Structural and Geological Interpretation of Posidonius Crater on the Moon

Abstract:

Posidonius crater locates on northeastern rim parts of the Serenitatis basin and is a typical floor-fractured crater. Because of Posidonius is located lunar central nearside and easily observed by ground-base telescope, the complex texture of crater floor attracted planetary scientist attention from before lunar exportation era. However, origin or formation histories of floor fractures are not fully resolved yet. In this study, we try to estimate geologic histories of Posidonius crater based on topographic data and multiband image data obtained by Terrain Camera (TC) and Multiband Imager (MI) onboard Kaguya.

A part of crater floor of Posidonius is flooded by mare basalt. Previous studies interpreted that the source of mare basalt is located somewhere at Mare Serenitatis and flooded into Posidonius crater, then sinuous rill (Rimae Posidonius) is the resulting structure of flooded basalt flow. However, based on TC topographic data, sinuous rill feature indicate opposite flow direction to previous interpretations. Based on TC topographic data, we could interpret topographic features as follows; Rimare Posidonius flow from volcanic vent located at northern edge of Posidonius crater floor and flow out to Mare Serenitatis at western rim, the central part of crater floor slightly leaned to west and broken in several regions.

From band depth of MI data, eastern part of crater floor is mostly consisted by highland materials and complex rills are basically not showing the basaltic feature.

Combined both analysis results, we interpret the cause of complex structure of Posidonius crater is as follows; after crater formation, large sill intruded below crater floor and uppermost layer of crater floor is delaminated from the basement then floats on basaltic intrusion as “otoshibuta” (Japanese style lid for stew). Complex fracture was probably formed delamination and flotation stage by mechanical stress.