Crustal stratigraphy of the Al-Khwarizmi–King/Tsiolkovsky–Stark region of the lunar farside as seen by Clementine

Abstract

We have studied the Al-Khawrizmi–King/Tsiolkovsky–Stark region of the lunar farside using both photogeological and Clementine multispectral data in an attempt to determine the stratigraphy, composition and relative maturity of the lunar highlands in the area. The Clementine data show a varied surface composition between the two sites, highlighted by the FeO content of the highland soils, which contain a relatively high iron abundance at King in comparison to Tsiolkovsky. Conversely, on a vertical scale, the highland crust appears to show a matching trend of increasing feldspar content with depth. The upper crust at both sites, while diverse, is generally composed of noritic anorthosite, and exhibits a continual drop in norite content with depth. The higher maficity of the highland materials in and around King compared to those at Tsiolkovsky suggests that King may have excavated a cryptomare or stalled intrusion. While King shows a varied composition overall, mafic materials are present in outcrops on the peaks, walls and in fresh impacts on the crater floor, and mafics were therefore present at all levels in the crust down to at least 14 km (the maximum depth excavated by the King impact event). Further complexity is seen in the north wall of King where a large intrusion cuts through the terracing, suggesting a significant amount of igneous activity in the region. A surface darkening and dark halo crater with a distinct basaltic signature is also present to the south-west of Tsiolkovsky, suggesting a similar cryptomare or stalled intrusion in that region. Overall however, Tsiolkovsky formed in more anorthositic highland crust than is seen at King. These results highlight the lateral diversity of the upper crust, and show a more uniform vertical trend in composition in this region.