MELTBACK OF HESPERIAN-AGED ICE-RICH DEPOSITS AT THE SOUTH POLE OF MARS: EVIDENCE FOR PROGLACIAL DRAINAGE CHANNELS AND LAKES

MOLA local and regional topographic data support the presence of an extensive Hesperian-aged volatile-rich south polar deposit, the Dorsa Argentea Formation (DAF) and related deposits, underlying the present Amazonian cap. Previous studies of the western margin of the DAF found evidence for channels, cavi, and eskers, indicating meltback and drainage of a portion of an older, more widespread volatile-rich deposit. These channels are broadly distributed, indicating that basal melting was areally widespread and volumetrically significant. The eastern margin of these deposits and the Prometheus Basin hold further evidence for meltback, ponding, and drainage of the volatile-rich deposit. Subdued topography indicates where the surface was once mantled by the DAF. Channels leading from the margins of the subdued topographic region enter nearby craters, indicating drainage of material such as water, ice, and sediment from the DAF. Channels connecting these craters provide evidence for extensive crater flooding, ponding, overtopping, and further drainage of material through a series of craters and into the Prometheus Basin near the edge of the current cap. These channels range from ~600 m to 10 km wide and reach depths on the order of 100s of m. Topography data show that water filled some craters to depths of at least 200 m and possibly as much as 600 m. Materials derived from this lobe of the DAF drained over a distance of ~ 600 km and partially emptied into the Prometheus Basin. These observations combined with the previous work mentioned above indicate that meltback of the older, volatile-rich deposit was a widespread event. Such meltback may have been triggered by changes in local geothermal gradient or climatic conditions.