Rocks of the continental crust contain different minerals and each mineral has its own melting point. If the minerals with the lowest melting temperatures are the only ones melted, this is referred to as:

Partial melting

Explanation: Partial melting occurs when the temperature is high enough to melt some of the materials that make up a rock but not all. This happens because a rock is not made up of a single material but different materials which have different melting points.  

As the molten or melted rock cools down it crystallizes in a process known as fractional crystallization and this is how igneous rocks are formed.