THE NORTH BANDA SEA (EAST INDONESIA) - AN UPPER MIOCENE BACK-ARC BASIN

Pillow-lavas have been dredged from the deep basement of the North Ban da Sea, during the French-Indonesian Geobandut cruise. They are transi tional basalts and trachyandesites displaying negative niobium and tan talum anomalies similar to those of lavas from back-arc basins. Their K-40-Ar-40 whole rock isotopic ages are 9 and 6.9 Ma respectively. Des pite a large subsidence anomaly, the deep ''oceanic'' basement engaged in subduction beneath Sulawesi Island is thus not a trapped piece of Indian Ocean but an Upper Miocene back-arc basin floor.