Geology and kinematics of the Niuafo'ou microplate in the northern Lau Basin

We present a revised three-plate kinematic model for the Lau Basin, focusing on new interpretations of the geologic characteristics of the Niuafo'ou microplate boundaries. It builds upon the three-plate model by Zellmer and Taylor (2001) while resolving some geologic discrepancies in that model. Along the southern branch of the Mangatolu Triple Junction and the Fonualei Rift and Spreading Center, which together form the Niuafo'ou-Tonga plate boundary, our model predicts slow to ultraslow opening rates (similar to 32-8mm/yr southward), consistent with axial morphology and magnetic profile modeling. Our interpretation of the seafloor magnetization pattern and flank morphology along the Central Lau Spreading Center (CLSC) indicates that opening rates along the Australia-Niuafo'ou boundary are higher than predicted in the previous model, thus compensating for slower rates along the Niuafo'ou-Tonga boundary. Lastly, we show geologic evidence that Peggy Ridge (PR), interpreted previously as an active transform fault and therefore a strong azimuthal constraint on Niuafo'ou plate motion, is inactive and that the active plate boundary is the adjacent Lau Extensional Transform Zone, extending from the CLSC to its intersection with the Northwest Lau Spreading Center. The removal of the PR azimuthal constraint allows us to determine an Euler pole for Australia-Niuafo'ou opening that satisfies three-plate closure criterion and develop a geologically consistent model of Lau Basin kinematics. While the final model focuses on constraining current plate velocities assuming rigid plate Eulerian rotations, the geologic analyses presented herein also provide insight into long-term basin evolution, which appears to involve significant nonrigid plate kinematics.