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.

To cite this version:Dominique Cluzel, Sébastien Meffre, Pierre Maurizot, Anthony J. Crawford. Earliest Eocene (53 Ma) convergence in the Southwest Pacific; evidence from pre-obduction dikes in the ophiolite of New Caledonia.. Terra Nova, Wiley-Blackwell, 2006, 18 (6)

[1] Amphibolite lenses that locally crop out below the serpentinite sole at the base of the ophiolite of New Caledonia (termed Peridotite Nappe) recrystallized in the high-temperature amphibolite facies and thus sharply contrast with blueschists and eclogites of the Eocene metamorphic complex. Amphibolites mostly display the geochemical features of MORB with a slight Nb depletion and thus are similar to the youngest (Late Paleocene-Eocene) BABB components of the allochthonous Poya Terrane. Thermochronological data from hornblende ( 40 Ar/ 39 Ar), zircon, and sphene (U-Pb) suggest that these mafic rocks recrystallized at $56 Ma. Using various geothermobarometers provides a rough estimate of peak recrystallization conditions of $0.5 GPa at $800-950 C. The thermal gradient inferred from the metamorphic assemblage ($60 C km À1), geometrical relationships, and geochemical similarity suggest that these mafic rocks belong to the oceanic crust of the lower plate of the subduction/obduction system and recrystallized when they subducted below young and hot oceanic lithosphere. They were detached from the down-going plate and finally thrust onto unmetamorphosed Poya Terrane basalts. This and the occurrence of slab melts at $53 Ma suggest that subduction inception occurred at or near to the spreading ridge of the South Loyalty Basin at $56 Ma.Citation: Cluzel, D., F. Jourdan, S. Meffre, P. Maurizot, and S. Lesimple (2012), The metamorphic sole of New Caledonia ophiolite:40 Ar/ 39 Ar, U-Pb, and geochemical evidence for subduction inception at a spreading ridge, Tectonics, 31, TC3016,

Volcanism of Late Cretaceous–Miocene age is more widespread across the Zealandia continent than previously recognized. New age and geochemical information from widely spaced northern Zealandia seafloor samples can be related to three volcanotectonic regimes: (1) age-progressive, hotspot-style, low-K, alkali-basalt-dominated volcanism in the Lord Howe Seamount Chain. The northern end of the chain (c. 28 Ma) is spatially and temporally linked to the 40–28 Ma South Rennell Trough spreading centre. (2) Subalkaline, intermediate to silicic, medium-K to shoshonitic lavas of >78–42 Ma age within and near to the New Caledonia Basin. These lavas indicate that the basin and the adjacent Fairway Ridge are underlain by continental rather than oceanic crust, and are a record of Late Cretaceous–Eocene intracontinental rifting or, in some cases, speculatively subduction. (3) Spatially scattered, non-hotspot, alkali basalts of 30–18 Ma age from Loyalty Ridge, Lord Howe Rise, Aotea Basin and Reinga Basin. These lavas are part of a more extensive suite of Zealandia-wide, 97–0 Ma intraplate volcanics. Ages of northern Zealandia alkali basalts confirm that a late Cenozoic pulse of intraplate volcanism erupted across both northern and southern Zealandia. Collectively, the three groups of volcanic rocks emphasize the important role of magmatism in the geology of northern Zealandia, both during and after Gondwana break-up. There is no compelling evidence in our dataset for Late Cretaceous–Paleocene subduction beneath northern Zealandia.

New Caledonia lies at the northern tip of the Norfolk ridge, a continental fragment separated from the east Gondwana margin during the Late Cretaceous. Stratigraphic data for constraining the convergence that led to ophiolitic nappes being obducted over Grande Terre during the Eocene are both few and inaccurate. To try and fill this gap and determine the onset of the convergence, we investigated the lithology, sedimentology, biostratigraphy and geodynamic context of the Late Cretaceous -Palaeogene sedimentary cover-rock succession of northern New Caledonia. We were able to establish new stratigraphic correlations between the sedimentary units, which display large southwest-verging overfolds detached along a basal argillite series, and reinterpret their interrelationships. The sediments from the Cretaceous-Paleocene interval were deposited in a post-rift pelagic environment and are mainly biogenic with minimal terrigenous input. From the base up, they comprise black organic-rich sulphide-bearing argillite, black chert (silicified equivalent of the argillite), micritic with chert, and micrite rich in planktonic foraminifera. These passive-margin deposits are found regionally on the Norfolk Ridge down to New Zealand, and on the Lord Howe Rise, and were controlled primarily by regional or global environmental factors. The overlying Eocene deposits mark a change to an active-margin regime with distal calciturbidite and proximal breccia representing the earliest Paleogene flysch-type deposits in New Caledonia. The change from an extensional to a compressive regime marks the beginning of the pre-obduction convergence and can be assigned fairly accurately in the Koumac-Gomen area to the end of the Early Eocene (Late Ypresian, Biozone E7) at c 50 Ma. From this period on, the post-Late Cretaceous cover in northern New Caledonia was caught up and recycled in a southwest-verging accretionary complex ahead of which flysch was deposited in a flexural foreland basin. The system prograded southwards until the Late Eocene collisional stage, when the continental Norfolk ridge entered the convergence zone and blocked it. At this point the autochthonous and parautochthonous sedimentary cover and overlying flysch of northern New Caledonia was thrust over the younger flysch to the south to form a newly defined allochthonous unit, the 'Montagnes Blanches' nappe, that is systematically intercalated between the flysch and the obducted ophiolite units throughout Grande Terre. Premiers enregistrements sédimentaires de la convergence pré-obduction enNouvelle-Calédonie: formation d'un complexe d'accrétion à l'Eocène inférieur dans le Nord de la Grande-Terre et mise en place de la nappe des Montagnes Blanches Mots-clés. -Nouvelle-Calédonie, Ride de Norfolk, Paléocène, Eocène, Turbidite, Flysch, Prisme d'accrétion, Bassin d'avant-pays.Résumé. -La Nouvelle-Calédonie est située sur l'extrémité nord de la ride de Norfolk, lanière continentale séparée à partir du Crétacé supérieur de la marge est-gondwanienne. Les données stratigraphiques pour con...