Processes of formation and evolution of mountain belts on Venus

Orogenic belts in Western Ishtar Terra, Venus, rise up to 11 km in elevation and have been interpreted to be sites of crustal shortening resulting in localized crustal thickening and local changes in thermal gradient. Airy isostasy models imply crustal thicknesses in excess of 45 km. We explore the range of conditions in the mountain ranges linked to variations in crustal thickness and thermal gradient. On the basis of the high topographic elevations and evidence for crustal shortening and thickening, we interpret the thermal gradients to be less than the values of 15-25 K/km estimated for low-lying plains regions. High Venus surface temperatures enhancing crustal detachment and gravity sliding and basalt-eclogite phase changes in the deep mountain roots are likely to dominate the topographic evolution of mountain belts on Venus. As a test of this hypothesis, if evidence for early volcanism associated with crustal thickening can be found in the Magellan data, then low strain rates and high thermal gradients are predicted throughout orogenesis. A lack of early volcanism would indicate high strain rates and low thermal gradients.