Tectonics on Venus

Venus, although very similar to Earth in many ways, has undergone a very different geologic evolution. The geologic and thermal evolution of Venus has long remained a mystery. The Magellan mission revealed a surface covered in lava flows and approximately 1000 pristine impact craters ranging in size from 30–300 km in diameter. This cratering record indicates Venus has a relatively young surface of approximately 500 Ma. However, there is an ongoing debate regarding the thickness of Venus’ lithosphere and, relatedly, how frequently the surface was flooded from volcanic activity. The four largest impact basins on Venus are classified as multiring basins and, due to their large size, offer an opportunity to investigate thermal conditions in Venus’ past

To date, our work has focussed on the formation of the Mead basin to constrain the thermal state of Venus’ lithosphere when the basin formed. Mead has a diameter of 270 km and two circumferential ring faults at approximately 194 and 270 km. The crater floor is currently 700 m below the surrounding terrain and the crater rim is currently 400 m above the surrounding terrain, but these elevations have likely been modified by subsequent viscous relaxation of the basin. The fault locations, however, will not shift as the basin relaxes and their initial locations will depend on the material strengths of both the crust and upper mantle. By testing how different lithospheric thermal gradients affect the formation of Mead Basin and its rings, we can constrain planetary heat flow, and draw conclusions regarding whether Venus had a stagnant lid or active lid in its past.

The geologic history of Venus, although at first glance appears similar to that of Earth, continues to confound researchers. Some of the most fundamental properties of a planet are the method and rate of resurfacing, yet the lack of an identifiable resurfacing mechanism complicates the debate between stagnant and active lid tectonics. Analyzing impact basin morphologies and how they vary with different thermal conditions is one method to overcome this limitation.

This modeling of Mead Basin is the first numerical modeling study to recreate a multiring basin on a planetary body other than the Moon and provides an independent method of testing various geologic histories of Venus. Models of crater and basin development have traditionally focused on recreating lunar basins, but this expansion of the technique onto additional terrestrial bodies will be a useful approach as we continue to strive to understand Venus and beyond.

Collaborators:  This work is led by Brown DEEPS graduate student Evan Bjonnes in collaboration with Brandon. C. Johnson and Alexander J. Evans.

Publications: Bjonnes et al., 2021, Nature Astronomy.