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. Hot spot volcanics seem to tap a deeper and more primitive source.