Geodynamics of Venus

NASA's Magellan spacecraft mission discovered that Venus has a geologically young surface with a relatively uniform age of 500±200 Ma (million years).

[5] The radar images from the Magellan missions revealed that the terrestrial style of plate tectonics is not active on Venus and the surface currently appears to be immobile.

The Soviet Venera landings revealed that the surface of Venus is essentially basaltic in composition based on geochemical measurements and morphology of volcanic flows.

The global distribution of impact craters that was discovered by the Magellan mission to Venus has led to numerous theories on Venusian resurfacing.

The other end-member is that resurfacing events that wipe out craters are of small spatial area, randomly distributed and frequently occurring.

[18] Catastrophic resurfacing and widespread volcanism can be caused periodically by an increase in mantle temperature due to a change in surface boundary conditions from mobile to stagnant lid.

Solomatov and Moresi (1996) suggested that a reduction in convective stresses caused the surface lid to change from mobile to stagnant.

[13] These parameterized convection models suggest that a cessation of magmatic resurfacing can occur in several ways: (1) the mantle temperature drops sufficiently such that mantle rising adiabatically does not cross the solidus, (2) the molten layer migrates below the solid/melt density inversion at 250–500 km so that no melt can escape, and (3) sublithospheric, small-scale convection stops and conductive thickening of the lid suppresses melting.

However, it has been suggested that Venus's surface has experienced a continuous but geologically rapid decline in tectonic activity due to the secular cooling of the planet, and no catastrophic resurfacing event is required to explain its heat loss.

[21] In a series of subsequent papers, Basilevsky and colleagues extensively developed a model that Guest and Stofan (1999)[22] termed the "directional history" for Venus evolution.

The highly varying levels of post-impact volcanism and deformation that the craters have experienced are consistent with a steady state model of Venus resurfacing.

Planet Venus Observed with Modern Telescope on April 10, 2020
The image is approximately 185 kilometers (115 miles) wide at the base and shows Dickinson, an impact crater 69 kilometers (43 miles) in diameter. The crater is complex, characterized by a partial central ring and a floor flooded by radar-dark and radar-bright materials. The lack of ejecta to the west may indicate that the impactor that produced the crater was an oblique impact from the west. Extensive radar-bright flows that emanate from the crater's eastern walls may represent large volumes of impact melt, or they may be the result of volcanic material released from the subsurface during the cratering event.
The interpretation of tessera as older continental-style cratons is supported by geological analysis of Ashtar Terra and its surroundings. Compression forces, coupled with the inability of the thin basaltic crust to subduct, resulted in fold mountains around the edges of Ishtar. Further compression led to underthrusting of material that subsequently was able to partially melt and feed volcanism in the central plateau. [ 26 ]