Re: Makes sense
A lot of this will boil down (ahem) to how much water is in the Venusian Mantle. Water has a major effect on lowering the temperatures at which rock undergoes partial melting to produce magma. Add a few percent water to the Mantle and the lowest temperature minerals melt and separate from the solid residue. If water is absent, then the high pressures of the Mantle can prevent any significant melting.
The lack of plate tectonics on Venus has been used as an argument that there is very little water in the Venusian interior which means melting is extremely limited compared to what is going on down here.
Magellan's data has raised the possibility that the Venusian interior accumulates heat over hundreds of millions of years until temperatures reach a point where massive partial melting occurs all across across the planet and the whole surface is resurfaced in a very short period of time by catastrophic volcanism. The evidence is that Venus has relatively few observable craters compared to the Earth, Moon and Mars even allowing for its thick atmosphere; but if there are no plate tectonics there should be a long record of major impacts. In this theory the whole of Venus was remodelled at some point between 300 and 500 million years ago.