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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 an

The 2015 VESPA voyage (Volcanic Evolution of South Pacific Arcs) was a seismic and rock dredging expedition to the Loyalty and Three Kings Ridges and South Fiji Basin. In this paper we present 33 40Ar/39Ar, 22 micropaleontological, and two U/Pb ages for igneous and sedimentary rocks from 33 dredge sites in this little-studied part of the southwest Pacific Ocean. Igneous rocks include basalts, dolerites, basaltic andesites, trachyandesites, and a granite. Successful Ar/Ar dating of altered and/or low-K basalts was achieved through careful sample selection and processing, detailed petrographic and element mapping of groundmass, and incremental heating experiments on both phenocryst and groundmass separates to interpret the complex spectra produced by samples having multiple K reservoirs. The 40Ar/39Ar ages of most of the sampled lavas, irrespective of composition, are latest Oligocene to earliest Miocene (25–22 Ma); two are Eocene (39–36 Ma). The granite has a U/Pb zircon age of 23.6 ± 0.3 Ma. 40Ar/39Ar lava ages are corroborated by microfossil ages from associated sedimentary rocks. The VESPA lavas are part of a >3000 km long disrupted belt of Eocene to Miocene subduction-related volcanic rocks. The belt includes arc rocks in Northland New Zealand, Northland Plateau, Three Kings Ridge, and Loyalty Ridge and, speculatively, D’Entrecasteaux Ridge. This belt is the product of superimposed Eocene and Oligocene-Miocene remnant volcanic arcs that were stranded along and near the edge of Zealandia while still-active arc belts migrated east with the Pacific trench. Key Points A major pulse of 25–22 Ma volcanism is documented on the Loyalty and Three Kings Ridges, southwest Pacific Ocean The ridges are part of a more than 3000 km long belt of Eocene to Miocene remnant volcanic arcs, stranded along the edge of Zealandia With care in sample selection, and petrological work, meaningful Ar/Ar ages can be obtained from altered and/or very low-K submarine basalts Plain Language Sum