Geologic Mapping of Mtm Quadrangles 35337, 40337 and 45337: Deuteronilus

Introduction. Deuteronilus Mensae is a ~1000 km wide area along the highland/lowland dichotomy boundary in the northern mid-latitudes of Mars. In this region, features diagnostic of Martian 'fretted' terrain are observed, including lobate debris aprons, lineated valley fill, and concentric crater fill [1-5]. South of Deuteronilus Mensae are the rugged cratered highlands of Arabia Terra and north of Deuteronilus Mensae the terrain transitions from polygonal mesas to the northern lowlands. To assess the geologic evolution of Martian highland terrains and the modification of these terrains by volatile-driven degradation, we are currently mapping three Mars Transverse Mercator (MTM) quadrangles (MTM 35337, 40337 and 45337) in the Deuteronilus Mensae region (20-25ºE, 32.5-47.5ºN) that extend across the dichotomy boundary. Of particular interest are the geomorphic characteristics of debris aprons and their sources [6-10], the identification of plains that may have been formed by coalescence of apron features , and the stratigraphic relationships between features involved in highland degradation. The mapped geology will provide information on the styles and timing of processes involved in the evolution of Martian highlands and constraints on volatile inventories, environmental conditions, and possible climatic changes in the Deuteronilus Mensae region. Background. The geology of the Deuteronilus Mensae region was first mapped at 1:5M scale using Mariner 9 data [11], and then mapped as part of the Geologic Map of the Eastern Equatorial Region of Mars at 1:15M scale using Viking Orbiter data [12]. Subsequent geologic mapping at 1:1M scale using Viking Orbiter data was done on a smaller portion of the Deuteronilus Mensae region that traverses north-south across the dichotomy boundary (MTM quads 30332, 35332, 40332 and 45332) [13]. Recent studies of the Martian northern plains at 1:15M scale have defined four geologic units covering the Deuteronilus Mensae region [14]. From these studies, the oldest materials in the region are the Noachian highland terrains of Arabia Terra. The lowland plains, fretted valleys, and isolated volcanic units in the Deuteronilus Mensae region are Amazonian to mid-Hesperian in age, whereas most of the youngest materials, such as debris aprons and lightly-to-heavily grooved materials are Amazonian in age. Studies of areas within or adjacent to Arabia Terra have focused on highland denudation by fluvial processes , sedimentary deposition and erosion of highland