Final answer:
An accretionary wedge is composed of sediments and sedimentary rocks scraped off the subducting oceanic crust at convergent plate boundaries.
Step-by-step explanation:
The material incorporated into an accretionary wedge comes from sedimentary rocks and sediments that are scraped off the subducting oceanic crust as it converges with the overriding plate. This process happens at convergent plate boundaries, where two tectonic plates collide and one plate is forced underneath the other in a process called subduction. The scraped-off materials pile up and deform, creating the accretionary wedge, which is a mass of non-metamorphosed sediments and slightly metamorphosed rocks at the edge of the overriding plate.