Basement fabric in the Valles Marineris « rift » on Mars: discovery, significance, and influence on rift development

Access to ancient deep deformation systems on Mars is fundamental to constrain planet dynamics. However, such systems were thought to be unexposed and inaccessible to analysis. Major crustal discontinuities include the planetary dichotomy boundary and the Valles Marineris fault system. Here, we report on two large brittle-ductile shear zones exposed in the deepest parts of Valles Marineris. The shear zones follow the trace of the edge of the Borealis impact basin, thought to represent the planetary dichotomy boundary. Structural analysis and correlation with magnetic anomaly patterns suggest that the shears initiated in the pre-Noachian as part of a normal fault system circumferential about the Borealis impact basin, along which hydrothermal circulation took place. They were then reactivated as right-lateral shears, cumulating tens to hundreds of kilometers of displacement, and again partly reactivated as normal faults during the evolution of Valles Marineris in the Hesperian.

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