A mélange is a chaotic mixture of rocks of different types and ages, often found in subduction zones and formed by the mixing of sediments, oceanic crust, and mantle material during tectonic processes. Mélanges are important in understanding the processes of subduction, accretion, and tectonic mixing.
Reference: Cowan, D. S. (1985). “Structural Styles in Mesozoic and Cenozoic Mélanges in the Western Cordillera of North America.” Geological Society of America Bulletin, 96(4), 451-462.