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Highlights • We test hypotheses for the formation of craters within martian glacial deposits. • Nine crater types and multiple degradation sequences observed. • There is a small size difference between ring-mold craters and bowl-shaped craters. • Flow lineations cross-cut older ring-mold craters but not other crater types. • Observations most consistent with formation by mantle emplacement and dissection. Abstract Lobate debris aprons (LDA), lineated valley fill (LVF), and concentric crater fill (CCF) on Mars, interpreted to be debris-covered glaciers, possess craters with a suite of distinct interior landforms (called "ring-mold craters") that have been attributed to the presence of glacial ice at depth or surface modification processes. We tested current hypotheses for the formation of ring-mold craters by conducting a comprehensive analysis of the size and morphology of 16,457 impact craters ≥125 m in diameter formed within glacial deposits in Deuteronilus Mensae. Two major groups, bowl-shaped craters and ring-mold craters, are found, with at least nine distinct crater types. While there is statistical difference in median diameters between these crater types, this difference is relatively small and is within the estimated uncertainty in diameter measurements and may be related to more enhanced erosion of the rims of ring-mold craters. Clear degradation sequences are observed, supporting a role for post-impact modification in producing at least some of the diversity in crater landforms. The spatial density of ring-mold craters is also directly correlated with the development of LDA, LVF, and CCF surface textures. Flow lineations cross-cut two ring-mold crater types but they maintain their circular planforms in some cases, suggesting that the craters initially formed completely within mantling layers deposited after glacial flow had ceased. We also find analogous craters in non-glacial units; glacial ice is therefore not required to form the observed morphologic diversity. Our observations are most consistent with formation of crater landforms by emplacement and modification of at least two depositional episodes of icy dust (i.e., "mantle"). This mantle was initially tens of meters in thickness to support crater formation, and has experienced much downwasting and erosion since emplacement. Derived crater retention ages of 460 Ma for LDA, LVF, and CCF features in the region therefore reflect deposition of mantle units and only give a very minimum age for the formation of LDA, LVF, and CCF. [ABSTRACT FROM AUTHOR]

Impact basins provide windows into the crustal structure and stratigraphy of planetary bodies; however, interpreting the stratigraphic origin of basin materials requires an understanding of the processes controlling basin formation and morphology. Peak-ring basins (exhibiting a rim crest and single interior ring of peaks) provide important insight into the basin-formation process, as they are transitional between complex craters with central peaks and larger multi-ring basins. New image and altimetry data from the Lunar Reconnaissance Orbiter as well as a suite of remote sensing datasets have permitted a reassessment of the origin of lunar peak-ring basins. We synthesize morphometric, spectroscopic, and gravity observations of lunar peak-ring basins and describe two working hypotheses for the formation of peak rings that involve interactions between inward collapsing walls of the transient cavity and large central uplifts of the crust and mantle. Major facets of our observations are then compared and discussed in the context of numerical simulations of peak-ring basin formation in order to plot a course for future model refinement and development. [ABSTRACT FROM AUTHOR]

Important to understanding the process of basin formation on planetary bodies are constraints on the mineralogy and depths of origin of interior ring structures. We summarize previous analyses of the mineralogy of basin materials on the Moon and use hyperspectral image-cubes from the Chandrayaan-1’s Moon Mineralogy Mapper (M 3 ) to determine the mineralogy of interior rings in lunar protobasins and peak-ring basins. Nearly all peak rings outside of South Pole-Aitken (SPA) basin have extensive outcrops of pure anorthosite (⩾99% plagioclase) on the order of several square kilometers in areal dimensions. No obvious mantle components were identified. Outcrops spectrally dominated by pyroxene occur within SPA and other areas of thinner crust, such as regions within large ancient impact basins. In addition, many outcrops of candidate shocked plagioclase are observed within the same peak rings containing crystalline plagioclase. These spectral observations strongly support a crustal origin for peak rings on the Moon. Recent analyses of the Orientale basin and other lunar basins show that the inner rings of multi-ring basins are also anorthosite-rich and therefore derived from the lunar crust. To further constrain the depths of origin of materials forming peak rings, we compare the pre-impact crustal thickness for each basin with calculated vertical reference points, including: (1) maximum depth of excavation, which is the deepest point at which the crater will excavate material, (2) maximum depth of melting, which is deeper than the maximum depth of excavation and represents the maximum extent of impact-induced melting beneath the sub-impact point, and (3) maximum depth of the transient cavity, which is deepest part of the growing transient cavity that is formed of both excavated and displaced target material. Taken together with the observed mineralogy, the origin of peak-ring lithologies is constrained to stratigraphic levels near the maximum depth of excavation and likely shallower than this if the lower crust is comprised of noritic materials. The maximum depth of melting for peak-ring basins extends far into the mantle and is therefore not a valid proxy for estimating the depth of origin of materials forming peak rings. We find that our estimates of the depths of origin of peak-ring materials are consistent with current models of peak-ring formation, including predictions by hydrocode simulations and conceptual models emphasizing the role of interior impact melting and centro-symmetric collapse of the walls of the transient cavity. Firmer constraints on the depths of origin of peak rings on the Moon await an improved understanding of the crustal compositional structure, particularly that of the lower crust, and improved model predictions on the sampling depths and shock pressures experienced by uplifted peak-ring materials. [ABSTRACT FROM AUTHOR]

Abstract: Impact craters on planetary bodies transition with increasing size from simple, to complex, to peak-ring basins and finally to multi-ring basins. Important to understanding the relationship between complex craters with central peaks and multi-ring basins is the analysis of protobasins (exhibiting a rim crest and interior ring plus a central peak) and peak-ring basins (exhibiting a rim crest and an interior ring). New data have permitted improved portrayal and classification of these transitional features on the Moon. We used new 128pixel/degree gridded topographic data from the Lunar Orbiter Laser Altimeter (LOLA) instrument onboard the Lunar Reconnaissance Orbiter, combined with image mosaics, to conduct a survey of craters>50km in diameter on the Moon and to update the existing catalogs of lunar peak-ring basins and protobasins. Our updated catalog includes 17 peak-ring basins (rim-crest diameters range from 207km to 582km, geometric mean=343km) and 3 protobasins (137–170km, geometric mean=157km). Several basins inferred to be multi-ring basins in prior studies (Apollo, Moscoviense, Grimaldi, Freundlich–Sharonov, Coulomb–Sarton, and Korolev) are now classified as peak-ring basins due to their similarities with lunar peak-ring basin morphologies and absence of definitive topographic ring structures greater than two in number. We also include in our catalog 23 craters exhibiting small ring-like clusters of peaks (50–205km, geometric mean=81km); one (Humboldt) exhibits a rim-crest diameter and an interior morphology that may be uniquely transitional to the process of forming peak rings. A power-law fit to ring diameters (D ring) and rim-crest diameters (D r) of peak-ring basins on the Moon [D ring =0.14±0.10(D r)1.21±0.13] reveals a trend that is very similar to a power-law fit to peak-ring basin diameters on Mercury [D ring =0.25±0.14(D rim)1.13±0.10] [Baker, D.M.H. et al. [2011]. Planet. Space Sci., in press]. Plots of ring/rim-crest ratios versus rim-crest diameters for peak-ring basins and protobasins on the Moon also reveal a continuous, nonlinear trend that is similar to trends observed for Mercury and Venus and suggest that protobasins and peak-ring basins are parts of a continuum of basin morphologies. The surface density of peak-ring basins on the Moon (4.5×10−7 perkm2) is a factor of two less than Mercury (9.9×10−7 perkm2), which may be a function of their widely different mean impact velocities (19.4km/s and 42.5km/s, respectively) and differences in peak-ring basin onset diameters. New calculations of the onset diameter for peak-ring basins on the Moon and the terrestrial planets re-affirm previous analyses that the Moon has the largest onset diameter for peak-ring basins in the inner Solar System. Comparisons of the predictions of models for the formation of peak-ring basins with the characteristics of the new basin catalog for the Moon suggest that formation and modification of an interior melt cavity and nonlinear scaling of impact melt volume with crater diameter provide important controls on the development of peak rings. In particular, a power-law model of growth of an interior melt cavity with increasing crater diameter is consistent with power-law fits to the peak-ring basin data for the Moon and Mercury. We suggest that the relationship between the depth of melting and depth of the transient cavity offers a plausible control on the onset diameter and subsequent development of peak-ring basins and also multi-ring basins, which is consistent with both planetary gravitational acceleration and mean impact velocity being important in determining the onset of basin morphological forms on the terrestrial planets. [Copyright &y& Elsevier]