Cone fields in SW Elysium Planitia: Hydrothermal venting on Mars

摘要

We have studied a large cone field in SW Elysium Planitia that shows unique characteristics that have, as yet, not been described elsewhere on Mars. Pitted cones and cone fields are quite common on Mars and the Elysium Planitia region where they have been mainly interpreted as pseudocraters. The cones in the study area differ from cones elsewhere on Mars in morphology, geologic setting, and their assemblage with pitted ridges as well as their close association to Aeolis Planum–Medusae Fossae Formation (MFF) material. The cones appear almost exclusively along an extensive contact zone, several hundred kilometers long, where lava flows that emanated from the Cerberus Fossae flooded fine-grained MFF material of the Aeolis Planum complex. Particularly striking is the observation that several cones in the study area have developed on top of mesas and terraces of Aeolis Planum material that were embayed but not overflowed by lava and can thus not be explained as pseudocraters. We propose that the striking assemblage of these structures was formed by a combination of pseudocrater formation and hydrothermal venting through mesas of Aeolis Planum-MFF material by a process similar to hydrothermal vent complexes on Earth. The voluminous Cerberus Fossae lava flows that flooded the study area covered large parts of Aeolis Planum material, initiating the mobilization of volatiles and leading to hydrothermal activity along the lava-MFF contact. Furthermore, our observations strongly support the hypothesis that the volatile content of the MFF is (or was) high, at least in that part of the MFF constituting the Aeolis Planum complex.