Igneous Or Mud Volcanism On Mars? The Case Study Of Hephaestus Fossae

Hephaestus Fossae are a system of northwest trending troughs west of the Elysium Mons volcanic construct on Mars. Pitted cones present in the fossae region have previously been interpreted as both igneous and mud volcanism products based on morphometry and morphology observations. We take advantage of multiple orbital remote sensing datasets to assess the validity of these hypotheses. Newly examined visible and near-infrared spectroscopy observations from the Compact Reconnaissance Imaging Spectrometer for Mars provide the strongest line of evidence for an igneous origin for fossae cones based on the presence of olivine signatures on cone rims. We report an expanded set of morphometric parameter values for 253 cones. Morphometry data from High Resolution Imaging Science Experiment and Context Camera (CTX) digital terrain models reveal that fossae cones appear most similar to terrestrial and putative Martian rootless cones but also exhibit similarities with mud volcanoes on Earth and Mars. Nine hundred and twenty-six mapped cones in our study region exhibit a clustering pattern, as revealed by newly incorporated geospatial analysis, indicating that a nonrandom process controlled feature distribution and individual cones formed near preexisting cones. Cone-fossae relationship constraints are revealed by CTX images, which show individual fossae cutting across preexisting cones. Fossae region cones lack associated flows that characterize mud volcanoes on Earth and Mars. The study region physiographic setting also does not support a sedimentary depocenter mud volcanism formation scenario. Our analysis of cones in the Hephaestus Fossae region adds to the studied diversity of pitted cones on Mars.