Question

Which is more buoyant--a continental plate or an oceanic plate? Which would subduct if the two were to collide?

Answer 1

Continental plates contain less dense rocks than oceanic ones, so the continental plates are more buoyant and the oceanic plates will subduct uopn collision.

Explanation:

One result of this is that oceanic floors contain rock that has been mixed with the mantle many times over, so oceanic crust has a chemical composition similar to the underlying mantle -- mostly magnesium-iron silicates or mafic ("magnesium-ferric") rock.

The continents have lighter, felsic rock (so called from their feldspar content) tend to remain physically separated from the underlying mantle, thus perpetuating the differences in chemical composition and density.