Under metamorphism,which high heat or pressure is applied to the igneous rock,the igneous rock’s chemical composition or texture will be different from that of it's parent rock and turn into a metamorphic rock.
In your case,an igneous rock would undergo metamorphism where large scale mountain building process take place such as folding and faulting,and the rock would be under very high pressure,hence turn into a foliated structure. The metamorphism is called dynamic or regional metamorphism if you want to know.
For example, an igneous rock,granite, will turn into gneiss under metamorphism in which high pressure take place.
