Venus: Limited extension and volcanism along zones of lithospheric weakness

Abstract

Three global‐scale zones of possible tectonic origin are described as occurring along broad, low rises within the Equatorial Highlands on Venus (lat 50° N. to 50° S., long 60° to 310°). The two longest of these tectonic zones, the Aphrodite‐Beta and Themis‐Atla zones, extend for 21,000 and 14,000 km, respectively. Several lines of evidence indicate that Beta and Atla Regiones, located at the only two intersections of the three major tectonic zones, are dynamically supported volcanic terranes associated with currently active volcanism. Rift valleys south of Aphrodite Terra and between Beta and Phoebe Regiones are characterized by 75‐ to 100‐km widths, raised rims, and extensions of only a few tens of kilometers, about the same magnitudes as in continental rifts on the Earth. Horizontal extension on Venus was probably restricted by an early choking‐off of plate motion by high crustal and upper‐mantle temperatures, and the subsequent loss of water and an asthenosphere.