Linking active margin dynamics to overriding plate deformation: Synthesizing geophysical images with geological data from the Norfolk Basin

[1] The Tonga-Kermadec subduction system in the southwest Pacific preserves a series of crustal elements and sediments which have recorded subduction initiation, rift, and back-arc basin formation. The Norfolk Basin is the farthest landward of all back-arc basins formed in the Tonga-Kermadec region and may preserve the earliest record of subduction initiation regionally. For the Norfolk Basin, we use a set of multibeam bathymetry, magnetic, and seismic reflection and refraction data to constrain basin structure and the mode and timing of formation. A structural interpretation reveals a two-stage tectonic evolution: (1) a convergent tectonic regime until 38–34 Ma, alternatively related to island arc collision or subduction initiation, and (2) lithospheric extension after 34 Ma. These observations may help to constrain mechanical models that predict rapid extension following convergence of the overriding plate during subduction initiation or arc reversals.