A three-plate kinematic model for Lau Basin opening

We present revised compilations of bathymetry, magnetization, acoustic imag ery, and seismicity data for the Lau Basin and surrounds. We interpret thes e data to more precisely locate the plate boundaries in the region and to d erive a three-plate kinematic model for the opening of the Lau Basin during the Brunhes chron. Our tectonic model includes the Niuafo'ou microplate, w hich is separated from the Australian Plate along the Peggy Ridge-Lau Exten sional Transform Zone-Central Lau spreading Center and from the Tongan Plat e along the newly discovered Fonualei Rift and Spreading Center. Our model shows that Australia-tonga plate motion between 15.5 degreesS and 19 degree sS is partitioned across the microplate, and it resolves th former apparent conflict between geodetic versus seafloor spreading velocities. Regionally , this implies that the angular rate of opening of the Lau Basin has been f aster than that of the Havre Trough to the south and that the rapid current rates of Pacific subduction at the Tonga Trench (similar to 240 mm/yr at 1 6 degreesS) have been sustained for at least 0.78 m.y.