Apollo 17 landing site: Topography, photometric corrections, and heterogeneity of the surrounding highland massifs

Abstract

[1] A high-resolution digital elevation model for the Apollo 17 landing site (20°N, 31°E) and surrounding region is used to correct the photometry of Clementine ultraviolet-visible multispectral data to standard viewing and illumination geometry on a pixel-by-pixel basis. FeO and TiO 2 concentrations were derived from these topographicphotometrically corrected data, and steep-sloped highland massifs are used to assess the magnitude of the effects of the correction. The effects are significant, yielding errors as high as 5 wt% FeO and 4 wt% TiO 2 (absolute) on 30°slopes. The magnitude of the correction varies for Sun-facing versus anti-Sun slopes, with greater changes on anti-Sun slopes. Because most of the Apollo 17 sample stations were on surfaces with low slope values (<5°), the topography has only a small effect on the use of the Apollo 17 site for calibration of FeO and TiO 2 parameters. Topographically corrected data and derived compositional information are used to show accurately the variation in composition of the highland units such as the massifs and the Sculptured Hills on a fine scale. Massif compositions are consistent with mixtures of noritic impact melt and feldspathic granulitic material, plus variable amounts of high-Ti basalt on flanks at low elevations and pyroclastic deposits at high elevations, as surmised from previous studies. An unexpected enrichment in FeO at intermediate elevations in some places where massif surfaces have not been covered by mass wasting of impact-melt rich material signals an older volcanic component not previously recognized. This component may be correlative with an old, high-plains volcanic unit exposed northeast of the landing site and north of the Sculptured Hills. Downslope movement of regolith on steep slopes appears to have resulted in compositional or grain size sorting, leading to an apparent enrichment in FeO and TiO 2 from volcanic glass in valleys and draws. The Sculptured Hills have highly variable compositions, ranging from feldspathic patches to exposures of mafic rocks. A strong but localized mafic anomaly within the Sculptured Hills may be a small, postbasin volcanic feature consisting of very low Ti basalt.

The geology of 433 Eros

“…Mechanical separation of grains by composition is not unknown. On the Moon, lower reflectance material found in valleys and draws between massifs north ofthe Apollo 17 landing site are proposed to represent the preferential downslope movement of a mafic component of the regolith (Lucchitta, 1972;Robinson and Jolliff, 2002). Grain separation on Eros has been proposed to explain the anomalous color (Robinson et al, 2001) and geochemical properties (Evans et al, 2001) of the unusual ponded deposits (which show similar color trends to the highreflectance streaks), and a related mechanism may be at work here.…”

Titanium estimates of the central peaks of lunar craters: Implications for sub-surface lithology of moon

“…Determination of absolute TiO 2 content at high resolution ($200 m) for areas with significant local topographic variation within the central peaks is thus constrained by lack of accurate reflectance measurements and the absence of high resolution topographic data (Lucey et al, 1998;Jolliff, 1999;Robinson and Jolliff, 2002). The extent of topography related errors are also sensitive to latitudinal variations (Lucey et al, 1998) as this leads to change in sun angle.…”

40Ar/39Ar and cosmic ray exposure ages of plagioclase-rich lithic fragments from Apollo 17 regolith, 78461

“…However, it should be noted that the plagioclase-rich fragments analyzed in this work were selectively sampled and therefore should not be expected to yield similar results to previous studies based on bulk compositional data (Rhodes et al 1974;Simon et al 1981;Korotev and Kremser 1992). Due to the known lithologic complexity of the Sculptured Hills (Robinson and Jolliff 2002), and the plagioclase-rich fragments targeted for analysis, it is not surprising that the eleven plagioclase-rich lithic fragments were strongly biased against mare basaltic fragments.…”

“…One of the prominent geological features of the valley is the highland unit found near the north massif, the Sculptured Hills. Apollo 17 astronauts sampled the regolith at the base of the Sculptured Hills during their last surface traverse at station 8 (latitude 20.278°N, longitude 30.848°S; Robinson and Jolliff 2002). They dug a 25-cm-deep trench (Wolfe et al 1981) that revealed the best preserved lunar regolith stratigraphy collected during the Apollo missions (Mitchell et al 1973; Fig.…”