Plume-induced subduction: from laboratory experiments to Venus large coronae

Abstract:

The development of new visualization techniques and the use of complex-rheology fluids open a new area for planetary geodynamic modelling, as observations of surface patterns (i.e. faults, folds, ridges, trenches) can be related to convective instabilities inside the laboratory mantle analog. The rheology of colloidal aqueous dispersions of silica nanoparticles depends strongly on the solid particle fraction, φ_p, deforming in the Newtonian regime at low φ_p, and transitioning to strain-rate weakening, plasticity, elasticity, and brittle properties as φ_p increases. So, as the system is dried from above, a dense skin grows on the surface, akin to a planetary lithosphere. If it is also heated from below, hot plumes develop.

When a hot plume impinges under the skin, it triggers a new mode of subduction: as the upwelling plume material breaks the lithosphere and flows above the denser skin, it forces it to sink. The subduction trenches are localized along the rim of the plumes and strong roll-back is observed. Subduction always occurs along partial circles, a situation very different from the purely viscous case. This is due to the brittle character of the upper part of the experimental lithosphere: it cannot deform viscously to accommodate roll-back and sinking motions. Instead, the plate tears, as a sheet of paper would do upon intrusion. The experiments further suggest that a weaker lithosphere than that present on Earth today is required for such a convective regime.

These experimental observations strongly resemble the association of large coronae with trenches that is observed on Venus. The surface deformation structures and the subsurface density variations predicted by the laboratory agree with radar image observations and subsurface density variations inferred from modeling the gravity and topography data at Artemis and Quetzelpetlatl Coronae. Evidence for geologically recent volcanism at Quetzelpetlatl suggests that subduction may be currently active on Venus.