Chasma Australe, Mars: Structural framework for a catastrophic outflow origin

Chasma Australe, 500 km long and up to 80 km wide, is the most remarkable o f the martian south pole erosional reentrants carved in the polar layered d eposits. We have interpreted Chasma Australe erosional and depositional fea tures as evidence for a hood origin, which we have reconstructed using a mo dified Manning equation. The main characteristics of the flow are a water v elocity between 30 and 50 m s(-1) and discharge values between 7 x 10(8) an d 3 x 10(9) m(3) s(-1), very near to MGS data-based estimations for martian outflow channels (D. E. Smith et al. 1998, Science 279, 1686-1692). We thu s postulate that Chasma Australe originated in a catastrophic hood. The tectonic study of an area (roughly 20 million km(2) in size) around Mar s' south pole included the measurement and projection in rose diagrams of m ore than 300 lineaments, of which 85 were wrinkle ridges and the rest strai ght scarps, The whole set of lineaments can be explained by a stress field with a sigma(1) N10 degrees E in strike, the wrinkle ridges being reverse f aults and the other lineaments direct and strike-slip faults. The straight layout of parts of Chasma Australe almost 200 km long suggests that the cha sma was carved following a fracture network. The effectiveness of the erosi onal process (the canyon is up to 1000 m deep) leads us to suspect that thi s caning was preceded by a sapping period. Endogenetic and exo-genetic proc esses would thus have contributed to the origin of this landform. (C) Acade mic Press.