Fitting Northland, New Caledonia and d?Entrecasteaux geology into the Late Cretaceous-Cenozoic Southwest Pacific tectonic framework

Abstract

Late Cretaceous to Cenozoic reconstructions of the Southwest Pacific region show a large degree of discrepancy. Moreover, some do not incorporate the geology of the New Caledonia region, most do not incorporate the geology from Northland, New Zealand, and none incorporates the lithospheric-scale structure from the d?Entrecasteaux zone. A new tectonic model is proposed that incorporates the regional geology from these three regions into the large-scale and well-defined tectonic framework of relative motion between the Australian plate, Pacific plate and Lord Howe Rise microplate. In the new model, the d?Entrecasteaux zone is interpreted as a dextral transform fault. The New Caledonia and Northland regions are interpreted to bear the hallmarks of a former northeast dipping subduction zone with an east dipping subduction segment in between, located west of the Three Kings Ridge. The subduction zone formed at 50-45 Ma, a period when Australia-Pacific relative motion changed from strike-slip to oblique convergence. Subduction was primarily realized by east to southeast-directed anticlockwise slab rollback of the South Loyalty Basin lithosphere and tearing of the slab at the surface along the d?Entrecasteaux zone. The subduction rollback process resulted in formation of the North Loyalty-South Fiji back-arc Basin and induced arc volcanism along the d?Entrecasteaux-Loyalty-Three Kings Ridge-Northland Plateau seamount chain. The final stage of the subduction process resulted in southwest-directed obduction of ophiolites in New Caledonia at 38-34 Ma and in Northland at 25-22 Ma.