Chasma Australe, Mars: Structural Framework for a Catastrophic Outflow Origin

Abstract

Chasma Australe, 500 km long and up to 80 km wide, is the most remarkable of the martian south pole erosional reentrants carved in the polar layered deposits. We have interpreted Chasma Australe erosional and depositional features as evidence for a flood origin, which we have reconstructed using a modified Manning equation. The main characteristics of the flow are a water velocity between 30 and 50 m s¡1 and discharge values between 7 x 10^8 and 3 x 10^9 m3 s-1, very near to MGS data-based estimations for martian outflow channels (D. E. Smith et al. 1998, Science 279, 1686–1692). We thus postulate that Chasma Australe originated in a catastrophic flood. The tectonic study of an area (roughly 20 million km2 in size) around Mars’ south pole included the measurement and projection in rose diagrams of more than 300 lineaments, of which 85 were wrinkle ridges and the rest straight scarps. The whole set of lineaments can be explained by a stress field with a d1 N10ºE in strike, the wrinkle ridges being reverse faults and the other lineaments direct and strike-slip faults. The straight layout of parts of Chasma Australe almost 200 km long suggests that the chasma was carved following a fracture network. The effectiveness of the erosional process (the canyon is up to 1000 m deep) leads us to suspect that this carving was preceded by a sapping period. Endogenetic and exogenetic processes would thus have contributed to the origin of this landform