Campagne Seapso 3: Structure et evolution du bassin Nord-Fidjien

The North Fiji Basin (NFB) is a shallow oceanic basin, with depths between 2000 and 4000 m, which lies between latitude 10 degree and 25 degree South and longitude 170 degree and 180 degree East. Situated at the boundary of the Indo-Australian and Pacific plates, the NFB stands between two subduction zones of reverse polarity: the New-Hebrides subduction on its western side and the Tonga. The aim of the Seapso 3 cruise of N.O. Jean Charcot (December 1985), was to delineate the recent spreading location in the North Fiji Basin, and to observe possible associated hydrothermal manifestations. For that we first have performed a large scale bathymetric and geophysical survey and then a detailed survey (complete coverage Seabeam) on two boxes. Finally, rocks sampling and hydrocast have been carried out along the axis

Campagne Seapso 4: Etude morphostructurale de la ride de Valufa dans le bassin de Lau

The Lau Basin lies between the Lau and Tonga ridges and extends over more than 1000 km. Its width decreases from 300 km near 16 degree S to less than 100 km near 24S. It is an actively spreading oceanic back-arc basin created in the Plio-Pleistocene the Tonga Trench. The part of the Valu Fa ridge North of 22 degree S was investigated during the Seapso 4 cruise of R/V Jean Charcot in Jan 1986 and complementary data were obtained during the Papnoum transit (Apr 1987). The techniques used included multibeam bathymetry, single-channel seismic reflection, magnetic and gravity field measurements

Accrétion océanique et déformation dans la partie méridionale du bassin Nord-Fidjien: résultats préliminaires de la campagne océanographique SEAPSO III du N.O. Jean-Charcot (décembre 1985)

Seismic, Seabeam, magnetic and gravimetrie surveys in the southern part of the N-Fiji basin were conducted during the SEAPSO LEG III Cruise. The active spreading axis was recognized between 17°30'S and 21°S. It consists of a continuous N-S Ridge cross-cut by transverse directions oriented N25 and N45. North of 17°30'S, the spreading System is more complex due to the existence of a possible triple junction located around 15° S. The eastern part of the N-Fiji basin, west of Viti Levu is mostly characterized by alternating highs and deeps (<4,000 m). This area must be regarded no more as a spreading center, but as complex boundary suffering transverse tectonics.La mission SEAPSO III a permis de localiser une zone d'accrétion active, d'orientation méridienne et pratiquement continue entre 17°30'S et 21° S. Des accidents transverses, qui encadrent ou recoupent cette dorsale, s'orientent autour de deux directions principales N25 et N45. Au Nord de 17 30'S le système d'accrétion, beaucoup plus complexe, annonce la triple jonction reconnue aux alentours de 15" S. La partie orientale du bassin Nord-Fidjien (à l'Ouest de l'île de Viti Levu) est caractérisée par l'alternance de zones hautes et de dépressions dont certaines dépassent 4000 m de profondeur. Il s'agit d'une zone complexe de déformations liées à des accidents cisaillants transverses