AbstractThe mid‐Tertiary blueschists, eclogites and eclogitic gneisses of northern New Caledonia are the products of four phases of regional metamorphism and deformation (D1–D4). Omphacite, lawsonite and Mn‐rich garnet isogradic surfaces were developed during the second deformation (D2) under prograde pressure and temperature conditions. Subsequent deformations (D3–D4) folded these D2isogradic surfaces. However, within the P‐retrograde, T‐prograde metamorphic environment of the D4phase, omphacite altered to albite and chlorite; as a result, a late‐stage sub‐horizontal isogradic surface developed for omphacite‐out where this mineral preserved as relics within syn‐D4albite porphyroblasts. Other minerals that crystallized for the first time (epidote) or had rim additions (almandine phengite) during D4, also form nearly horizontal isogradic surfaces. Porphyroblastic garnet and albite contain inclusion trails, which allow their microstructural development and crystallization of the matrix to be traced from D2to D4.Late syn‐D4the temperature increased markedly in association with an extensive exothermic decarbonation, even though the rocks were in a state of pressure retrogression. This caused considerable neocrystallization, recrystallization and growth of mattix and porphyroblasts such that, although S2foliation crenulated by D3and D4is readily observable, almost all signs of stored strain due to D3and D4have been removed, and the deeper schists and eclogitic gneisses superficially appear to have undergone a drastic annealing recrystallization, po