Norfolk Ridge bounds the northeastern edge of the continent of Zealandia and is proximal to where Cenozoic Tonga-Kermadec subduction initiation occurred. We present and analyze new seismic reflection, bathymetric and rock data from Norfolk Ridge that show it is composed of a thick sedimentary succession and that it was formed and acquired its present-day ridge physiography and architecture during Eocene to Oligocene uplift, emergence and erosion. Contemporaneous subsidence of the adjacent New Caledonia Trough shaped the western slope of Norfolk Ridge and was accompanied by volcanism. Neogene extension along the eastern slope of Norfolk Ridge led to the opening of the Norfolk Basin. Our observations reveal little or no contractional deformation, in contrast to observations elsewhere in Zealandia, and are hence significant for understanding the mechanics of subduction initiation. We suggest that subduction nucleated north of Norfolk Ridge and propagated rapidly along the ridge during the period 40-35 Ma, giving it a linear and narrow shape. Slab roll-back following subduction initiation may have preserved the ridge and created its eastern flank. Our observations suggest that pre-existing structures, which were likely inherited from Cretaceous Gondwana subduction, were well-oriented to propagate rupture and create self-sustaining subduction.

Key Points

We present new marine geophysical and geological data of Norfolk Ridge located along the northeastern edge of the Zealandia continent

We show that the ridge is not inherited from Cretaceous rifting that led to isolation of Zealandia but from the TECTA Cenozoic tectonic event

Analysis of the structure and evolution of Norfolk Ridge underpins our understanding of tectonic processes of subduction initiation

Plain Language Summary

Plate tectonic theory established and proved that the surface of Earth is composed of rigid moving plates, but it remains unclear how and why these plates sometimes re-configure their boundaries and motions. Subduction zones are places where two plates converge and one plunges deep into the Earth beneath the other one. As the plate sinks, it drags the rest of the plate with it and acts as an engine that “pulls” the plate and drives horizontal motion. This is what drives the dynamics of plate tectonics. How are subduction zones created? This remains an open question, but we know from geological observations that new subduction zones do get created: more than half of all active subduction zones were created after the dinosaurs died out 65 million years ago. We present new observations from northern Zealandia (a submerged continent between New Zealand and New Caledonia) that document how one of the largest subduction zones on Earth, the Tonga-Kermadec system, started.