Ocean floor subducts under continents because the ocean floor is softer and the crust in here is with lesser density and thickness, while the continents are harder because their crust is thicker and has bigger density. So when they collide, the softer ocean floor is pushed downwards by the harder continental crust.
They are formed by the confining heat and pressure that they derive from the physical and chemical alteration of the igneous and the sedimentary rocks. The rocks undergo es a regional metamorphism and involve a larger body of rocks that occur over a wider area.
Typically are associated with mountain building and orogenic events and display a distinct band of mineral and colors, which is called foliation.
<u>The force that drives these rocks to the various forms are those of the plate tectonics and includes the separating rides and the subducting zone along wit the continental collisions.</u>
