STUDY ON CHEMICAL COMPOSITIONS OF 19 L AND LL CHONDRITES AND ITS APPLICATION IN TAXONOMY

Abstract

Reported in this paper are precise INAA data on 19 L and LL chondrites (7 Chinese chondrites and 12 from other countries). The L and LL chondrite data normalized to Mg and to CI chondrite indicate that for several lithophiles (V, Al, Cr and Mn), the extent of scatter is low, similar to that observed in carbonaceous chondrites. The average concentration of siderophiles in the LL group is lower than that in the L group. On the basis of olivine composition and atomic ratio (Ir/Au), we reclassify the five previously labeled L ehondrites as LL members. The atomic ratios of Ir/Au in the LL chondrites are lower than those in the L chondrites (the division is set at an Ir/Au ratio of 2.5). The atomic ratio of Ir/Au appears to be a useful classification parameter for ordinary chondrites. Therefore, it can be considered as a new taxonomic parameter. Of the elements studied, Br, a high volatile, seems most likely to show thermometamorphic effects, depending on petrologic types. The concentration of bromine and the atomic ratio of Br/Se are0.5 μg/g and0.05 for types 3 and 4, and 0.5 μg/g and0.05 for types 5 and 6, respectively.