TESTING HYPOTHESES OF ORIGIN FOR LUNAR FLOOR-FRACTURED CRATERS: VISCOUS RELAXATION VERSUS MAGMATIC INTRUSION AND PREDICTIONS OF ASSOCIATED GRAVITY ANOMALIES

Floor-fractured craters are a class of lunar craters characterized by their anomalously shallow, fractured floors [Schultz 1976; Jozwiak et. al. 2012]; two formation mechanisms have been proposed: 1) viscous relaxation 2) magmatic intrusion and sill formation. Recent morphologic and morphometric analysis of floor-fractured craters using Lunar Orbiter Laser Altimeter (LOLA) data [Jozwiak et. al. 2012] supports the hypothesis that magmatic intrusion and sill formation is a viable mechanism for creating the range of morphologies observed in floor-fractured craters. To further test this hypothesis, we analyze the mechanics of magmatic intrusion and sill formation beneath crater floors. We then make predictions about the magnitude of gravity anomalies that could be associated with both magmatic intrusions and viscously relaxed craters. These analyses allow us to provide predictions for the Gravity Recovery and Interior Laboratory (GRAIL) mission so that this mission can provide definitive distinctions between the two hypotheses. These predictions will allow for direct investigation of the hypothesis that floor-fractured craters are formed by sub-crater magmatic intrusion and sill formation. If an origin for floor-fractured crater formation via magmatic intrusion and sill formation is confirmed, this would provide new constraints on the thermal evolution of the Moon and indicate the presence of widely distributed intrusive volcanism.

Schultz, P., 1976, Floor-Fractured lunar craters: Moon, vol. 15, pp. 241-273.

Jozwiak, L., Head, J., Zuber, M., Smith, D., and Neumann , G., 2012, Lunar Floor-Fractured Craters: Classification, Distribution, Origin and Implications for Magmatism and Shallow Crustal Structure: Journal of Geophysical Research- Planets, in revision.