub)2.08O(sub)6. The composition corresponds closely with that reported by [3] for a silica pyroxenite clast from the same meteorite. It suggests that the chondrule was derived by rapid melting of the material represented by the clast, which has been interpreted as an igneous fractionate formed in a planetary environment. References: [1] Graham A. L. et al. (1976) GCA, 40, 529-535. [2] Grossman J. N. et al. (1988) In Meteorites and the Early Solar System (J. F. Kerridge and M. S. Matthews, eds.), 619-659, Univ. Arizona. [3] Ruzicka A. and Boynton W. V. (1992) Meteoritics, 27, 283. Fig. 1, which appears here in the hard copy, shows a photograph of chondrule 3 photographed in plane polarized light. Darker areas within chondrule boundary are pyroxenitic glass. The (white) globular and elongate inclusions are silica glass. The width of the image is 1.7 mm across.

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