RELATIVE AGES OF RECENT GLACIAL AND FLUVIAL PROCESSES INDUCED BY CLIMATIC AND GEOTHERMAL EXCURSIONS IN THE HARMAKHIS VALLIS REGION, MARS

Areas of the eastern Hellas region (lat. -35˚ to –42˚S; lon. 91˚ to 98˚E) display enhanced modification of initial topography formed by the Hellas impact. Long and complex history of degradation and modification involves mass wasting processes, tectonism and fluvial activity. Geological mapping of the region (~ 211,914 km2) has been performed on multiple co-registered datasets: Viking imagery, MOLA altimetry, wide and narrow angle MOC images, THEMIS VIS and IR (nighttime and daytime) images, and HRSC images (H0038, H0528) and stereo-derived topography. We used crater size-frequency distributions compiled from the literature and current mapping to constrain stratigraphic positions of different geologic units. Partially buried channels of ambiguous origin in the surrounding plains of the uppermost Harmakhis Vallis and its source region seems to be the oldest channels in surrounding plateaus that most likely date back from Noachian/Hesperian time. Channels (100s km long), chaos areas and water stream uplands in the plains between Niger and Harmakhis indicate fluvial activity. Harmakhis Vallis intersects these features and it is younger. Heat from Tyrrhena Patera probably mobilized and released liquid water that formed Harmakhis Vallis. Stratigraphically younger kettle-like structures, creep textures and ice-facilitated flows in the region are Amazonian in age. Subsequent and the most recent fluvial activity of the region degraded the morphology of the debris-aprons shed from Centauri Montes. Diverse erosion-related morphologies, owing to glaciation and mass-wasting, suggest changes in climatic and local geothermal conditions leading to intermittent flow of liquid water. Utilization of the HRSC data together with other data sets for (a) identifying geomorphic features with higher accuracy and (b) stratigraphic correlations allow us to draw the above conclusion.