Explosive volcanism in the Tharsis region: Global evidence in the Martian geologic record

[1] A global equatorial set of layered deposits on Mars has been reexamined with Mars Global Surveyor data. The stratigraphy, morphology, and erosional characteristics of units separated by thousands of kilometers are remarkably similar to each other and consistent with a widespread, episodic, subaerial source of fine-grained material. This study is the first to propose a genetic link between many units that have traditionally been considered on a local or regional level, including the Medusae Fossae Formation, Valles Marineris interior deposits, chaotic terrain, Terra Meridiani, and Arabia materials. Mapping relationships suggest that all of these units are post-Noachian in age and formation may have continued until the recent past. Thinning of deposits with increasing distance from the Tharsis rise suggests that much of these materials may be volcanic ash flows and air fall from explosive eruptions in the Tharsis region, analogous to those produced by terrestrial plinian eruptions. Contemporary Martian winds would preferentially transport ash from an eruption plume near Tharsis east or west along the equator depending on the season. Erosion has removed much of the original volcanic ash, and only isolated layered stacks remain, sometimes in topographic depressions that inhibit erosion. Modeling indicates that widespread dispersion of ash after an eruption is easily attainable in present or past atmospheric conditions, consistent with the hypothesis that the far-reaching deposits may be composed of ash from past explosive eruptions in the vicinity of Tharsis.