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

Mineralogy and distribution of rock types in the Tsiolkovsky region of the lunar far-side are evaluated in terms of crustal stratigraphy and evolution . Calibrated multispectral images from five orbits of Clementine data provi de compositional information at a scale that allows diverse geologic featur es to be analyzed and compared. The entire region is seen to be highly anor thositic, with outcrops of relatively pure anorthosite quite common. The cr ater itself has excavated blocks of anorthosite and noritic anorthosite fro m the near-surface highland crust, often in a mixed jumble. The central pea ks of Tsiolkovsky, which have exhumed much deeper material, however, are co mposed 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 zo ne 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 similar to 25 km in this region prior to the Tsiolkovsky impact appears to be (top to bottom) a few kilometers of anorthositic breccias comprising th e megaregolith, a zone of crystalline anorthosite with pockets of noritic a northosite, a zone of anorthosite devoid of iron-bearing minerals, and a zo ne of relatively pure anorthosite containing olivine-rich material, possibl y emplaced as intrusions.