A model for the dynamics of crater‐centered intrusion: Application to lunar floor‐fractured craters

Abstract

Lunar floor-fractured craters are a class of craters modified by post-impact mechanisms. They are defined by distinctive shallow floors that are convex or plate-like, sometimes with a wide floor moat bordering the wall region. Radial, concentric, and polygonal floor fractures suggest an endogenous process of modification. Two mechanisms have been proposed to account for such deformations: viscous relaxation and spreading of a magma intrusion at depth below the crater. To test the second assumption and bring more constraints on the intrusion process, we develop a model for the dynamics of magma spreading below an elastic overlying layer with a crater-like topography. As predicted in earlier more qualitative studies, the increase in lithostatic pressure at the crater wall zone prevents the intrusion from spreading laterally, leading to the thickening of the intrusion. Additionally, our model shows that the final crater floor appearance after the uplift, which can be convex or flat, with or without a circular moat bordering the wall zone, depends on the elastic thickness of the layer overlying the intrusion and on the crater size. Our model provides a simple formula to derive the elastic thickness of the overlying layer hence a minimum estimate for the intrusion depth. Finally, our model suggests that crust redistribution by cratering must have controlled magma ascent below most of these craters.

Magma Ascent and Eruption Triggered by Cratering on the Moon

“…Such floor appearances relate to an important intrusion volume. The floor appearance is convex for a thick elastic overlying layer or a small crater; it is flat with a U-shaped moat for a thin elastic overlying layer or a large crater (Thorey & Michaut, 2014). The floor appearance is convex for a thick elastic overlying layer or a small crater; it is flat with a U-shaped moat for a thin elastic overlying layer or a large crater (Thorey & Michaut, 2014).…”

Insights into mare basalt thicknesses on the Moon from intrusive magmatism

“…By studying the deformation affecting the mare basalt layer overlying the intrusion, we place constraints on the local mare thickness. In particular, the theory of magma flow below an elastic plate predicts that the intrusion shape depends on its radius and on the overlying layer flexural wavelength, that itself mainly depends on its elastic thickness (Michaut, 2011;Michaut et al, 2013;Lister et al, 2013;Thorey and Michaut, 2014;Hewitt et al, 2015). Here, we study the topography of these low-slope lunar domes, located in different maria, using the high-resolution Lunar Orbiter Laser Altimeter data from the Lunar Reconnaissance Orbiter.…”

“…We summarize below the model, which is described in detail in several papers (Michaut, 2011;Michaut et al, 2013;Lister et al, 2013;Thorey and Michaut, 2014). The flow driving pressure P is the sum of the bending pressure due to the elastic deformation of the overlying layer and the pressure due to magma weight:…”

“…By applying flow momentum and mass conservation, the following equation for the evolution of the flow thickness with time and radial coordinate has been obtained (Michaut, 2011;Michaut et al, 2013;Lister et al, 2013;Thorey and Michaut, 2014): …”

Volcanism and tectonism across the inner solar system: an overview

“…Similarly, on the basis of their model, Dombard & Gillis (2001) concluded that, compared with topographical relaxation, laccolith emplacement is the more viable formation process. More recent studies utilizing gravity data acquired by the Gravity Recovery and Interior Laboratory (GRAIL) mission demonstrated the presence and dynamics of magmatic intrusive bodies beneath floorfractured craters (Jozwiak et al 2014;Thorey & Michaut 2014).…”