Erica Luzzi , Angelo Pio Rossi, Cristian Carli, Francesca Altieri

Arsinoes and Pyrrhae Chaos are two adjacent chaotic terrains located east of Valles Marineris and west of Arabia Terra, on Mars. In this work we produced a morpho‐stratigraphic map of the area, characterized by a volcanic bedrock disrupted into polygonal mesas and knobs (Chaotic Terrain Unit) and two non‐disrupted units. The latter present a spectral variation, likely associated with hydrated minerals, and they are here interpreted as sedimentary units. The reconstructed geological history of the area starts with the emplacement of the basaltic bedrock, followed by the collapse that caused the formation of the chaotic terrains. Since evidences of volcano‐tectonic activity are widespread across the area (e.g. fissure vents/graben, radial and concentric systems of faults, y‐shaped conjunctions, lava flows, pit chains), and an intricate system of lava conduits is hypothesized for the occurrence of such features, we propose the possibility that the whole collapse was caused primarily by volcano‐tectonic processes. In a late stage, after the end of the volcano‐tectonic activity, a lacustrine/evaporitic depositional environment could have set, with the deposition of the non‐disrupted units. The hydrated minerals found in the periphery of the Chaos could be the result of hydrothermal alteration of the basaltic bedrock.