Brian, Anthony William; (2002) A study of large volcanoes and their geological settings on Venus. Doctoral thesis (Ph.D), UCL (University College London).

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Abstract

Magellan SAR, radiometric and gravity data has been used to investigate several areas of venusian geology. The V39 Taussig Quadrangle has been mapped as part of the NASA/USGS VMAP project. The area contains a diverse cross-section of geological features including volcanic plains, coronae, large volcanoes and rifts, and 54 individual units have been identified. The stratigraphic history of the region shows geological processes overlapping and repeating over time, favouring a non-directional stratigraphic model. This style of 'patch' resurfacing is more consistent with an equilibrium resurfacing model. Gravity studies across the region show a top-loading signature located over Maram Corona and the Parga Chasma rift. This suggests that delamination by an active mantle plume may be acting beneath the rift. Studies of Laufey Regio (2°S-16°N, 305-325°E) show that it is a newly discovered topographic rise on Venus. It is dominated by Var and Atanua Montes and surrounded by a concentric ring of wrinkle ridges interpreted to have formed after the onset of centralised volcanism. Detailed geologic mapping has recorded the local stratigraphic history and revealed that many volcanoes and coronae in the area have protracted histories. This also suggests a non-directional stratigraphy. Gravity studies were used to investigate the subsurface structure below Laufey. They indicate the presence of a mantle plume at depth (~190 km) together with a thick crust (~25-30 km) and a large elastic thickness (~55-60 km). The results suggest that Laufey is in a late stage of evolution. A new global survey has identified 134 large venusian volcanoes. The database describes the summit, flank and tectonic characteristics of each feature and together with detailed case studies of individual volcanoes is used to test models of volcano distribution, formation and evolution. There are 0.30 volcanic centres per 106km2 globally, but they do not show a uniform distribution. Volcanoes are clustered around the BAT region and at intermediate to upland altitudes (6051-6052 km). Altitude was not found to influence volcano height, caldera or flow size. The presence of calderas and flank eruptive sites at many volcanoes gives evidence of high level magma storage and drainage. This suggests that whilst neutral buoyancy is an important factor in volcano development many other factors must contribute to edifice growth on Venus.

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