Abstract

Lunar mare ridges and arches in Mare Serenitatis were mapped to understand better their mode of formation. Mapping of these features indicates that several pre-mare impacts in the Serenitatis area may be responsible for the localization of the circular ridge systems and that the subsurface, pre-mare topography is more complex than previously recognized.

Apollo Lunar Sounder cross sections of ridge systems in southern Serenitatis indicate 50 to 100 m of local relief on these features. Ridges in the southwestern part of the basin mark the boundary of a bench 200 m above the local mare level. As reflected in their orientation, arches and ridges are possibly controlled both by rings of pre-mare basins resulting from impacts and by a more widespread global stress system. Small-scale features of ridges, such as medial lineations and lobate margins, do not conclusively define the origin of the ridges. However, estimates of crustal shortening from Lunar Sounder data and the coincidence of the major ridge system with the Serenitatis mascon suggest that ridges and arches were formed by gravitational readjustments of the mare fill along four probable impact structures and along a north-trending fracture pattern.

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