How can sedimentary rock change into metamorphic rock?

Answer 1

Many ways, really. For example, a continental plate may be submerging underneath another continental plate (a boundary interaction often associated with volcanoes), and in the process, that continental plate that is being submerged, often the ocean floor, changes into metamorphic rock, and if subjected to enough pressure and heat, may become igneous. Or, if two continental plates collide where one plate used to be ocean floor, such as with the Himalayan Mountains, the two plates would jam together. In between these plates, there may be enough heat and pressure to change the sedimentary rock into metamorphic rock.