Inception and Plate Evolution of the Lau Back‐Arc Basin From Plate Boundary Refinements

Abstract Back‐arc basins are important settings for crustal growth that form in response to both near and far‐field tectonic influences. To better understand the processes that control back‐arc basin initiation and evolution, we present a refined model of the kinematics of opening of the Lau Basin, embedded in a global plate model. The model, which runs from 10 Ma to the present, includes three previously unrecognized paleoplates, five microplates and 10 active spreading centers. Collision of the Ontong Java Plateau with the active Vitiaz arc between 25 and 15 Ma blocked subduction of the Pacific Plate and resulted in the formation of a Subduction‐Transform Edge Propagator, or STEP fault, along the Vitiaz Trench. Fragmentation and rotation of the Vitiaz arc crust and the formation of new intrabasinal transform structures such as Peggy Ridge were fundamental in promoting back‐arc rifting. Our model suggests that Peggy Ridge was originally an arc‐parallel extensional fault, reactivated between 7 and 5 Ma as a strike‐slip fault that allowed initial opening of the back‐arc basin and propagation of early rifting into the southern Lau Basin. Multiple drivers, in addition to the dominant control of slab rollback, initiated this rapid change in basin opening, including transcurrent structures in the northern Lau Basin. As a result, the evolution of the basin was highly asymmetric and non‐linear, in contrast to previously‐proposed models. The model strongly supports upper plate processes as important drivers of back‐arc basin development, including collisions, STEP fault formation, forearc extension, fault propagation and block rotation.