What processes found at a convergent boundary will help form Igneous rocks?
At many convergent boundaries a subduction zone is formed which drives crust down toward the mantle where the rock is melted and turned to igneous rock.
Where an oceanic crust meets a continental crust at a convergent boundary the oceanic crust is subducted under the continental crust. As the oceanic crust is driven down the friction, pressure and heat of the mantle melts the oceanic crust. The melted crust become igneous rock and often comes to surface in volcanos found near the convergent boundary.
The melted crust that doesn't reach the surface becomes igneous granite while the melted crust that does reach the surface becomes lava.
The question unanswered is how thick layers of oceanic crust ends up on the continents when what is observed today is the destruction of oceanic crust at subduction zones, due to convergent boundaries.