CHEMICAL VARIATIONS AMONG L‐GROUP CHONDRITES, III. MAJOR ELEMENT VARIATION IN L6 CHONDRITES

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Abstract
Bulk chemical and mineral analyses of five L6 chondrites of shock facies d to f bring the number of L6 falls analyzed by Jarosewich to 20 and enable us: 1) to examine the chemical effects of shock melting in chondrites of the same petrologic type that presumably sample a limited stratigraphic range in their parent body; and 2) to seek depth‐related chemical variations by comparing the compositions of L3 and melt‐free L6 chondrites.The mean Fe/Mg, Si/Mg, S/Mg and Ni/Mg ratios of melt‐free L6 chondrites (shock facies a to c) are virtually identical to those of L3 chondrites, suggesting that L‐group material had the same bulk composition early (L6) and late (L3) in the accretion of the parent body. Wider variations of S/Mg and Ni/Mg in L6 chondrites may signify that L6 material was less well mixed than L3, or that some mobilization of metal and troilite occurred at shock intensities (facies c) too low to melt silicates.L6 chondrites that experienced shock melting of silicates (facies d to f) show wide variations of Fe/Mg, Si/Mg, S/Mg and Ni/Mg. It appears that most of the major element variation in the L‐group is tertiary (shock‐related) rather than primary (nebular, accretionary) or secondary (metamorphic).There is some evidence that L‐group chondrites comprise two subgroups with different Fe/S ratios, but these subgroups are now poorly defined and their significance is unknown.