Controls on the Formation of Lunar Multiring Basins

Abstract

Multiring basins dominate the crustal structure, tectonics, and stratigraphy of the Moon.Understanding how these basins form is crucial for understanding the evolution of ancient planetary crusts. To understand how preimpact thermal structure and crustal thickness affect the formation of multiring basins, we simulate the formation of lunar basins and their rings under a range of target and impactor conditions. We find that ring locations, spacing, and offsets are sensitive to lunar thermal gradient (strength of the lithosphere), temperature of the deep lunar mantle (strength of the asthenosphere), and preimpact crustal thickness. We also explore the effect of impactor size on the formation of basin rings and reproduce the observed transition from peak-ring basins to multiring basins and reproduced many observed aspects of ring spacing and location. Our results are in broad agreement with the ring tectonic theory for the formation of basin rings and also suggest that ring tectonic theory applies to the rim scarp of smaller peak-ring basins.Plain Language Summary The largest impact craters on the Moon are multiring basins that exhibit three or more topographic rings. Great volumes of material were ejected and redistributed during the formation of these 1,000-km-scale basins. Formation of these basins is the predominant process driving change of the lunar crust, the outermost layer of the Moon. Why large basins have multiple topographic rings and what they might tell us about the Moon remain poorly understood. Here we simulate the formation of these basins and their rings during an asteroid impact. We explore how thickness of the lunar crust, size of the impacting body, and interior temperature of the Moon affect the formation of basins and their rings. With well-persevered multiring basins and an abundance of high-quality gravity and topography data, the Moon is an ideal location to explore the formation of multiring basins. A better understanding of the formation of these basins will help us understand how similar basins may have affected the crusts of the Earth, Mars, Mercury, and Venus.Other than the 2,000-km-scale elliptical South Pole-Aitken basin Key Points:• We simulate the formation of multiring basins exploring the effect of impactor size, target thermal structure, and crustal thickness • Our simulations reproduce observed trends in ring spacing including the transition from peak-ring to multiring structures • Our results show that basin ring formation is quite sensitive to target thermal structure in general agreement with ring tectonic theory

Large impact cratering during lunar magma ocean solidification

“…Typical lunar basins have a small number of concentric multi-ring features formed by normal faulting due to inward motion of the material filling the transient crater during the modification stage that applies stress to the lithosphere (Fig. 3 left) 24,33,36 . However, if the lithosphere is thin and/or weak (which is mimicked here by the existence of the low-viscosity melt layer), it experiences plastic failure that forms concentric graben-like structures at the surface, possibly similar to the ring structures observed on Jupiter's icy satellites Ganymede and Callisto (Fig.…”

The Thermal Evolution of Mercury Over the Past ∼4.2 Ga as Revealed by Relaxation States of Mantle Plugs Beneath Impact Basins

“…The elevated mantle uplifts beneath impact basins were formed following the floor rebound induced by impact excavation (Spudis, 2005). The surface topography and subsurface crustal structures of Mercury impact basins are dominated by both the thermal state of the lithosphere when the impact occurred (Freed et al, 2014; Johnson et al, 2018; Potter & Head, 2017) and the subsequent viscous relaxation process (Mohit et al, 2009). The duration of the viscous relaxation process and the final geometric structures are mainly controlled by the temperature at the base of the mantle plug (i.e., at the crust‐mantle boundary; Temp Moho ) as well as the viscosity of the crust (Kamata et al, 2013).…”

A nonlinear and time‐dependent visco‐elasto‐plastic rheology model for studying shock‐physics phenomena

“…Such a cavity is not stable because differential stresses in the surrounding rocks reach 10 9 Pa or more. Melosh and McKinnon 31 speculated that the inward flow of the underlying mantle may be responsible for the mountainous rings surrounding large lunar basins, a speculation that is now supported by the model by Johnson et al 32 of the formation and collapse of the Moon's Orientale basin, a computation that used the algorithm described in this paper.…”

“…where the individual terms, derived from Equation 22, are given by: Figure 6 shows these individual contributions to the stress during the course of our example computation. Note that the magnitude of these contributions depends linearly on the size of the time increment (Δt), as Equations (32) and (33) require. Also note the negative sign in the viscous term of Equation (31) indicates that the viscous contribution lessens the instantaneous elastic stresses.…”

“…In the meantime, the algorithm described in this paper has been incorporated into the developer version of iSALE and is used in the form described here by Johnson et al 32 and Lyons et al 64 A version modified for ice rheology appeared in Johnson et al, 65 Silber et al, 66 and Bowling et al 67 We anticipate that future publications will use this rheology as the developer version of iSALE is migrated to the user version.…”