Chemical studies of L chondrites: IV. Antarctic/non-Antarctic comparisons

Abstract

We report shock facies and RNAA data for 13 siderophile, lithophile and chalcophile volatile/mobile trace elements (Ag, Au, Bi, Cd, Co, Cs, Ga, In, Rb, Se, Te, Tl, Zn) in interior portions of 19 different L3-6 chondrites from Victoria Land, Antartica. Comparison of these data for essentially unweathered Antarctic samples with those previously published for 39 L4-6 chondrite falls indicate substantial differences. The Victoria Land population lacks the most heavily shocked (> 35 GPa) representatives found in the non-Antarctic population. While contents of nearly all trace elements studied are lower at statistically significant levels in strongly shocked (> 22 GPa) falls than in mildly shocked (> 22 GPa) ones, this is not true for the Victoria Land population. Contents of most trace elements vary with petrologic type of heavily shocked (facies d, 22–35 GPa) L chondrites from Victoria Land: such a variation is not observed for non-Antarctic falls or mildly shocked samples of either population. L4-6 chondrites from Victoria Land contain significantly lesser amounts of nearly every trace element than do falls. These differences are reflected in correlations between elements, including the putative cosmothermometric trace elements Bi, In and Tl. While Antarctic weathering could account for the compositional differences between Antarctic and non-Antarctic L chondrites, such processes cannot be responsible for the shock differences observed. Physical and chemical differences between other sorts of Antarctic and non-Antarctic meteorites suggest, rather, that the L chondrite differences are preterrestrial in origin. If so, the parent region(s) for the Victoria Land samples—that fell to earth 0.1 to 1 Myr ago—generally formed and/or evolved under higher temperature conditions than those regions yielding contemporary falls. The dominant influence of late shock that altered mobile trace element contents of L chondrites falls is not evident in samples from Victoria Land.