Graben system, Rift zone · Fracture belt, Groove belt

Graben system, Rift zone

Extensional troughs similar to rift valleys on Earth. In the equatorial region they run for tens of thousands of kilometres, in belts that join and split apart.

Rift valleys formed by extension – deep canyons – form tight bundles, also called rift zones (Ivanov and Head 2011). Such valleys also make up densely lineated plains and fracture belts, only at a different spacing. The number of down-dropped troughs between faults (grabens) on Venus may run into millions (Studd et al. 2011). As a stratigraphic unit, it is called the Devana Formation, after Devana Chasma (see the plate).

Rift valleys are about 220 km wide, and the amount of extension may be about 2–10 km. In the Atla and Beta–Phoebe systems, built of wide belts of fractures and troughs, the centre stands higher. Along the middle of the rift there runs a valley 2–3 km deep.

Fracture belt, Groove belt

The troughs of fracture belts (see the figure) occur in swarms. They lie closer together and are narrower than the troughs of rift zones. Yet they are still farther apart and easier to tell apart than in the patches of densely lineated plains.

• 272°E
• 35°N