Crustal and Lithospheric Structures Beneath an Ophiolite Nappe, Southern New Caledonia, Southwest Pacific

To understand ophiolite emplacement mechanisms in New Caledonia, southwest Pacific, we image crustal and lithospheric structures beneath southern Grande Terre, using seismic waveform data from a network (ITOPNC) of permanent and temporary stations (October 2018–November 2019). Surface wave dispersion indicates a 1–2 km thick ophiolite nappe on top of sedimentary basins beneath the east and west coasts, and basement rock in the center of the island. A 1D velocity model derived from local earthquakes has high Vp of 5.5–6.0 km/s beneath the ophiolite nappe. Vp is 7.4 ± 0.2, 7.9 ± 0.3, and 8.1 ± 0.2 km/s at depths of 27–31, 31–35, and 35–40 km, respectively. Receiver function imaging reveals an upper‐lower crust boundary at 12 km depth beneath the center of the island, but this rises eastward to near the surface at the eastern edge of Lake Yate. The base of the crust is sub‐horizontal at 27–30 km depth beneath western and central parts of the island, and shallows to <10 km near the east coast. A conversion imaged at 20 km depth beneath the east coast deepens westward to 65 km and is interpreted as a fossil subduction zone. The low (<4°) taper angle of the ophiolite requires it to have a weak base during emplacement. The source of the ophiolite was east of the coast, where the Moho beneath eastern Grande Terre projects to the surface. Eocene subduction beneath Grande Terre was west‐dipping and the ophiolite can be classified as Cordilleran in nature, that is, low‐density rocks within the hanging‐wall drove uplift and emplacement.