Interior trough deposits on Mars: Subice volcanoes?

Widespread, several-kilometer-thick successions of layered deposits occur a s mounds that partly fill the troughs or chasmata that compose the Valles M arineris on Mars. Like terrestrial subice volcanoes, the layered deposits o ccur in a volcano-tectonic setting within basins that may have held ponded water or ice. On the basis of their dimensions, morphologies, and associate d catastrophic floods and other geologic events as shown in Viking and new Mars Global Surveyor (MGS) data sets, we suggest that the interior deposits are volcanic in origin and possibly generated by subice eruptions. A tuya origin for the mounds can explain the lack of external sediment, mound heig hts that can rival the plateau, local flat-topped mesas, morphologically di stinct mounds of different ages, horizontal to steep dips, fine-grained mat erials, indications of rare volcanic vents and lava flows, and spectral com position. The extremely diverse layering of west Candor Chasma and possible volcanic cones in Melas may have formed by related subaerial eruptions. Co nsistent with the suggestion that interior deposits are eroding out of the wall rock, some deposits could have been erupted from sites along the walls .