Coldspots or hotspots? The origin of plateau-shaped highlands on Venus

A compelling question for the terrestrial planets is the origin of the highland regions on Venus. Data on the topography, gravity signature, and surface morphology returned by the Pioneer Venus, Venera 15/16, and Magellan spacecraft represent a basis for dividing these highlands into two distinct groups: volcanic rises and plateau-shaped highlands. Volcanic rises are generally thought to be due to mantle upwellings in the form of large mantle plumes and are thus similar in origin to terrestrial hotspots. There is less agreement as to the origin of plateau-shaped highlands (PSH). Coldspot mantle downwelling can lead to the formation of a highland region under Venus conditions, and previous to Magellan some PSH (particularly W. Ishtar Terra and Ovda and Thetis Regiones) were suggested to be compressionally deformed regions of thickened crust created by mantle downwelling. A hotspot model proposes that such regions are formed by magmatism and tectonism related to the near-surface ascent of either the diapir-shaped large mantle plume or a solitary disturbance propagating up a plume conduit. The characteristics of both volcanic rises and plateau-shaped highlands on Venus and the models for their formation are briefly reviewed, and tests that may help to make clear which model best explains the plateau-shaped highlands are considered.