REACTIVATION AND LITHOSPHERE PROPERTIES MAY EXPLAIN DIFFERENCES IN TECTONICS ACROSS THE DICHOTOMY BOUNDARY

Numerical modeling and structural analyses of the Ouachita Mountains, USA have suggested that reactivation of a relict mantle-lithosphere (ML) subduction scar during intra-continental orogenesis was the dominant control over crustal deformation and subsequent geometries of structural landforms. As deformation on one-plate planets such as Mars can be considered intracontinental, we hypothesize that structural geometries on Mars may also reflect the reactivation of scars generated via deep impact cratering events. To investigate our hypothesis, we present 2-D experiments that model deformation associated with the shortening of the Martian crust and ML whilst in the presence of impact-related scarring. We developed a reference model of the Martian lithosphere in Elysium Planitia, the region where the InSight mission collected information about Mars’ interior and where potential models could be constrained or evaluated with geophysical observations. The reference model included a zone of random plastic strain in the crust and ML to simulate a weak, interconnected fracture network generated by impact cratering. The reference model is constrained by thermo- and rheological parameters from past literature and InSight seismic data. We modeled 3 million years of lithospheric shortening, resulting in a crosshatched pattern of faulting that is interpreted as a mix of master faults with high strain rates and low viscosities, and secondary back thrusts with opposing tectonic vergence. Model fault geometries including fault spacing, dip, and alternating vergence concur with past planetary numerical modeling studies of fault geometries using programs like Coulomb and MOVE. We also evaluated many lithospheric parameters to understand their influence on deformation. We find that crustal thickness and the crustal temperature profile are the most dominant parameters over features such as fault depth and the brittle-ductile transition depth (BDT). We developed two additional models depicting the Southern Highlands (SH) and Northern Lowlands (NL) to study the differences in tectonics across the dichotomy boundary. Our models show that a thinner crust (NL) results in a deeper BDT and wider fault spacing, while a thicker crust (SH) results in a ductile lower section of the crust, a shallower BDT and narrow fault spacing.