A schematic image of subducted oceanic crust inferred from this study. Basalt and harzburgite layers of the oceanic crust accumulate beneath and above the 660 km discontinuity, respectively.

Figure 4: Pressure–temperature diagram showing generalised carbonate phase relations in subducted, carbonated oceanic crust. The melting curves of carbonated basalt at upper mantle and transition zone ...

But its composition can also be inferred from basaltic rocks in the oceanic or continental crust, or from chunks of mantle rock that were caught up in the crust. A compositionally heterogeneous ...