Tectonics of Venus

Earth’s Sister Planet

Similarities:Terrestrial SizeDensityRelative distance to the SunRelatively young surfaces

Can you say Hell?

Average surface temperature 4500 CAtmospheric Pressure 90 times Earth’sNo WaterSulfuric Acid CloudsNo magnetic fieldRetrograde rotationForm of tectonism

Definition

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

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

Landscape of Venus (Herrick)

VenusTesserae

Plains

Rift-volcano-coronae zones

EarthContinents

Oceanic plates

Hot spots

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)

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

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

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

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

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