Modification of multi-ring basins - The Imbrium model

It is shown that the gross variations in wall height around Imbrium result largely from intersection of the Imbrium basin with pre-existing basins and faulting: angle of impact and slumping played a lesser modifying role. The gross irregularities in plan of the northern part of Imbrium is hypothesized to result from the collapse of large crustal blocks into the Imbrium and Serenitatis cavities. Lithosphere thickness is believed to play an important role in the mechanisms of formation and modification of large craters and basins. The deduction of slow sub-lithospheric flow of material toward the cavity centers does not lend support to the tsunami model, requires a minor modification of the nested-crater model and provides a mechanism for the production of megaterraces. Spatial and temporal lithosphere variations satisfy constraints requiring the overlap of morphology/diameter characteristics, variable onset diameters between planets, variable ring spacings from planet to planet and provide a mechanism for producing local irregularities in ring structures.