STYLES AND AGES OF VOLCANISM IN SOUTHERN THARSIS, MARS: GEOLOGIC MAPPING OF MTM -35137 QUADRANGLE

At the southernmost extent of the Tharsis volcanic province, a series of volcanic flows and plains is observed to embay and fill low-lying regions of the Martian cratered highlands. This investigation combines traditional geologic mapping of the 1:500K-scale MTM -35137 quadrangle [32.5°-37.5°S, 135°-140°W] with detailed flow field mapping at 1:50K-scale, utilizing high-resolution datasets for Mars to document both geologic history and the nature of volcanic processes.

Geologic mapping of MTM -35137 quadrangle has been completed, including definition of the major geologic units, identification of geologic structures, and evaluation of geologic history from stratigraphic relationships and crater size-frequency distributions. Flow field mapping is ongoing and includes delineation of flow surface textures and features, as well as identification and characterization of flow margins both within and at the edges of the flow field. Smooth plateaus along flow margins are attributed to inflation of the flow as it stagnates while embaying the cratered highlands. MOLA PEDR profiles indicate sheet flows have thickness of 18-96 m near the flow front, with an average of ~51 m.

Stratigraphic relationships and crater counting results provide constraints on the geologic history of the map area, which includes: a) eroded Noachian cratered terrain (highlands) that stabilized in the Early Hesperian Epoch, b) an early episode of volcanism (volcanic plains) that embayed the highlands in the Early Hesperian (~3-3.5 Gy), and c) recent volcanism emplacing vast sheet flows during the Middle Amazonian Epoch (0.5-1 Gy).