Mechanical conditions and modes of paraglacial deep-seated gravitational spreading in Valles Marineris, Mars

Deep-seated gravitational slope deformation scaling on Mars and Earth: same fate for different initial conditions and structural evolutions

“…In most described terrestrial instances, such as in the Alps of Europe, Japan, New Zealand, and the Andes, DSGSD has been described in mountain ridges glaciated during the Quaternary (see a review in the Supplement of Mège and Bourgeois, 2011). Such a postglacial context, in the Valles Marineris case, is adapted to the recently identified and widespread glacial land system (Gourronc et al, 2014;Mège et al, 2017;Dębniak et al, 2017), which is also in agreement with expected slope deformation in this context (Makowska et al, 2016), and additionally provides a good framework (Mège and Bourgeois, 2011;Cull et al, 2014) to understand the detected mineralogical occurrences as from the compact reconnaissance imaging spectrometer for Mars (CRISM) (Roach et al, 2010;Cull et al, 2014). Postglacial deformation, as far as DSGSD is concerned, includes the paraglacial response of rock slopes to changing stress conditions after glacier retreat (e.g.…”

“…DSGSD develops independently of the structure and lithology of the topographic ridge, although major strength contrasts affect the strain field and therefore the expected observed deformation (e.g. Makowska et al, 2016). Such contrasts may be provided by weak-strong rock contrasts and major faults.…”

“…In some other instances, the bottom of the slope is not deformed and the extension in the upper part of the ridge is absorbed within the ridge, the density of which is locally increased (Discenza et al, 2011), possibly by crushing (Beck, 1968;Mahr, 1977). Makowska et al (2016) found that in homogeneous rock DS-GSD in the upper part of the slope and at the bottom is indeed disconnected and that an internal core of intensely deformed rock underlies the uphill-facing scarps developed in the upper part of the slope. In this work we cannot explicitly take lower ridge deformation into account, if any, due to systematic blanketing of basal ridge bedrock structure by a huge debris slope; nevertheless, the corresponding horizontal deformation that would result is implicitly accounted for by considering the measurement of total ridge width where DSGSD is observed and where it is not.…”

The case against vast glaciation in Valles Marineris, Mars

“…This usually involves mass creep of rock, sometimes along a shear surface, to form crestal grabens and uphill-facing fault scarps along ridge slopes, compensated for by downslope bulging and folding (Bovis and Evans, 1996;Discenza et al, 2011). In Marineris, Mège and Bourgeois (2011) and Makowska et al (2016) present these features as post-glacial, forming with slope debutressing following a retreating ice mass. Indeed on Earth, sackungen features are observed in regions where deglacial unloading and subsequent rebound has occurred in valleys either side (McCalpin and Irvine, 1995;Jarman, 2006), but such features are not exclusively glacial.…”

“…A school of thought regarding the possibility of a Late Noachian to Late Hesperian (~3.7-3.0 Ga) polythermal glaciation within the Valles Marineris of Mars has emerged over the last decade (Rossi et al, 2000;Thaisen et al, 2008;Fueten et al, 2011;Mège and Bourgeois, 2011;Cull et al, 2014;Gourronc et al, 2014;Makowska et al, 2016;Dębniak et al, 2017). The hypothesis has been fuelled by reported observations of: 1) morphology including ice surface trimlines, deep scour, lateral banks, terminal and ground moraines, outwash plains, patterned ground, truncated spurs, hanging valleys, and hummocky terrain (Fueten et al, 2011;Mège and Bourgeois, 2011;Gourronc et al, 2014;Dębniak et al, 2017); 2) mineralogy including jarosite along the trimline (Cull et al, 2014); and 3) structural reorganisation including crestal ridge slumping and gravitational spreading (Makowska et al, 2016;Mège and Bourgeois, 2011).…”