Physical modelling of large-scale deformational systems in the South Polar Layered Deposits (Promethei Lingula, Mars): new geological constraints and climatic implications

Abstract

Deformation systems (DSs) locally affect the South Polar Layered Deposits (SPLDs) along the margins of the Promethei Lingula ice sheet (part of the southern Martian ice-dome). One example is the 'S 2 ' deformation system, characterized by a complex pattern of brittle and brittle-ductile structures related to kilometre-scale shear zones that deform the sequence. Moreover, soft-sediment structures affect one layer located at the base of the S 2 . An earlier structural analysis suggested that: (1) two deformation stages (D 1 , in which the shear zones developed, and D 2 , in which the D 1 structures were reactivated by deep-seated gravitational slope deformation) occurred, driven by gravity; and (2) there are variations in the bulk composition of the SPLD (which is inferred to be mainly composed of water ice plus basaltic dust). This work supports these structural results through thermal and mechanical modelling of the S 2 sequence. Our modelling results suggest that several layers within the S 2 system are probably composed of, or are mixed with, CO 2 ice, and that the development of the observed deformation is inconsistent with presentday physical conditions. Soft-sediment structures probably formed under warmer surface temperatures during the past, with those warmer temperatures favouring or even triggering ice flow/basal sliding of the Promethei Lingula.Supplementary material: The complete description of the stratigraphy of the analysed S 2 sequence (in table format) is available at

Large-Scale and Deep-Seated Gravitational Slope Deformations on Mars: A Review

“…The role of weak layers on the development of DSGSDs and the melting/softening of icy levels during warmer periods, hypothesized in the first works, was the subject of a subsequent quantitative study. Guallini et al [69] conducted thermal and mechanical modelling to analyze one of the previous described deformation systems. The results showed that different layers of the South Polar Layered Deposits are probably composed of CO 2 ice, which melted or deformed when surface temperatures were higher than the present.…”

“…Not surprisingly, landslides and mass movements also show particular concentrations in this area [2,3,5-7,10,13]. Further large-scale gravitational processes have been recognized in Acheron Dorsum [70], Noctis Labyrinthus [72], and Planum Australe [67][68][69]. The DSGSDs of Planum Australe are of particular interest, as they involve a succession mainly composed of an alternation of layers of dust and water-ice precipitates and represent the first evidence of large-scale gravity-induced deformation in the polar ice cap of a planet [68].…”

“…The faults and the pre-existing tectonic structures show an evident control both on the trench systems of the deformational processes of Acheron Dorsum [70] and on the main scarp of the phenomenon in Noctis Labyrinthus [72]. From this point of view, characteristic DSGSDs are those of Promethei Lingula that not only reactivated pre-existing fault systems (Figure 8) but were also guided by the presence of weak layers at the base of the stratigraphic sequence [68], as demonstrated by thermal and mechanical modelling [69].…”

“…Regarding the DSGSDs in the external portions of Promethei Lingula, the triggering of the large-scale deformational processes could be connected to the outward movement of the ice cap during the warmer periods [68]. This movement would be favored by the presence of weak layers in the stratigraphic sequence, probably melted or deformed when surface temperatures were higher than today, which control the deformational processes and acted as basal detachment planes [69].…”

Volcanism and tectonism across the inner solar system: an overview

“…This finding has important implications for graben sets on numerous worlds, including our understanding of Tharsis-radial graben, which should predate dyke emplacement, the evolution of Venusian radiating fissure systems and, supposedly, dyke-induced graben on the Moon. In a follow-on study of the Promethei Lingula ice sheet on Mars, Guallini et al (2014) integrate structural analysis with thermal and mechanical models to quantify the deformation of part of the ice sheet's South Polar Layered Deposits. They show that parts of these deposits feature soft-sediment deformation and that internal compositions are dominated by CO 2 ice.…”