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The eastern margin of the Thaumasia Plateau (EMTP) is characterized by a diversity of tectonic features, which recorded its complex, and still controversial, tectonic history. A detailed structural survey and analyses have been carried out in order to assess the kinematics and relative age of the main deformational events. Combining results from statistics of lineament orientations and density of fault length for each geologic unit and taking into account crosscutting relationships among tectonic structures, three main deformational events have been recognized. The early stage of the tectonic evolution of EMTP is recorded by Noachian units at the southern edge of Melas Dorsa and is represented by N‐S oriented grabens sutured by Early Hesperian formations. Starting from Late Noachian, the extensional stress field became NE‐SW oriented and resulted in the formation of NW‐SE striking sets of grabens. At the boundary between Noachian and Hesperian, the most important change in tectonic regime occurred. The Hesperian tectonics are characterized by an E‐W shortening possibly related to an eastward motion of the Thaumasia Plateau. This tectonic phase likely produced a N‐S‐oriented wrinkle ridges as well as regional folds and thrust faults. E‐W‐oriented preexisting tectonic lineaments could have been reactivated forming regional transfer zones. In this scenario, Coprates Rise, Melas Dorsa, and Thaumasia Ridge could be interpreted as mountain belts resulting from buckling and thrust faulting of the eastern and southern margins of the Thaumasia plateau. The proto‐Valles Marineris could have experienced a left‐lateral component of displacement and played a role of a transfer shear zone.

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[1] We investigated the Ceraunius Fossae area, Northern Tharsis, in order to obtain quantitative information on the tectonic extension affecting this area. Tectonic structures of the Ceraunius Fossae area have been previously described using Viking images and interpreted as extensional structures. Laser altimetry data (MOLA) can be used to quantitatively investigate these structures with a better resolution. We developed a method to obtain E-W oriented profiles (perpendicular to the main tectonic structures) with a sufficiently high resolution to analyze tectonic structures in spite of the low data density in this direction. We interpreted all the recognizable extensional structures along the profiles, and using a simplified structural model, we estimated tectonic extension along these transects. The extension calculated over the entire profiles is 36 km (e 24 = (l 1 À l 0 )/l 0 = (910 km À 874 km)/874 km = 0.041) and 42 km (e 26 = (730 km À 688 km)/688 km = 0.061) along profile 24 and profile 26, respectively. In the most deformed area, extension reaches the value of 22 km (e max = (l 1 À l 0 )/l 0 = (186 km À 164 km)/164 km = 0.134). Since the extension accounted by the topographic doming is negligible, a significant horizontal crustal motion is required to explain the observed extension.