The UThPb age of equilibrated L chondrites and a solution to the excess radiogenic Pb problem in chondrites

U, Th, and Pb analyses of whole-rock and troilite separates from seven L chondrites suggest that the excess radiogenic Pb relative to U and the large variations in PbPb model ages commonly observed in chondritic meteorites are largely due to terrestrial Pb contamination induced prior to analyses. Using the Pb isotopic composition of troilite separates to calculate the isotopic composition of the Pb contaminants, the whole-rock data have been corrected for pre-analysis terrestrial Pb contamination. Two approaches have been used: (1) the chondrite-troilite apparent initial Pb isotopic compositions were used to approximate the mixture of indigenous intial Pb and terrestrial Pb in the whole-rock sample, and (2) a single-stage (concordant) model was applied using the assumption that the excess radiogenic Pb in these samples was terrestrial. Data for L5 and L6 chondrites yield a4551 ± 7My age using the former correction and a4550 ± 5My age using the latter one.