The geology of the venusian plains

Abstract

A large fraction of the venusian surface is formed by rolling plains, whose altitude is typically 1 to 3 kilometers under the planet mean radius. The plains’ most interesting features are volcanic structures, winkle ridges and tectonic belts. The volcanic activity has generated huge lava fields that have inundated almost all the planet’s surface concealing any previous features that possessed. This activity has resulted in the formation of the plains, volcanic buildings whose morphologies are very similar to terrestrial analogs and that usually appear in groups of several individuals, although sometimes they are isolated; may well find a shield volcanoes, slag and tephra cones and domes among others. Wrinkle ridges are interpreted as resulting from failure of the crust under compression. Tectonic belts are linear zones of concentrated deformation hundreds of kilometers long, tens of kilometers wide, which include thrusted anticlines, grabens, tight folds, and strike-slip fractures. The combination of these structures makes up belts with different kinematics: extensional belts mainly characterized by grabens, thrust and fold contractional belts, and strike-slip shear belts usually defined by the en echelon disposition of folds (transpression) or grabens (transtension). Another important characteristic of the ridged plains, indicative of a crust excess density, is that the majority of them exhibits a geoid negative anomaly and are far from isostatic equilibrium. Whereas tectonic belts have received an ample attention, there is not consensus on theirorigin has not been reached. Several hypotheses have been proposed, for example excess density (deduced from geoid anomaly) causing compression through the drag of vertical traction and inducing plains downwelling, push of the geoid highs over low-standing terrains, or crustal delamination. Thus, venusian plains are useful keys for the understanding of the evolution of Venus.