this unique style of music is known as yayue, which was classical music being played with multiple dancers.
The accretionary wedge is like the accretionary prism and the definition of that is : *a mass of sedimentary material scraped off a region of oceanic crust during subduction and piled up at the edge of the overriding plate (source : dictionary)* and the formation is when two plates crash and one slides under the other one I believe and sand ad sediment go into the little open space between them that give you a wedge. Hope I helped.