Erica Luzzi

• For my PhD project I investigated the surface characteristics and tested a possible formation mechanism of two Martian chaotic terrains: Arsinoes and Pyrrhae Chaos. These regions on Mars are characterized by the disruption of the basaltic bedrock into polygonal blocks, later covered by post-collapse sedimentary units. Such investigation included spectral analyses, that revealed the occurrence of basaltic mineralogies in the bedrock and hydrated minerals within and right outside Arsinoes Chaos, structural observations, that showed a prevalence of volcano-tectonic features in the area, and morpho-stratigraphic mapping, that allowed to have a clearer view on the geological history of these two chaotic terrains. Given the paucity of aqueous-related evidence, I developed a hypothesis for the formation mechanism that generated the collapse of chaotic terrain: a piecemeal caldera collapse. This particular type of collapse, known as chaotic caldera collapse, consists of multiple cycles of inflation and deflation of a buried magma chamber, resulting in the disruption of the overlying brittle materials into polygonal blocks, bounded by intersecting radial and concentric faults. This hypothesis was tested in an analog experiment in laboratory, where the process was reproduced, and the results suggest that piecemeal caldera collapse could in fact explain the peculiar characteristics of chaotic terrains, without involving water (either liquid or ice): this would justify the formation of those chaotic terrains where outflow channels and any fluvial feature are not present, and hydrated minerals are exiguous. In the experiment, the comparison was made also with a similar type of terrain, occurring both on Mars and on the Moon (where aquifers do not exist), the Floor-Fractured craters (FFCs). The last part of my project was dedicated to structural analyses on the faults within Lunar FFCs, providing more insights on the complex geological history of these heavily fractured terrains.