Tsiolkovsky crater: A window into crustal processes on the lunar farside

Abstract

Mineralogy and distribution of rock types in the Tsiolkovsky region of the lunar farside are evaluated in terms of crustal stratigraphy and evolution. Calibrated multispectral images from five orbits of Clementine data provide compositional information at a scale that allows diverse geologic features to be analyzed and compared. The entire region is seen to be highly anorthositic, with outcrops of relatively pure anorthosite quite common. The crater itself has excavated blocks of anorthosite and noritic anorthosite from the near‐surface highland crust, often in a mixed jumble. The central peaks of Tsiolkovsky, which have exhumed much deeper material, however, are composed of relatively pure anorthosite with olivine‐rich zones concentrated near the ridge crests. Boundaries between the anorthosite and olivine‐rich zones are sharp, but spatial relations suggest the coherent olivine‐rich zone is relatively thin (<1 km). The composition of the mare material filling Tsiolkovsky is shown to be low‐titanium basalt. Smaller exposures of mare basalt occur about one crater radius from the rim. The crustal structure to ∼25 km in this region prior to the Tsiolkovsky impact appears to be (top to bottom) a few kilometers of anorthositic breccias comprising the megaregolith, a zone of crystalline anorthosite with pockets of noritic anorthosite, a zone of anorthosite devoid of iron‐bearing minerals, and a zone of relatively pure anorthosite containing olivine‐rich material, possibly emplaced as intrusions.