Geological Context of ANSGA Apollo 17 Double Drive Tube Core 73001/2

Abstract:

Apollo 17 Station 3 is located in Taurus-Littrow on the younger of two light mantle avalanche units, ~50 m southeast of the rim of the partially buried Lara Crater, and on a lobe of the Lee Lincoln fault scarp. (For location details, see figures in Wolfe, et al., 1983). High Sun LROC images led Schmitt, et al. (2017) to conclude that an older, partially buried avalanche lies southeast of the main light mantle deposit. Rover sample 72141 was obtained on the older unit and appears to confirm this conclusion. The young light mantle avalanche settled in place at about 0.100-0.075 Ga (Schmitt, et al. 2017).

Primary Nature of a Light Mantle Avalanche: The light mantle consists of regolith that previously formed on the northeast side of the South Massif. This avalanche source material largely included both commutated melt-breccia, similar to rake sample 72500, and pre-mare litho-clastic ash similar to that present included in rake sample 76500 from the North Massif (Schmitt, 2016). Based on fluidized deposition, collected rock samples, and visual observations, the following are expected: (1) Fines would be concentrated at the top of the avalanche; (2) Coarse fragments would increase in size with depth; (3) the ratio of basalt to impact breccias in the core may be about 1:7; (4) sulfur content about half that of the North Massif regolith (Schmitt, et al. 2017) indicates that trolite (FeS - specific gravity 4.9 g/cm³) may be concentrated at depth.

The minimum depth of the light mantle in the vicinity of Station 3 is about 2 m. Immediately underlying the young light mantle unit, from younger to older, are (1) regolith developed on the old light mantle unit, (2) the old light mantle unit, (3) regolith developed on Lara ejecta, (4) Lara basaltic ejecta, and (5) dark mantle basalt+pyroclastic regolith.

Station 3 Trench Samples: The author dug a shallow trench in the rim of the 10 m diameter Ballet Crater and sampled the four irregular, visible units (73220, 40, 60, 80). These same contrasting regolith units may be encountered in the drive tube core.

References:

Schmittt, H. H. et al. (2017) Icarus, 298.

Schmitt, H. H. (2016) LEAG Ann. Mtg. Abstract 5008.

Wolfe, E. W. et al. (1983) USGS Prof. Paper 1080.