Geologic map of the Mare Tyrrhenum Quadrangle of Mars
The Mare T yrrhenum quadrangle is bound by lat 0 ˚ and 30 ˚ S and long 225˚ W. and 270˚ W. Th e central part of the quadrangle is dominated by Tyrrhena Patera, a large shield volcano, and associated low-albedo ridge d plains that probably are basaltic lava flows similar to the lunar maria. The western, northern, and eastern margin s of the quadrangle are located in cratered terrains of higher elevation. The great H ellas B asin is located to the southwest of the map area, and the central part of the quadrangle contains a number of arcuate scarps, faults, and ridges that appear to be concentric to Hellas . The southwestern part of the quadrangle contains patches of old knobby terrain that may be ejecta and structurally deformed blocks associated with the formation of Hellas Basin ( Schaber , 1977). Prominent scarps structurally related to the Isidis Basin, located immediately north west, are prominent features in the adjacent Iapygia quadrangle but do not extend into the mapped area. Patches of knobby material in the northwestern part of the quadrangle may be ejecta and structurally deformed areas associated with the formation of the Isidis Basin (Meyer and Grolier, 1977).