sentences:  The IBM arc system subducts mid-Jurassic to Early Cretaceous lithosphere, with younger lithosphere in the north and older lithosphere in the south.It is not possible to directly know the composition of subducted materials presently being processed by the IBM Subduction Factory – what is now 130 km deep in the subduction zone entered the trench 4 – 10 million years ago.However, the composition of the western Pacific seafloor-oceanic crust – sediments, crust, and mantle lithosphere – varies sufficiently systematically that, to a first approximation, we can understand what is now being processed by studying what lies on the seafloor east of the IBM trench.