Norfolk Ridge

The Norfolk Ridge is about {{cvt|1500|km}} long and is up to {{cvt|100|km}} wide.{{sfn|Collot|Sutherland|Etienne|Patriat|2023|loc=2.2 Physiography and Geology of Norfolk Ridge}} It is between the New Caledonia Trough and Norfolk Basin which has central and southern parts. The Norfolk Ridge emerges above the sea surface at Grande Terre of New Caledonia, Norfolk Island, and part of the northern North Island of New Zealand.{{sfn|Collot|Sutherland|Etienne|Patriat|2023|loc=1 Introduction}} At about 31°S proceeding towards New Zealand, the ridge widens and splits into the Reinga Ridge and West Norfolk Ridge, which are separated by the Reinga Basin.{{sfn|Collot|Sutherland|Etienne|Patriat|2023|loc=2.4 Geology of Northland New Zealand}}

The geology has only been well characterised near Grande Terre, Norfolk Island and near Northland but there is now sufficient evidence from oceanographic studies to revise the former view that the tectonics were just those of the two ends of the ridge. The Norfolk Ridge formed as a depocenter along the eastern margin of Zealandia prior to the Eocene. This formation is suggested to be Mesozoic to early Cenozoic. The ridge itself came into being from then to the Oligocene as part of a spontaneous mode of subduction initiation associated with the Kermadec–Tonga subduction zone. This was previously not understood from the geological studies near Grande Terre and Northland which fitted best an induced subduction initiation model.{{sfn|Patriat|Collot|Roest|Sutherland|2019}}{{sfn|Collot|Sutherland|Etienne|Patriat|2023|loc=7 Conclusions}}

The Norfolk Ridge basement is {{cvt|20| – |25|km}} thick with continental crust characteristics.{{sfn|Collot|Sutherland|Etienne|Patriat|2023|loc=2.2 Physiography and Geology of Norfolk Ridge}} It can be seen as a continuation of the mesozoic basement of Grande Terre (Tremena and Central Chain terranes) through to the Waipapa and Murihiku terranes of New Zealand. There is no evidence of the allochthons that are found in New Caledonia and Northland, except for one limited nappe area on the ridge's eastern flank.{{sfn|Collot|Sutherland|Etienne|Patriat|2023|loc=4.1 Structure of Norfolk Ridge}} The limited rocks dredged include undated andesitic to trachyandesitic lava, a 26.3 ± 0.1 {{abbr|Ma|million years old}} shoshonite, 23 – 16 Ma or probable Pliocene limestone, Cretaceous black shales, late Eocene mudstone and middle to late Eocene sedimentary breccias. There are at least seven seamounts located on the western flank of the ridge with three samples from their flanks dated between 33 and 21.5 Ma.{{sfn|Collot|Sutherland|Etienne|Patriat|2023|loc=2.2 Physiography and Geology of Norfolk Ridge}}{{efn|An earlier report was of 8 seamounts, by some of the same authors, of which 4 had been sampled.{{sfn|Mortimer|Patriat|Gans|Agranier|2020}} Other subsequent publications by the same group map less than 8 seamounts.{{sfn|Gans|Mortimer|Patriat|Turnbull|2023|loc=Figure. 1.}}}} Quaternary coral reefs and intraplate basalts that are much younger at 2–3 Ma are found on Norfolk Island.{{sfn|Collot|Sutherland|Etienne|Patriat|2023|loc=2.2 Physiography and Geology of Norfolk Ridge}}

{{notelist}}

{{reflist|refs={{cite web|url=https://marineregions.org/gazetteer.php?p=details&id=7084|title=Marine Gazetteer: Norfolk Ridge|access-date=23 November 2024}}}}

;Sources

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{{Oceanic features of Zealandia|state=collapsed}}

Category:Zealandia

Category:Underwater ridges of the Pacific Ocean

Category:Geography of the New Zealand seabed

Category:Geology of Zealandia