Ice-rich (periglacial) vs icy (glacial) depressions in the Argyre region, Mars: a proposed cold-climate dichotomy of landforms
On Mars, so-called “scalloped depressions” are widely observed in Utopia Planitia ( UP ) and Malea Planum ( MP ). Typically, they are rimless, metres- to decametres-deep, incised sharply, tiered inwardly, polygonised and sometimes pitted. The depressions seemingly incise terrain that is icy and poss...
| Published in: | Icarus |
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| Main Authors: | , , , |
| Format: | Article in Journal/Newspaper |
| Language: | unknown |
| Published: |
2017
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| Subjects: | |
| Online Access: | https://oro.open.ac.uk/53849/ https://oro.open.ac.uk/53849/1/53849.pdf https://doi.org/10.1016/j.icarus.2016.09.009 |
| Summary: | On Mars, so-called “scalloped depressions” are widely observed in Utopia Planitia ( UP ) and Malea Planum ( MP ). Typically, they are rimless, metres- to decametres-deep, incised sharply, tiered inwardly, polygonised and sometimes pitted. The depressions seemingly incise terrain that is icy and possibly thermokarstic, i.e. produced by the thermal destabilisation of the icy terrain. Agewise, the depressions are thought to be relatively youthful, originating in the Late Amazonian Epoch. Here, we report the presence of similar depressions in the Argyre region ( AR ) (30–60° S; 290–355° E). More importantly, we separate and differentiate these landforms into two groups: (ice-rich) periglacial depressions (Type-1); and, (icy) glacial depressions (Type-2a-c). This differentiation is presented to the Mars community for the first time. Based on a suite of morphological and geological characteristics synonymous with ice-complexes in the Lena Peninsula (eastern Russia) and the Tuktoyaktuk Coastlands (Northwest Territories, Canada), we propose that the Type-1 depressions are ice-rich periglacial basins that have undergone volatile depletion largely by sublimation and as the result of thermal destabilisation. In keeping with the terms and associated definitions derived of terrestrial periglacial-geomorphology, ice-rich refers to permanently frozen-ground in which ice lenses or segregation ice (collectively referenced as excess ice ) have formed. We suggest that the depressions are the product of a multi-step, cold-climate geochronology: (1) Atmospheric precipitation and surface accumulation of an icy mantle during recent high obliquities. (2) Regional or local triple-point conditions and thaw/evaporation of the mantle, either by exogenic forcing, i.e. obliquity-driven rises of aerial and sub-aerial temperatures, or endogenic forcing, i.e. along Argyre impact-related basement structures. (3) Meltwater migration into the regolith, at least to the full depth of the depressions. (4) Freeze-thaw cycling and the formation of ... |
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