HR: 1340h
AN: P33A-0231    [Abstracts]
TI: Venus' Atla and Beta Regiones: Coronae, Craters and Chasmata
AU: * Jurdy, D M
EM: donna@earth.northwestern.edu
AF: Northwestern University, Department of Geological Sci., Evanston, IL 60208-2150 United States
AU: Stoddard, P R
EM: prs@geol.niu.edu
AF: Northern Illinois University, Department of Geology and Environmental Geosciences, DeKalb, IL 60115-2854 United States
AB: Venus, Earth's "twin" in size and composition, lacks plate tectonics. However, Venus does show evidence of recent uplift as well as both tectonic and volcanic activity. The planet's most pronounced geoid and topographic highs, Atla and Beta Regiones, lie at crossings in a network of chasmata. Hundreds of enigmatic circular features, called "coronae", adorn Venus' surface, ranging in diameter from 60-2600 km with a median of 250 km. Coronae have been modeled and attributed to diapiric-upwellings; however, ancient impacts have been recently proposed as an alternative explanation. We argue here for the diapir hypothesis for corona formation. Corona distribution over Venus' surface is highly non-uniform, with an excess near chasmata. Indeed, some coronae intertwine with chasmata walls, suggesting contemporaneous formation. The raised areas of both Atla and Beta Regiones are ringed by numerous coronae, but neither has coronae at or near their crests, the highest geoid levels. With an evolutionary classification of coronae, we use inferred corona stage to establish that Atla has been active more recently than Beta. Craters on Venus, unlike coronae, have a nearly random distribution over the planet's surface, with a slight, but statistically significant deficit close to chasmata. Only a minority of craters show modification, but an excess of the tectonically or volcanically disturbed craters occurs near chasmata and the uplifted regiones. Impact craters can independently determine relative age, degree of modification, and reorientation of an area on Venus. Low crater densities exist within coronae and surprisingly, even out to 4 radii, whereas we would expect locally higher densities of craters if coronae were themselves very old, unmodified impact features. Furthermore, modification of craters near and within coronae argues for the existence of long-term tectonic and volcanic activity, as opposed to instantaneous formation by ancient impacts. In addition, topographic comparison of coronae with similar-sized craters reveals that coronae lack the symmetry of impact features.
DE: 5420 Impact phenomena, cratering (6022, 8136)
DE: 5475 Tectonics (8149)
DE: 5480 Volcanism (6063, 8148, 8450)
SC: Planetary Sciences [P]
MN: Fall Meeting 2005