Evaluating transtension on Mars: The case of Ulysses Fossae, Tharsis

This work presents a structural analysis of the southern half of Ulysses Fossae, a transtensional mega-structure located in the Martian Western Hemisphere, at the western slope of the Tharsis rise, Mars. The analysis includes a structural mapping, a determination of the trend of the main fracture systems, an approximate determination of their age, the construction of five topographic profiles, and an estimation of the elongation amount verified along each profile direction. The structures of the studied zone are typically normal faults and grabens affecting Hesperian units (3.6–3.5 Ga according to crater-counting techniques). The structure is N-S-oriented, although later structures show NW-SE azimuths. These results have been checked against the predictions of a simple kinematic model of transtension, which suggest pure-shear dominated flow. The obtained values of kinematic vorticity (0.1–0.65) vary along and across the structures. The presence of a large-scale shear zone at depth is the explanation preferred in this work.