MARE INFILLING OF TSIOLKOVSKY CRATER, THE MOON

The 180-km diameter Tsiolkovsky crater (20^oS, 129^oE) displays several features unique on the lunar farside, including the best example of farside mare volcanism. Topographic data from Lunar Orbiter Laser Altimeter (LOLA) show that there is >450 m elevation difference between the northern and southern portions of the crater floor. This observation favors multiple eruptions, all of which failed to resurface the entire floor. We infer that the mare-filling eruptions had vents in the NE portion of the floor, and were most likely volume-limited. Lunar Reconnaissance Orbiter Camera (LROC) Narrow Angle Camera (NAC) images reveal graben and ridges around the perimeter of the mare infill, as well as depressions which provide clues to the mare lava emplacement. The fractures may be representative of local subsidence within the mare units, comparable to the deformation of Mare Serenitatis. The depressions may provide information on the rate of mare infilling during each eruption as they suggest that the mare flows were produced by low effusion-rate eruptions with associated flow inflation. Comparable "lava pits" are features of low-effusion rate eruptions in Hawaii. We have found no lava flow fronts to confirm this interpretation, nor do we find evidence for benches or "bath-tub rings" on the southern perimeter of the mare to confirm (or refute) changes in mare level due to subsidence of the floor. However, Kaguya topographic data reveal there are local elevation differences of ~100 m, as well as tilted blocks and up-doming, of the mare floor. Oblique views of the floor reveal indicate that at least the northern floor experienced subsidence comparable to the deformation of certain perched lava ponds on Earth. Morphologic evidence for multiple lava flows within Tsiolkovsky crater raises the possibility that the eruptions took place over an extended period of time. However, crater counts for selected areas of the crater reveal that there is little age difference between different parts of the crater floor. These counts also indicate that the mare lavas were erupted soon after the formation of the crater as well as the crater rim collapse which produced the giant landslide on the NW crater rim.