PRODUCTION OF SMALL VOLCANOS IN THE SUPERSWELL REGION OF THE SOUTH-PACIFIC

We use Sea Beam swath bathymetry and wide beam profiler data to invest igate the production of small (50-700 m high) volcanoes in the region of the Superswell 1! in French Polynesia. Seamount population paramet ers are estimated for three study regions. We find that seamount abund ances increase threefold going southward across the Marquesas fracture zone, the inferred northern boundary of the Superswell. In addition, we document that south of the Marquesas fracture zone, seamount abunda nces, on average, are equally as high on young crust (0-18 My) generat ed at the East Pacific Rise (9-degrees-22-degrees) as on the adjacent Superswell region (approximately 20-60 My old crust). The fact that se amount abundance estimates are the same in the two regions south of th e Marquesas fracture zone leads to an uncertainty in whether the seamo unts have been produced by ridge or off-axis processes, and suggests t he following possibilities: (1) processes at the East Pacific Rise hav e produced more small seamounts south of the fracture zone than to the north for the last 60 My, (2) off-axis processes (possibly related to the Superswell) have led to excess seamount volcanism on both the Sup erswell region and the region adjacent to the East Pacific Rise, or (3 ) off-axis seamount production is anomalously high on the Superswell, and the production of seamounts has increased at the East Pacific Rise since 20 My.