Constraining the Depth of Magma Reservoirs on Venus

Abstract

The surface of Venus is dominated by volcanic materials and hundreds of volcanic edifices can be found across the planet [1]. The largest among these are the so-called coronae, i.e., circular to elongated features surrounded by concentric fractures that reach diameters of hundreds of kilometers, and large shield volcanoes (100-1000 km diameter); in addition thousands of small shield volcanoes (few tens of kilometers in diameter) pepper the Venusian surface. Such a large and widespread volcano population suggests the presence of a significant number of subcrustal/crustal magma reservoirs formed by magmatic upwelling. In order to produce the buoyancy necessary to mobilize magma, the energy available to the system needs to reach a critical value. When this condition is met, a gravitational instability occurs and leads to the vertical spread of material. The Rayleigh Taylor gravitational instability theory can be used to draw a relationship between the spacing of volcanic structures and edifices at the surface and the depth of the magmatic reservoirs beneath the volcanic fields. This analysis has been applied to volcanic clusters at several locations on Earth such as the Newer Volcanic Province in Southern Australia [2] and the Main Ethiopian Rift [3]. Assuming that the Rayleigh Taylor instability theory applied to coronae and volcanic fields on Venus, we use this approach to identify the depth of magma source regions that fed, and perhaps still feed, these features.