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

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 TiO₂ concentrations were derived from these topographic-photometrically 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% TiO₂ (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 TiO₂ 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 TiO₂ 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.