HR: 0800h
AN: P41A-0187    [Abstracts]
TI: Flank Terraces of Martian Shield Volcanoes: Architecture and Formation
AU: * Byrne, P K
EM: byrnepk@tcd.ie
AF: Department of Geology, Trinity College Dublin, Dublin, 2, Ireland
AU: van Wyk de Vries, B
AF: LMV, Université Blaise Pascal, Clermont Ferrand, 63038, France
AU: Murray, J B
AF: Department of Earth Sciences, The Open University, Milton Keynes, MK7 6BJ, United Kingdom
AU: Troll, V R
AF: Department of Geology, Trinity College Dublin, Dublin, 2, Ireland
AB: Flank terraces are topographically subtle bulge-like structures on the sides of numerous Martian shield volcanoes. They have a gentle convex profile in cross section. These structures have an arcuate outline in plan, and are arranged in a distinctive, imbricate "fish scale" pattern about each terraced edifice. Terraces are generally regarded as compressive features, formed by magma chamber inflation or lithospheric flexure. Some workers argue they are extensional in nature however, due to flank relaxation or gravitational slumping. Previously recognised on Olympus Mons and the Tharsis Montes (Ascraeus, Pavonis, and Arsia), we show that this pattern also exists on Elysium Mons, Hecates Tholus, Albor Tholus, and Ceraunius Tholus, and Alba Patera. Terrace distribution differs between volcanoes, but the characteristic pattern remains the same. Terraces must be late-stage/reactivated structures relative to volcano growth, as they remain visible today. The mechanism responsible for terrace formation probably acts throughout the edifices, as terraces occur at all volcano elevations. Differences in distribution may be due to variations in edifice internal structure, geometry, or the interplay between local and regional stresses. That terraces occur across such a range of Martian volcanoes implies they are size-, slope-, and volcano age-independent structures. The presence and number of other tectonic structures, e.g. calderas and gräben, also vary between terraced volcanoes. Like these other structures, flank terraces may be a fundamental feature of Martian volcano development. In light of these observations, existing formation mechanism hypotheses must be revisited. Magma chamber tumescence, which may have occurred to varying extents on these volcanoes, does not produce convex terrace structures. Both flank relaxation and shallow slumps are associated with volcano spreading, yet none of the Martian examples shows evidence of radially oriented gräben or collapse scars. A feature common to all terraced volcanoes, however, is their large mass. Flexure of the underlying viscoelastic lithosphere in response to these loads may thus lead to internal edifice compression sufficient to form radially directed, circumferentially oriented thrusts.
DE: 5475 Tectonics (8149)
DE: 5480 Volcanism (6063, 8148, 8450)
DE: 8148 Planetary volcanism (5480, 8450)
DE: 8450 Planetary volcanism (5480, 6063, 8148)
DE: 8485 Remote sensing of volcanoes
SC: Planetary Sciences [P]
MN: 2007 Fall Meeting