CHEMICAL VARIATIONS AMONG L-CHONDRITES—IV. ANALYSES,WITH PETROGRAPHIC NOTES,OF 13 L-GROUP AND 3 LL-GROUP CHONDRITES

We review our procedures for selecting, preparing and analyzing meteorite samples, present new analyses of 16 ordinary chondrites, and discuss variations of Fe, S and Si in the L-group. A tendency for Fe/Mg, S/Mg and Si/Mg to be low in L chondrites of fades d to f testifies that post-metamorphic shock melting played a significant role in the chemical diversification of the L-group. However, these ratios also vary widely and sympathetically in melt-free chondrites, indicating that much of the L-group's chemical variation arose prior to thermal metamorphism and is in that sense primary. If all L-chondrites come from one parent body, type-correlated chemical trends suggest: 1) that the body had a traditional “onion skin” structure, with metamorphic intensity increasing with depth; and 2) that it formed from material that became more homogeneous, slightly poorer in iron, and significantly richer in sulfur as accretion proceeded.