Large-scale deformational systems in the South Polar Layered Deposits (Promethei Lingula, Mars): ‘‘soft-sediment’’ and deep-seated gravitational slope deformations mechanisms

• Published in: Icarus
• Main Authors: GUALLINI, LUCA, BROZZETTI, Francesco, MARINANGELI, Lucia
• Other Authors: Guallini, Luca, Brozzetti, Francesco, Marinangeli, Lucia
• Format: Article in Journal/Newspaper
• Language: English
• Published: 2012
• Subjects: geologia planetaria; Marte; geologia strutturale; Ice cap; Ice Sheet; South pole
• Online Access: http://hdl.handle.net/11564/366725; https://doi.org/10.1016/j.icarus.2012.06.023

The present study is the first attempt at a detailed structural and kinematic analysis of large-scale deformational systems observed in the South Polar Layered Deposits (SPLDs) in the Promethei Lingula (PL) margins (Mars). By systematically collecting attitude data referable to previously unknown deformational structures and defining the cross-cut relationships of the structures, we reconstructed a deformational history consisting of two superimposed, well-defined stages. The first stage is dominated by large-scale strike–slip and transtensional faults arranged into conjugate systems and delimiting shear zones that show a wide range of subsidiary structures, including normal and reverse faults, drag folds, boudins, S–C tectonites and sub-horizontal interstratal shear planes marked by sygmoidal boudins. Other typical structures referable to this event are ductile folds (locally true convolute folds) and lobes (balland-pillow structures) affecting certain marker beds of the succession. We suggest that the structural assemblage might be the expression of a shallow soft-sediment tectonics that possibly occurred during warm periods of the South Pole climate. The second stage seems to affect the weaker and in certain cases pre-deformed stratigraphic levels of the SPLD succession. This stage is mainly characterized by extensional deformations caused by gravity. The consequence of the deformations is the nucleation of Deep-Seated Gravitational Slope Deformations (DSGSDs) marked by typical morphostructures, such as scarps, trenches and bulging basal contractant zones. These phenomena were never observed within an ice cap. According to terrestrial modeling, these slow collapses were caused by (1) the presence of detachment levels (i.e., subhorizontal bedding planes) along which the ice-sheet margins can slide and (2) the development of listric faults within the glacial mass, which merge with sub-horizontal shear planes in the subsurface. The presence of complex deformational systems in the SPLD necessarily implies that a ...