Unraveling the geologic and tectonic history of the Memnonia-Sirenum region of Mars: Implications on the early formation of the Tharsis rise.

The geologic and tectonic history of the Memnonia-Sirenum region of Mars has been reconstructed on the basis of geologic mapping and relative-age dating of rock units and structures using crater counts and superposition relations. Comparisons between the ages of rock unit formation and the orientations of the earliest structures associated with Tharsis demonstrate a strong interplay among tectonic, magmatic, and aqueous activity in the Memnonia-Sirenum region. Early Noachian geologic activity identified within this region includes the formation of large northeast-trending, extensional basins. Stratigraphic and tectonic evidence suggests that these basins formed concurrently with the early formation of Tharsis when the dynamo and associated magnetosphere were still in operation. In addition to the ancient basins, later Tharsis-influenced activity includes prominent tectonic fault systems associated with the formation of Tharsis and Arsia Mons. Detailed mapping of the faults indicates that structures associated with Memnonia and Sirenum Fossae resulted from the formation of Tharsis during the Middle to Late Noachian. Late-stage (Amazonian) activity also identified within this region includes valley networks and collapse depressions that are linked and/or occur among Tharsis-centered faults that cut features throughout this region, including Mangala Valles. • The Memnonia-Sirenum region contains some of the oldest stratigraphic units of the western hemisphere region of Mars. • The northeast trending basins and ranges identified appear to be the result of the initial Tharsis upwelling phase. • Continued upwelling resulted in the formation of the ridges and radial faults associated with the center of the uplift. • Basin development was influenced by changing hydrologic conditions linked to the formation of Tharsis. [ABSTRACT FROM AUTHOR]