Properties and mixing of soil components in Apollo 17 double-drive tube 79001/2

Abstract— Previous studies of Apollo 17 double-drive tube 79001/2 showed that portions of this lunar regolith segment have some unusual properties, such as very high I_s/FeO values (Monis et al., 1989) and N contents (Stone and Clayton, 1989). To understand the geologic significance of these features in this core, we determined the grain-size distribution and modal abundance of the petrographic constituents for samples from 12 different depths of the core. Also, we measured the elemental and isotopic compositions of noble gases in the coarse-grained (150–250 μm) and fine-grained (<20 μm) sample fractions from four depths of this core. The agglutinate abundance and ³⁶Ar contents show depth-related variations similar to those observed for I_s/FeO and N in this core. Samples from the top (～0.5 cm depth) and the bottom (～45 cm depth) of the drive tube are related to Apollo 17 submature soils with about 250–300 Ma galactic cosmic-ray (GCR) exposure age. But the soil at the top of the drive tube received additional surface irradiation for ～2 Ma after deposition at Van Serg. The samples at intermediate depths (i.e., ～7 cm (upper zone) and ～20 cm (lower zone) of the 79001/2 core) show features characteristic of mixtures of Apollo 17 mature soils and finely comminuted regolith breccias having about 600–800 Ma GCR exposure age. The mixing ratios between the coarse and fine fractions of the intermediate-depth samples are similar to each other. Though the mixing ratios for the samples from the top and the bottom of the core are also similar to each other, they differ significantly from the ratios at intermediate depths. The results presented here are consistent with the two-component Van Serg core model proposed by Stone and Clayton (1989) and McKay et al. (1988).