Structural aspects of Imbrium sculpture, part G

Apollo 16 metric photographs taken at low to high sun angles provided the first stereographic coverage of the distinctive landforms collectively referred to as Imbrium sculpture. The sculpture consists of a series of nearly linear ridges and troughs extending radially outward for more than 1000 km from the rim of the Imbrium Basin. The origin of the ridges and troughs, whether by deposition and impact scoring by fluidized clouds of ejecta from the Imbrium Basin or by faulting and volcanism during and subsequent to basin formation, is controversial. Evidence indicative of the mode of origin of Imbrium sculpture is summarized as follows. Evidence of volcano-tectonic mode of origin is favored by: (1) wide variation in relative age of parts of the sculpture; (2) furrows without rims; (3) absence of ballistic shielding; (4) asymmetry of sculpture; (5) absence of randomly oriented clusters; and (6) association with other features of structural origin. An origin by ejecta scoring and deposition is favored by the gradational ejecta with a Fra Mauro-type texture. Features that are ambiguous as to mode or origin are furrows made of coalesced crater chains and prominent rims on furrows.