Hikurangi Plateau

Hikurangi Plateau
Name	Hikurangi Plateau
Type	Large igneous province
Location	Southwest Pacific Ocean
Coordinates	36°S 178°E
Area	~600,000 km²
Depth	500–2,000 m
Country	New Zealand

Hikurangi Plateau is a large igneous province and oceanic plateau located east of North Island and north of South Island in the southwest Pacific. It is a major Cretaceous volcanic feature that interacts with the Kermadec Trench, the Hikurangi Trench, and the Pacific Plate margin adjacent to New Zealand. The plateau influences regional seismicity and subduction zone processes and has been the focus of multidisciplinary studies by institutions such as GNS Science, the National Institute of Water and Atmospheric Research, and international marine programs including the Ocean Drilling Program and the Integrated Ocean Drilling Program.

Geology

The plateau is interpreted as a fragment of an extensive Cretaceous large igneous province related to magmatic events contemporaneous with the Ontong Java Plateau and the Manihiki Plateau. It overlies older Pacific Plate basement and is bounded by major structural features including the Kermadec Ridge, the Chatham Rise, and the Hikurangi Margin. Regional geophysical surveys using multibeam echosounder systems, seismic reflection profiles, and gravity and magnetic anomaly mapping have delineated thickened crust and high-velocity bodies characteristic of flood basalt provinces. The plateau's distribution affects sediment routing from the Wairarapa Basin, the Taranaki Basin, and the Great South Basin.

Formation and Geological History

Geochronological work yields emplacement ages in the mid- to Late Cretaceous, commonly cited around 120–90 million years ago, contemporaneous with breakup events involving the Greater India and the Australasia plate margin reconstructions. Plate reconstructions link emplacement to mantle plume activity associated with the formation of the Manihiki, Ontong Java, and Magellan large igneous provinces. The plateau is thought to have rifted, fragmented, and translated by motions along the Pacific Plate and the former Phoenix Plate, with later interaction during the opening of the Tasman Sea and the drift of Zealandia.

Tectonic Setting and Subduction

The eastern margin of the plateau is currently being subducted beneath the North Island along the Hikurangi Trench, producing the Hikurangi Subduction Zone and contributing to the regional seismic hazard characterized by events like the Kaikōura earthquake (2016) and the recurrent megathrust earthquakes known from paleoseismic studies in the Wairarapa and Hawke's Bay regions. Subduction of thickened plateau crust affects coupling on the plate interface beneath the Wellington and East Cape segments, influences the locus of volcanism in the Taupō Volcanic Zone, and modifies the geometry of the Kermadec Arc and the Tonga–Kermadec Ridge. Geodetic networks such as GeoNet monitor deformation related to this tectonic interaction.

Structure and Composition

Seismic tomography and wide-angle refraction profiles show crustal thicknesses significantly greater than normal oceanic crust, with high-velocity lower crustal bodies interpreted as dense gabbro-dominated intrusions or underplated material. Geochemical analyses of dredged and drilled basalts indicate low- to high-Ti basalt suites with isotopic signatures linking them to plume-related sources similar to those inferred for the Manihiki Plateau and the Ontong Java Plateau. The plateau includes uplifted plateaus, seamount chains, and buried volcanic constructs overlain by pelagic and hemipelagic sediments, with sediment distribution influenced by regional currents such as the East Auckland Current and by submarine canyons like the Hawke's Bay Canyon.

Paleoenvironment and Volcanism

During and after emplacement, the plateau would have affected regional ocean circulation, primary productivity, and sedimentation patterns across the South Pacific in the Cretaceous. Extensive magmatism likely induced transient changes in atmospheric composition and climate through greenhouse gas and aerosol release similar in principle to other Large Igneous Provinces implicated in global environmental perturbations such as those associated with the Deccan Traps and the Siberian Traps. Fossil assemblages preserved in coeval marine sediments recovered near the plateau provide context for Cretaceous marine biotic distribution and biogeographic provinces that include taxa studied from deposits in West Antarctica, Antarctic Peninsula, and Australia.

Biological and Ecological Significance

Topographic relief of the plateau and associated features such as the Kermadec Ridge creates habitats for diverse deep-sea communities including cold-water corals, sponges, chemosynthetic communities, and pelagic predators documented by expeditions from research vessels like RV Tangaroa and RV Sonne. The area overlaps with exclusive economic zones of New Zealand and with marine protected area considerations explored by the Department of Conservation and regional councils. Biological sampling campaigns by the National Institute of Water and Atmospheric Research and international collaborators have recorded species with affinities to faunas from the Kermadec Islands and the Chatham Islands.

Exploration and Research History

Systematic study began with mid-20th century marine surveys by institutions including the Commonwealth Scientific and Industrial Research Organisation and later intensified with participation in global drilling initiatives such as the Ocean Drilling Program, Integrated Ocean Drilling Program, and International Ocean Discovery Program. Key contributions come from New Zealand institutions like GNS Science, universities including Victoria University of Wellington and University of Otago, and international partners from United States, Japan, and Germany. Recent research integrates seismic imaging from programs like Seafloor Imaging campaigns, multidisciplinary oceanographic cruises, and modeling studies published in journals such as Nature Geoscience, Geology, and Earth and Planetary Science Letters.

Category:Large igneous provinces Category:Geology of New Zealand Category:Oceanic plateaus