Kuiper Quadrangle - Geologic History

Geologic History

The interpretable geologic history of the Kuiper quadrangle is primarily a record of decreasing meteoroid flux during which large craters and basins formed and plains materials were deposited. A decreasing rate of crater production is indicated by progressively fewer craters in each successively younger crater class. Approximately half of the mapped area contains a high density of craters and multiringed basins formed by the intense early bombardment. It is doubtful that any primary crustal material has been preserved without brecciation and redistribution by repeated impacts. The present crater population represents only the craters surviving at the end of the stage of highest meteoroid flux. As the impact flux decreased, cratered plains materials of possible volcanic origin were deposited in broad, low-lying areas, flooding, embaying, or partially burying preexisting craters. The youngest multiringed basins (Renoir, Rodin, and the unnamed basin at 15° S., 15°) formed near the end of this stage (about c3 time), as did the Caloris Basin on the opposite side of the planet (McCauley and others, 1981; Schaber andMcCauley, 1980). Craters that formed still later during the period of low impact rates are well preserved. During this late stage, smooth plains materials were deposited in basins, craters, and localized low areas and have low crater density. The youngest craters are sharp rimmed with bright rays.

The small size of Mercury, its lack of atmosphere, and the cratered nature of its surface invite comparison with the Moon. The geologic histories of the two bodies are similar. Both surfaces record a decreasing impact flux. The cratering history of Mercury was concurrent with episodes of lava flooding (cratered plains) that may have obliterated some basins and flooded large areas in a manner similar to the mare filling on the Moon. Bright-rayed craters, such as Kuiper, mark the youngest events similar to Copernican craters on the Moon; some dark patches along the west margin of the quadrangle may represent late volcanism.

Some differences between the Moon and that part of Mercury observed in this quadrangle may be more apparent than real. Apparent differences may be the result of resolution of the imaging system, and small viewing and illumination angles that do not allow inspection of the surface under varied conditions. Real differences may be the result of Mercury’s size, gravitational field, proximity to the Sun, internal composition and structure, or timing of major volcanic episodes relative to the decrease in impact craters. Surface differences include the preservation of secondary craters around older craters and basins, and the absence of recognizable textured and lineated ejecta blankets such as those surrounding the Imbrium and Orientale Basins on the Moon. Possible differences in volcanic features include the absence of widespread dark mare-type deposits, volcanic domes and cones, and sinuous rilles. Whereas plains and terra divisions may be distinguished on Mercury, the distinct lunar dichotomy of mare and highlands is not present on that half of Mercury observed by Mariner 10.