All coronae are not equal: which ones can be due to a mantle plume ?

Coronae are quasi-circular features, usually associated with faulting and volcanism, that have been observed so far only on Venus Surface. They have been proposed to form through a number of processes: mantle plumes, small-scale upwellings or downwellings, delamination, melting, or some combination of these processes. At least 500 coronae have been identified so far, ranging in size from 50 to 2600 km, with a mean diameter of 250 km. The aim of this work is to determine which ones could be due to a mantle plume.

We combine new laboratory experiments on the generation of hot thermal plumes in a convecting mantle with already published data, to determine scaling laws on the number, spacing and size of plumes that can be generated in a convecting Venus mantle, as well as the plumes’signatures when they reach the lithosphere (size of impact, hot temperature anomaly). These depend very strongly on the mantle viscosity structure and local or global layering. 

Our results suggest that mantle plumes coming directly from the bottom of the mantle could be responsible for coronae with diameters in the range 400-1200 km. Smaller coronae would need at least a second level of plume generation at the mantle transition zone or in the lithosphere (for the smallest). Interestingly enough, Artemis coronae seems too large to have been formed as it is today by a mantle plume impact. However, the occurence of plume-induced roll-back subduction could have been sufficient to enlarge the coronae to its present-day size.