UNFOLDING THE SUBDUCTING PLATE IN THE CENTRAL NEW HEBRIDES ISLAND-ARC- GEOMETRICAL ARGUMENT FOR DETACHMENT OF PART OF THE DOWNGOING SLAB

In the central part of the New Hebrides island arc a sizable gap exist s in the seismic activity. Seismic observations in the zone of the gap have been previously interpreted as either related to a detachment of part of the downgoing slab or associated with a continuous slab. We g ive a geometrical argument which, added the seismic observations from these previous studies, adds one step in favor of the detachment hypot hesis. After unfolding the downgoing plate and restoring it to its ini tial state, using a 3D balance technique, we show that the gap can be filled with three pieces. Two of these pieces are seismic zones locate d beneath the seismic gap and the third one is a deep (550 - 650 km) s eismic zone located about 200 km north-east of the arc. These three pi eces could be detached parts of the subducting plate.