Answer:
1. Continental-continental convergence are both <em>continental crust</em> plates.
2. Buoyancy basically means these plates are light float on top of the Asthenosphere.
Explanation:
1. To go a little more into detail, this type of convergence ocurrs when two plates made of continental crust (not oceanic) collide. In the case of ocean-continent convergence, the denser oceanic crust sinks underneath the lighter continental crust.
In this scenario, we have two plates, neither of which want to sink, so instead of going down they just crumple and fold and keep colliding. This collision creates very high mountain ranges such as the Himalaya and usually doesn't contain any volcanic activity because no magma is capable of penetrating through so much crustal material.
2. As for why continental crust is buoyant and doesn't sink has much to do with its composition. Continental crust is made mostly of silicate material. This is very different from oceanic crust which is made of basaltic rocks and is therefore heavier. The term buoyancy refers to the 'floating action' of the continental crust on top of the uppermost mantle.
