Major episodes in the geologic history of western promethei Terra, Mars

Abstract

Geologic evolution of the western portion of Promethei Terra (40–50°S, 90–105°E) consists of two major episodes. The first was the formation of a late Noachian–early Hesperian volcanic province. During this episode a kilometer-thick suite (≈0.3 × 10 6 km 3 ) of lavas accumulated to the south of Reull and Harmakhis Valles within a regional depression that probably was formed earlier in a massive erosion. A topographic barrier of the cratered terrains separates the volcanic western Promethei plateau from Hesperia Planum. Thus, the lavas could not originate from Hesperia Planum. The topographic position of western Promethei Terra excludes a possible lava feeding from Hadriaca Patera. Dikes from Tyrrhena Patera potentially could be the lava source. The massive erosion before formation of the lava plateau in western Promethei Terra is poorly consistent, however, with the hypothesis that the distal dikes served as the source and favors emplacement of sills or a local source for the lavas. The second episode after the lava plateau emplacement was surface modification by glacial, fluvial, and aeolian processes. The time of the episode is poorly known, and it could continue from the late Hesperian and through the entire Amazonian epoch. Mesas, channels, and esker-like ridges suggest that at the earlier stages of this episode (late Hesperian–early Amazonian) a glacier or ice dust deposits covered the western Promethei Terra area studied. The 50–60 × 10 3 km 3 formation could contain 15–18 to 40–50 × 10 3 km 3 of ice. This is comparable with the ice involved into of lobate apron formation (5–13 × 10 3 km 3 ) at the later Amazonian stages of western Promethei Terra. Because of the uncertainties in the ice volume estimates, the total amount of water in the earlier glacier and later aprons was approximately the same.