Plume Penetration into Venusian Lithosphere and the Origin of Coronae.

With the absence of global plate tectonics, mantle plumes and related gravitational potential variations are generally thought to be driving Venusian tectonics. The circular volcano-tectonic corona structures are perhaps the most profound surface manifestations of these mantle plume upwellings, yet their origin remains enigmatic and possibly non-unique.

Here, we assess the origin of coronae on Venus by the interaction between a thermal mantle plume and Venusian lithosphere using 3D thermomechanical viscoplastic models with the finite-difference code I3ELVIS. Our results reveal several plume-lithosphere interaction regimes that yield corona-like structures at the surface. They depend on the plume buoyancy and the strength of the lithosphere and crust. Our results imply that a mantle plume is able to pierce through the Venusian lithosphere when the plume is sufficiently buoyant and the plate is weak enough (under the condition of plume-induced magmatic weakening). When temperature at the moho is high (>1100 K), the lithosphere at the plume margin is weak and delaminates as lithospheric drips. Alternatively, a stronger lithosphere and thinner crust form an ephemeral, retreating subduction slab at the plume margin, that eventually breaks off. Suction above downwelling drips or subducting slabs produces a trench and outer rise bounding the corona interior, and mantle plume penetration leaves behind a thinned crust. The isostatic response to these plume- and drip-induced crustal thickness variations results in a final topographic inversion into an outer rim and inner depression. If the plume cannot penetrate the lithosphere, it underplates and forms an elevated dome or plateau at the surface. The results show that coronae with rims are only produced by the mantle plume penetration into the Venusian lithosphere, and their common occurrence indicate that most plumes are able to penetrate at least partially into the Venusian lithosphere.

Our results shed light on how different corona morphologies represent different stages in evolution, but may also represent different plume-lithosphere interactions. The outcomes of our numerical experiments agree with natural data and are applicable for assessing individual coronae on Venus as well as studying the planets', and possibly Early Earths', geodynamic behavior.