La synthèse des données de bathymétrie et les nouveaux résultats de sismique réflexion (1987) issus de travaux le long de la marge occidentale de la Nouvelle-Calédonie sont présentés ici. Les données de bathymétrie mettent en évidence l'existence de plusieurs domaines tectoniques répartis le long de la marge entre 180 et 230s ainsi que des structures transverses importantes surtout localisées au nord-est de l'île. Une limite morphologique majeure apparaît la latitude de 210s. Les nouvelles données de sismique réflexion (campagne ZOE 400) permettent de suivre l'évolution des structures du nord vers le sud et montrent l'existence de trois domaines tectoniques entre 200 et 230 S. Dans le domaine central entre 210 et 226, le pied de la marge est caractérise par un glacis de 18 km de large qui est une zone tectonisée. Des structures interprétées comme des plis et des chevauchements apparaissent. Ceux-ci sont ensuite recoupés par une tectonique en extension. En revanche, dans les domaines nord et sud, la zone plissée ne peut pas être clairement suivie. Les failles normales récentes ont débordé le front de déformation vers l'ouest masquant ainsi la série d'écailles et de plis sous la marge. Cette phase compressive a été active depuis le charriage de la nappe ophiolitique a l'Eocène terminal et résulte de mouvements le long d'une frontière majeure située sur le bord ouest de la Nouvelle-Calédonie. Elle a cessé de fonctionner au Miocène supérieur-Pliocène.

A synthesis of bathymetric data and new seismic reflexion results from the western margin of New-Caledonia are presented here. Bathymetric data which have led to a new bathymetric map show evidence of several tectonic domains between 180 and 230s as well as transverse structures especially in front of the eastern part of the island. The margin falls steeply into the New Caledonia basin which is more than 3 500 m deep and which opened between Upper Cretaceous and Paleocene. A morphological limit appears around 210s at the transition between 1- a northern area where an 110 mean slope joins a marginal trench and 2- a southern area where a milder mean slope joins a continental glacis. These areas are locally intersected by transverse structures. New seismic reflexion data was obtained during ZOE 400 cruise (March 1987). Fourteen N400 E seismic profiles were performed across the western margin of New Caledonia which has been divided into three domains between latitudes 200 and 230s. In the central domain, between 210 and 21050’ S the lower part of the margin is characterized by a gently westward glacis slope. This 18 km-wide glacis is a tectonic zone. By analogy with Caribbean examples (MASCLES, 1986) and because of evidence of recent compressive tectonics on land (COUDRAY 1969; COUDRAY et al., 1972). we are able to interpret deep structures as being related to a compressive phase despite evidence of superficial slumps. Some demonstrative profiles show an upper undeformed sequence overlying a thick unconformed folded and westward thrusted sequence. Synclines, anticlines and overthrusts can be seen on all profiles and the folded sequences show lower strains toward the upper part of the sequence. This suggests an uninterrupted compressive phase during sedimentary deposits. The study of seismic data correlated with Deep Sea Drilling Project (D.S.D.P.) results from holes ZOG, 208 (leg. 21) and 587 (leg. 40) shows that these compressions have been active since the obduction of peridotites ín the late Eocene and result from large scale motions along side the western margin of NC. The end of this compressional event is recent, Upper Eocene to Pliocene, probably around 5 MY. In the northern and southern domains, the folded area cannot be clearly followed in spite of little strain. Recent normal faulting could have overflown the thrust front westward, hiding folds and thrusts under the margin. By contrast, in the central domain, extensional tectonics stay at the back of the thrust front, so that folds and thrusts can be seen. Morphology and study of seismic data around the western NC margin suggest an eastward-dipping fossil subduction zone with a free edge between NC basin bedrock and the island of NC (Tisseau, 1979). More recently, seismologic teleseismic studies (pers. comm. Reignier. 1987) have shown the evidence of the NC substratum dipping under the Noumea peninsula up to GO km in depth. Some authors considered that this plate boundary was born after the opening of the NC basin and that it was active during obduction. Because there is no clearly defined volcanic arc on land we consider that this hypothesis must be carefully considered.