Using lunar graben morphology to elucidate the origin of basin related graben

Tectonic structures can be used to probe the evolution of the stress state of planetary bodies. Similarly, the morphology of individual tectonic structures can be diagnostic of the source of stressed that induced their formation. On the Moon, some of the youngest landforms include lobate scarps that reveal evidence of near-surface contraction. An earlier period of basin localized deformation produced tectonic structures that are radial and concentric to the nearside mare basins. These older features within and proximal to the mare basins include graben and wrinkle ridges that may have been formed by tectonic stresses related to loading by mare basalts. Alternatively, volcanic dike intrusions have been hypothesized to form basin concentric graben.

Elucidating the distribution and characteristics of nearside graben is a key component of mare-localized tectonics. An established relationship between the topographic profile of graben and source of stress can be used to determine whether the graben formed as a result of dike intrusion or passive faulting. A graben by the emplacement of a subsurface dike will have prominent flank uplifts that decay with distance away from the central trough while graben formed by passive faulting exhibit little or no flank uplifts. We take a systematic approach to exploring graben around mascon basins and non-mascon mare and make observations of the graben topography assessing their flank uplift morphology for both mascon (Mare Humorum and Mare Serenitatis) and non-mascon (Oceanus Procellarum and Mare Frigoris) basins.

Preliminary results show no definitive evidence of dike-related graben associated with either mascon (Humorum and Serenitatis) or non-mascon (Procellarum and Frigoris) basins. The mascon tectonic model proposes that contractional and extensional structures in mascon basins are the result of the accumulation of mare basalts on an impact-thinned and weakened lithosphere that results in load induced subsidence and flexure causing contraction in the interior of the basin and extension near the margins. Our results suggests that graben generated by passive normal faulting in non-mascon tectonic settings are also induced by lithospheric flexure.