Variabilité morphostructurale à l'échelle kilométrique de la dorsale du Bassin Nord-Fidjien : exploration in situ du segment compris entre 18°50S et 19°S

During the STARMER programme the submersibles Nautile and Shinkai-6500 carried out 14 dives on the NS segment of the North Fiji Basin Ridge (Station 14 at 18-degrees-50 S). From structural point of view, two types of morphology appear: in the northern part, the axis is not tectonically well expressed hut the hydrothermal activity is important. in the southern part, a graben structure 150 m wide exists, with both a.fossil and a present-day hydrothermal activity. The station 14 shows a morphostructural variability of the spreading axis which can be related to the different stages of the volcanic and tectonic cycles. Another station explored at 19-degrees-S, a few kilometres to the south, confirms the fact that different stages of tectonic and magmatic evolution can exist at small scale on the same ridge axis. Over the whole area the lavas are extremely fresh, with predominant lobate lava lakes. They are the record of very recent volcanic activity.