Figure 199

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Delisle and Diophantus are two relatively young craters, 27 km and 19 km in diameter, located north of the area shown in Figure 198, in the western reaches of Mare Imbrium. Both are younger than the mare materials in which they are excavated, and also younger than the narrow sinuous rille between them. The rille is sculptured by lineaments radial to the rim crests of Diophantus or Delisle; the lineaments presumably were produced by ejecta from one or both craters.

Both craters exhibit characteristics of young lunar impact craters that have undergone relatively little degradation. The rim crest is sharp, slump terraces inside the walls are distinct, and the density of younger superposed craters is low: only one very young rayed crater, 3 km in diameter, is superposed on Diophantus ejecta.

Five major morphologic facies of crater ejecta can be distinguished in concentric zones away from the crater rim crests: (1) closest to the rim crest, a zone of pitted terrain, dotted with tiny circular craters and large blocks; (2) a zone of rolling troughs and ridges with a smooth surface, grading outward into the third type; (3) elongate or chevronlike secondary impact craters, the rim crests of which form ridges radial to the rim crest of the primary crater; (4) a reticulate network of discontinuous ejecta, forming ridges radial to the rim crest of the primary crater; and (5) isolated secondary impact craters that dot the surface of preexisting mare materials.

The scarp bounded mountains west and southwest of Delisle are massifs of light toned circumbasin materials that are older than the mare and crater materials around them.    -M.J.G.

Report Source: NASA SP-362, Page 191, Figure 199

This web page was created by Francis Ridge for The Lunascan Project
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