GEOLOGIC MAPPING OF VOLATILE-RICH TERRAINS AROUND UPPER DAO AND NIGER VALLES, NORTHEAST HELLAS, MAR

Through geologic mapping and morphologic and spectral analyses, we are investigating the geologic and hydrologic histories of the eastern rim of Hellas, where important spatial and temporal relationships between volcanic and volatile-driven processes are preserved. This region displays a unique confluence of ancient rugged highlands, volcanic terrains, the canyons of Dao and Niger Valles, channelized plains, and geologically young volatile-rich mass wasting and mantling deposits.

We are using ArcGIS to compile image, topographic, and spectral datasets in order to produce a 1:1M-scale geologic map of MTM quadrangles -35262, -35267 and -35272. THEMIS day and night thermal infrared brightness temperature mosaics (~100 m/pixel) are the primary mapping bases and are being used to distinguish between units with different thermophysical properties. CTX (~5 m/pixel) and THEMIS VIS (~18 m/pixel) images provide complementary spatial coverage and serve as context for high-resolution HiRISE (<1 m/pixel) and MOC-NA (~1.5-12 m/pixel) images that allow detailed analyses of mapped units and features. CRISM multispectral (~100-200 m/pixel) and hyperspectral (~18-36 m/pixel) data show the occurrence and distribution of primary minerals and their alteration products within surficial materials. Crater size-frequency distribution statistics and stratigraphic relationships are used to determine relative ages.

We are mapping geologic units and features that define four prominent terrains within the map area, including highlands in the west and southeast, the Tyrrhenus Mons flow field in the east, the southern flank materials of Hadriacus Mons (HM), and plains that occupy the central part of the map area. Mapping shows that volatile-related processes modified nearly every surface in the map area. Evidence for flow of fluids across the surface includes gullies, channels, and valley networks. Evidence for modification by subsurface/interstitial volatiles is preserved as areas of collapsed plains, fluidized ejecta blankets, and lobate mass wasting deposits. The ejecta blankets of most fresh craters display a continuous proximal deposit with lobate edges, and a discontinuous knobby and etched distal deposit.