Ocean crust is basaltic with uniform p wave velocities.
Continental crust varies in p wave velocities both laterally and vertically. Mantle is bulk of Earth - Moho seems to be chemical change rather than just a phase transition. Rift basalts leave depleted mantle peridotites. Subducted basalts are turned into eclogite which may persist in the mantle. Some may generate island arc and Andean volcanics.