Formation of coronae topography and fractures via plume buoyancy and melting

Coronae are volcanic -tectonic features seemingly unique to the surface of Venus. As such they offer potential insights into differences in geodynamic processes on Venus and Earth. Largely due to limitations in processing power and computational complexity, models of corona formation generally ignore the effect of melt and magmatism despite the presence of volcanic features like domes and lava flows. Here we present a new model of corona formation integrating visco-plastic rheology with two-phase flow melt migration. Additionally, we model brittle failure of surface material, viscous flow of partially molten material at depth, and cracking of solid rock from fluid pressure in one model. The model consists of a two-dimensional half space with a round plume body ascending through an asthenosphere and interacting with a Venusian lithosphere and crust. The size and temperature of the plume body, lithosphere thickness, crustal thickness, and regional strain rate are all varied over 20 model runs. Most models show deflection of the plume as it rises due to the increased viscosity of the base of the lithosphere. As the plume spreads and rises against the base of the lithosphere, melting occurs. Melt rises and accumulates in the lithosphere which supports surface topography. Brittle failure occurs at the surface due to the induced stress of the migrating plume body and rising melt. Increased temperatures and sizes of initial plumes result in larger topographies occurring over smaller timescales. Decreased temperatures and sizes of initial plumes result in smaller topographies over larger timescales. Increased lithosphere thickness generates smaller topographies. Thinner crusts result in more viscous lithosphere and more strain accumulation, creating surface depressions seen in approximately half of real corona. Both thicker crusts and increased regional strain result in lower viscosities at the base of the lithosphere, preventing the deflection of the plume body, which instead rises through the lithosphere relatively unimpeded. The varied model parameters generally result in an evolutionary sequence of topographies and fracture patterns which resemble actual corona, without requiring a collapsing dome to create outer rims, as is often invoked for corona formation via upwelling plumes. Corona rim topography is generally created within 105 and 106 year timescales, while multiple rims or central depressions are generally observed over 106 year timescales. Observed topography is actively supported by partially molten regions in the lithosphere, supporting the notion of an active squishy -lid Venus. These partially molten regions are not centrally located and may provide a source for observed lava flows away from corona centers.