Venus' current surface temperature is around 740K (about 500K higher than a Blackbody would be at its orbital distance from the sun, due to its thick atmosphere). That's really hot, but not enough to actually melt the surface.
If you had a similar planet with a thick CO2 atmosphere at the right distance from its star, could you end up with a greenhouse effect that is so high that the rocks on the surface would melt? (you'd need a temperature of about 1400-1500K to melt Basalt)
I'm wondering if that would be a stable situation, or if there's some process by which the atmosphere would evaporate away (thus reducing the greenhouse effect, thus reducing the temperature) or some other process would occur to make it unstable, or stop that from happening at all?