Eocene nephelinite and basanite from the Fairway Ridge, North Zealandia

A widely recognised feature of the continent of Zealandia is its areally-extensive, low-volume, non-hotspot related, Late Cretaceous to Holocene intraplate magmatism. While samples are readily available from onshore regions, the offshore extent of the province, especially in northernmost Zealandia, remains poorly known. In July 2016, the ECOSATII research voyage on the RV Investigator (IN2016T01) recovered c. 240 kg of limestone-cemented volcanic breccias from three dredge sites on the Lansdowne Bank and Fairway Ridge, part of a NW-SE trending bathymetric high near New Caledonia. The breccias are mostly hyaloclastite with clasts of holocrystalline titanaugite ± olivine ± hornblende porphyritic mafic lavas. Whole rock geochemical analyses indicate the lavas are alkali basalt, basanite and nephelinite. Early to Middle Eocene (52.3–43.6 Ma) and Late Pliocene (3.3–2.6 Ma) planktic foraminifera from the breccias provide age constraints on the volcanism. These new samples add to the small but growing collection of compositionally extreme lavas from Zealandia, which result from low-percentage mantle melting beneath stretched and submerged continental crust. The age and location of the lavas suggests a link between volcanism and dynamic mantle disturbances triggered by Eocene subduction initiation.