An outline of the Geology of New Caledonia; from Permian–Mesozoic Southeast Gondwanaland active margin to Cenozoic obduction and supergene evolution

New Caledonia has provided new impetus and opportunity to gather new field data, harmonise and synthesise already mapped areas, and create geological databases; therefore, knowledge of the geology of New Caledonia has made significant progress.Since earliest Permian time, the age of New Caledonia's oldest rocks (Aitchison et al., 1998), three phases of development have been recognised: Permian-Early Cretaceous, Late Cretaceous-Eocene, and Oligocene-Holocene.The oldest is related to the evolution of the SE Gondwanaland active margin, Mesozoic marginal basin opening and subsequent closure; the second corresponds to the rifting that isolated slices of the older Gondwanaland margin and extends into the Cenozoic convergence that eventually ends with Late Eocene obduction; the third mainly corresponds to the supergene evolution of New Caledonia and involvement of the Australian Plate in the New Hebrides (Vanuatu) subduction zone.This article presents a simplified review of the geological evolution of New Caledonia mainly based upon recently published data.Key for abbreviations: MORB: mid-oceanic ridge basalt; E-MORB: enriched (or undepleted) MORB; OIB: oceanic island basalt; BABB: back-arc basin basalt; IAT: island-arc tholeiite; HP-LT: high pressure-low temperature (metamorphic rocks). New Caledonia in the framework of the Southwest PacificNew Caledonia is located within a complex set of marginal basins and "continental" or volcanic-arc ridges (Figure 1).It is composed of several islands that are parts of the Norfolk and Loyalty ridges.The main island (or "Grande Terre") belongs to the Norfolk Ridge, which is connected southward to the large continental plateau that also bears New Zealand.The Belep Islands to the N and Isle of Pines to the S of the main island also belong to the Norfolk Ridge.In contrast, the Loyalty Islands represent the emerged part of a sinuous submarine ridge (the Loyalty Ridge) that runs more or less continuously parallel to the Norfolk Ridge over more than 1,500 km, from the d'Entrecasteaux Zone (W of Espiritu Santo,Vanuatu) in the N, to the Cook Fracture Zone in the S (Figure 1).Between the Loyalty and Norfolk ridges, the Loyalty Basin is a narrow, 1.5-3 km deep, oceanicThe geological evolution of New Caledonia may be divided into three phases.The Gondwanan phase (Permian-Early Cretaceous), is marked by subduction along the SE Gondwaland margin.At that time, proto-New Caledonia was located in a fore-arc region in which volcanic-arc detritus accumulated; whilst accretion and subduction of oceanic and terrigenous material formed an accretionary complex metamorphosed into the blueschist facies.During the Late Cretaceous-Eocene, marginal rifting isolated New Caledonia, and after a short period of shallow water terrigenous sedimentation associated with minor volcanic activity, only pelagic sediments accumulated.A new NE-dipping subduction appeared to the E of New Caledonia at the Paleocene-Eocene boundary, it generated the eclogite-blueschist complex of northern New Caledonia, consumed the eastern Australian Plate, and eventually ended with Late Eocene obduction when the Norfolk Ridge blocked the subduction zone.Finally, during the post-Eocene phase, New Caledonia definitively emerged; this episode mainly corresponds to prominent regolith development and minor tectonic events that lead to the present morphology and to the development of supergene nickel ores.