New constraints on the New Zealand-South Fiji Basin continent-back-arc margin

New cruise results indicate that the New Zealand-South Fiji Basin margin co mprises a volcanic plateau, separated from the continent by sedimentary bas ins (floored by metamorphic rocks and an allochthon containing Cretaceous o phiolites). Seaward lies undisturbed oceanic crust. The plateau began to fo rm in the Early Miocene after the allochthon was obducted (in the Aquitania n). The oceanic crust of the South Fiji basin is contiguous with that of th e plateau, which in turn indicates that the South Fiji Basin in this region is of Miocene rather than Oligocene age as commonly thought. The tectonic history is perforce that of a Pacific subduction zone replaced by a back-ar e transform margin containing an enormous volume of volcanic material. (C) 2000 Academie des sciences/Editions scientifiques et medicales Elsevier SAS .