Mid-ocean ridge and ocean island basalts (MORB, OIB)
MORB are the basalts of mid-ocean ridges, derived from the depleted upper mantle; OIB are those of ocean islands (Hawaii, Canaries, Réunion), derived from a more heterogeneous mantle. They are the reference for the isotopic composition of the mantle.
Composition
Tholeiitic (MORB) or alkaline (OIB) basalts; for example δ7Li about +4 ‰ and δ186/184W about +0.085 ‰.