It has long been suggested that Earth's mantle contains several different compositional reservoirs, including an
ancient more - primitive reservoir at the lowermost mantle, recycled
oceanic crust and depleted background mantle.
As a result, mantle plumes entrain a variable combination of relatively young
oceanic crust directly from the subducting slab, older
oceanic crust that has been stirred with
ancient more primitive material and background, depleted mantle.