Three dives in the "Shinkai 6500" submersible were made on the inner (trench wall of the Izu Bonin arc at 32'N in order to sample arc basement and lest models of forearc evolution. Our dives were focused on basement outcrops exposed between 5,500 and 6,500m water depth in a region considered to lack an accretionary wedge. Six samples

were collected and analysed and provided an unexpected result: a distinct mid-ocean ridge basalt (MORB) chemistry unlike any oilier rocks previously sampled In the Izu Bonin arc. These rocks are distinctly different from forearc basement (boninitic) rocks drilled from Site 786 of ODP Leg 125 on the outer arc high just upslope from our dive sites. They are also unlike any of the active arc or backarc volcanic rocks.