A possibly fractured crust underneath Cerberus Fossae as inferred from the geometry of giant dikes

Abstract:

The Cerberus Fossae region has been the focus of recent attention due to the discoveries by InSight, mainly, the detection of deep marsquakes underneath the Cerberus graben system. Additionally, the Cerberus fissures have long been candidates for hosting dikes at depth, as suggested by lava and water flows associated with the troughs. We have used: 1) cross section area balancing, a classic structural geology technique, and 2) fundamental Linear Elastic Fracture Mechanics (LEFM), to further support the idea that giant dikes were emplaced in a fractured crust underneath Cerberus Fossae, and that the graben system is dike-induced. Using area balance in 12 topographic profiles we estimated the parameters used in our calculations: dike depths, widths, among others. Dikes have widths between 100-800 m and are located at depths between 400-1500 m. Dike lengths are assumed to be equal to graben lengths. The stress intensity factor (K_I) is a measure of the stress required to open a given fracture length (in this case, dike length). This was calculated for the Cerberus dikes using their geometrical parameters, and assuming the host rock mechanical properties, principally, Young’s Modulus (E) and Poissons ratio (ν). We propose that the crust which hosts the Cerberus dikes is fractured, and thus we used the properties of a ‘rock mass’, i.e., low values of E and ν. The resulting K_I values are between 4-15 GPa m^-0.5. Several arguments support the proposal of a fractured crust. The aspect ratios (width/length) of the inferred dikes are consistent with sublinear scaling, which is characteristic of fluid-induced fractures. Not only this, but the ratios obtained are better aligned with terrestrial dikes emplaced in weak, rather than intact, host rocks. Also, the obtained K_I values are consistent with those found for the nearby Elysium Fossae system, which also likely hosts dikes at depth. Finally, CTX and HiRISE images of the Noachian terrains in which Cerberus Fossae is located show visual evidence of fracture terrains, both near and away from the faults. In conclusion, we propose that the Cerberus Fossae graben host giant dikes at depth and that these were emplaced in a fractured host rock. In preparation for the detection of shallow marsquakes, this must be kept in mind when assessing the seismogenic potential of the Cerberus Fossae region.