Abstract DGP2026-50

The Martian crustal dichotomy marks a morphological boundary between the heavily cratered southern highlands and the relatively smooth northern lowlands. Dichotomy’s origin has been related to endogenic or exogenic mechanisms occurred at different stages of planet formation. Its geological evolution is characterized by deformation processes such as fracturing and normal faulting.

In the west, the dichotomy is a smooth topographic transition (e.g., Arabia Terra), while in the east (Nilosyrtis) it is characterized by a sharp prominent scarp. The eastern dichotomy is dissected by extensional faults, distributed for 40–100 km in the highlands; the corresponding lowlands, show a set of compressional ridges oriented parallel to the dichotomy, up to 1000 km to the north east.  This is the only section of the dichotomy where extensional faults in the highlands are subparallel to compressional structures in the lowlands. Morphologically, it resembles a terrestrial passive margin affected by gravity-driven deformation occurring above a basal detachment, in which an up-dip extensional domain is connected to a subparallel down-dip compressional domain, through a relatively undeformed transitional domain.

Through high-resolution remote sensing mapping integrated with 2D kinematic and numerical modelling, we investigate the possibility that the northeastern dichotomy in the Nilosyrtis area was reshaped by gravity-driven deformation. We characterize the timing of deformation, the depth and the nature of the common basal detachment and the possibility to have gravitational deformation under Martian gravity.

Kinematic modelling is applied to selected compressional ridges to characterize their detachment depth and shortening. The modelling is carried out using a combined approach based on Area Depth Strain and Trishear modelling integrated with Fault Parallel Flow. Detachment depth of the extensional faults is obtained from the intersection of the two opposite-dipping faults delimiting grabens, assuming a fault dip of 60°.

The kinematic modelling is compared to 2D numerical modelling, used to investigate the role of gravity, viscosity, pore pressure and detachment distribution in comparison with the three structural domains observed in the study area. We present three models: Model 1 comprises a frictional layer resembling an overpressured shale detachment, while Model 2 represents a weak viscous-like layer simulating a mixture of salt, ice and basalt debris. They assume a common and continuous basal detachment in both the highlands and the lowlands. Model 3 comprises  a frictional shallower detachment in the highlands and a weak viscous-like detachment in the lowlands.

Results suggest the presence of a gravity-driven system, deformed on top of a viscous detachment in the lowlands, linked to a more frictional basal detachment in the highlands. The frictional detachment in the highlands would be linked to a sedimentary interlayer of between flood basalts. The weak detachment in the lowlands would be linked to a mixture of salt, ice and basalt debris. This interpretation supports a giant Borealis impact, followed by evaporites precipitations from a hypersaline sea, later reorganized by impacts and buried beneath below volcanic deposits. We propose the existence of the ancient, partially buried and eroded Nilosyrtis gravity-driven fold-thrust belt, which developed between Late Noachian and Early Hesperian.