Trace element analysis of L and LL chondrites: Comparison of Antarctic and non-Antarctic meteorite populations

Since 1969, over 7000 meteorite fragments (representing at least 1200 separate events) have been found in Antarctica. They are important not only because of their large numbers, but also for their complement of rare and unique specimens and their long terrestrial ages (up to 10\sp6 years) compared to non-Antarctic falls (typically $\u3c$200 years). We report compositional data for mobile/volatile trace elements Au, Co, Se, Ga, Rb, Cs, Te, Bi, In, Ag, Zn, Tl and Cd in Antarctic L chondrites and both Antarctic and non-Antarctic LL chondrites. A comparison of previously obtained non-Antarctic L chondrite data to L chondrite results obtained in this work indicates that significant reason exists to doubt that the two meteorite populations derived from the same parent source. Of the 13 trace elements examined, 7 showed statistically significant differences between mildly-shocked populations; the Antarctic collection had the lower mean elemental concentration in each of those 7 cases. Two-element plots and correlation profiles also indicated significant differences between Antarctic and non-Antarctic populations. Shock-induced trace element mobilization, a major determinant of trace element contents in non-Antarctic L chondrites, plays a minor role in determining elemental abundances in Antarctic L chondrites. After ruling out alternate explanations, we believe these differences to have a preterrestrial origin and attribute them to a changing meteorite flux with time. Due to a lack of available samples, the LL chondrite study was inconclusive. Our data are consistent with previous findings which suggest Yamato Mts. and Victoria Land samples may be compositionally different. A positive correlation between trace element content and petrologic type was observed in LL chondrites. Whether this unexpected finding is due to a unique shock history of LL4 + 5 chondrites or some other explanation is unclear; more samples must be analyzed and shock facies must be obtained to further investigate this finding. Shock-induced trace element mobilization was found to be a minor factor in determining trace element content in LL chondrites