摘要：The formation ages of tectonic structures and their spatial distributions were studied in the northwestern Imbrium
and Sinus Iridum regions using images obtained by Terrain Camera and Multiband Imager on board the SELENE
spacecraft and the images obtained by Narrow Angle Camera on board LRO. The formation ages of mare ridges are
constrained by the depositional ages of mare basalts, which are either deformed or dammed by the ridges. For this
purpose, we defined stratigraphic units and determined their depositional ages by crater counting. The degradation
levels of craters dislocated by tectonic structures were also used to determine the youngest limits of the ages of the
tectonic activities. As a result, it was found that the contractions to form mare ridges lasted long after the deposition
of the majority of the mare basalts. There are mare ridges that were tectonically active even in the Copernican Period.
Those young structures are inconsistent with the mascon tectonics hypothesis, which attributes tectonic deformations to the subsidence of voluminous basaltic fills. The global cooling or the cooling of the Procellarum KREEP Terrane region seems to be responsible for them. In addition, we found a graben that was active after the Eratosthenian
Period. It suggests that the global or regional cooling has a stress level low enough to allow the local extensional
tectonics.
关键词：Moon; SELENE (Kaguya); Mare Imbrium; Geohistory; Copernican tectonics; Contraction; Extension
