UNRAVELING THE FORMATION MECHANISM OF THE CERBERUS FOSSAE, MARS

The Cerberus fossae are among the youngest (<10 Ma) and largest volcano-tectonic features on Mars. The system of fissures is related to a radial dike system that extends ~2000 km ESE from Elysium Mons volcano. Previous work identified the fossae as sources of water and lava erupted onto the adjacent plains. The fossae may represent grabens above subsurface dikes, eruptive fissures, or zones of surface collapse into underlying dikes in response to failure of fractured process zones above the dikes or heating of a cryosphere. The exact formation mechanism is unresolved. Fracture mapping from 5°-15° N, 155°-175° E, was conducted in ArcGIS at a scale of 1:20,000 using HRSC (~12 m/pixel) and CTX (~6 m/pixel) imagery. Topography was derived using the Mars Orbital Laser Altimeter (MOLA) dataset and CTX-derived digital terrain models (DTMs) to constrain fissure segment depths and any uplift signature along the fossae edges. The system is comprised of ~240 NW-SE to WNW-ESE oriented segments with average lengths of 13 km, average widths of 250 m, and depths of up to 1 km. Many segments exhibit an elliptical distribution in both width and depth, and maximum widths are centered along the fissure system length. The width of any given segment is approximately equal to twice the depth at that location (r² = 0.7875). The consistent correlation between segment width and depth implies a similar formation process along the entire fissure system. We interpret surface uplifts identified along transects across the fossae to be consistent with dikes underlying the system at variable depths. Surface uplifts of ~30 m are present along segments with widths of ~150 m and which also sourced eruptive products. Rift zones with underlying dikes in Iceland commonly have width to depth ratios of ~30-125:1, as opposed to 2:1 at Cerberus Fossae, and typically involve numerous parallel faults above the dike system, unlike Cerberus Fossae. Given the vertical walls of the fossae, a 2:1 ratio is inconsistent with width being related to throw along normal faults. We conclude that an evacuated/collapsed dike or eruptive fissure model is more applicable at the Cerberus Fossae, although some grabens may be present locally above dikes. Dikes undergo the greatest dilation midway along their lengths, explaining greater fissure widths in the central portion of the Cerberus Fossae.