1. Tectonics of Venus

2. Earth’s Sister Planet Similarities:  Terrestrial  Size  Density  Relative distance to the Sun  Relatively young surfaces

3. Can you say Hell?  Average surface temperature 450 0 C  Atmospheric Pressure 90 times Earth’s  No Water  Sulfuric Acid Clouds  No magnetic field  Retrograde rotation  Form of tectonism

4. Definition Tectonics is the study of large scale processes that collectively deform the planet’s Surface

5. We are in Agreement Venusian surface features are younger than 1 GA Lithosphere relatively thick 200 km No evidence for present day plate tectonics Present day hot spot volcanism

6. Landscape of Venus (Herrick) Venus  Tesserae  Plains  Rift-volcano-coronae zones Earth  Continents  Oceanic plates  Hot spots

8. Tectonic Models Diapiarism over time (Hansen 2003) Correlation between climate change, surface temperature, and Tectonism (Solomon, et al 1999) Subduction to flood basalts to hot spot volcanism (Herrick 1992, also Basilevsky and Head 2002)

9. Climate Change Model Large flood basalt volcanic event 700 Ma Greenhouse gases expelled Driving force for surface topography is differential between surface temp and mantle temp

10. Diapirism Model Deformation of surface over time by diapirs. Two types –Thermal (responsible for larger features: crustal rises and plateaus) –Compositional (responsible for smaller features: Coronae) Venusian Uniformitarianism

11. Subduction to Hot Spot Model Prior to 800 Ma active subduction and plate tectonics Subduction ceased but flood lava’s flowed from spreading centers (relatively short lived event) Present day hot spot volcanism

12. Conclusions Using earth tectonic and deformation processes not a good model Loss of water is key, puts the brakes on subduction Low to mid grade metamorphic termperature conditions at the surface! No brittle/ductile transition zone, everything behaves plastically even at surface The Herrick model is the most likely

13. References Basilevsky, Alexander T., Head, James, W., 2002 Hansen, V. L., 2003 Herrick, Robert R., 1994 Solomon, Sean C., Bullock, Mark A., Grinspoon, David H., 1999