MELAS CHASMA - MORPHOLOGY AND TECTONIC PATTERNS IN CENTRAL VALLES MARINERIS (MARS)

The central Valles Marineris is the widest part of the equatorial trou gh system of Mars, Melas Chasma and parts of Coprates and Candor Chasm ata provide some of the clearest clues on the relationships between er osional landforms, deposits and various volcanic and tectonic features . A detailed geomorphic study of the troughs allows the identification of faults and other structures in most parts of this area, in spite o f local obliteration by erosional and depositional processes. Tectonic control on erosional landforms appears mainly in the northern walls o f Melas Chasma and in the edge of the inner plateau above the trough f loor. Longitudinal major faults are identified only along the northern wall. However the trough may not be a simple half graben: another fau lt line is inferred inside Melas Chasma southern walls along the edge of a wide bench of layered deposits. A deep and relatively narrow grab en linking those of Ius and Coprates Chasmata appears to be downfaulte d inside a wider basin with eroded sides. Transverse or oblique faults control some outlines of these erosional landforms, whereas a few mon oclines or faults restricted to the basin beds reveal compressional st resses or differential vertical movements related to the basin develop ment.