Three Kings Ridge
{{short description|Deep sea plateau, north of New Zealand}}
{{Infobox rockunit
| name = Three Kings Ridge
| image = Zealandia, topographic map.jpg
| caption = The Three Kings Ridge (unlabelled) extends northward from the northern tip of the North Island of New Zealand in this map of Zealandia
| type = Igneous
| age = Oligocene-Miocene {{fossil range|37.5|20}}
| period =
| prilithology = Basalt, mantle peridotite, trachybasalt through to rarer andesite
| otherlithology =
| namedfor = Three Kings Islands
| namedby =
| region = South Pacific
| country = New Zealand
| coordinates = {{coord|-31.05|172.85|type:landmark_globe:earth_region:NZ|display=ti}}
| unitof =
| subunits =
| underlies =
| overlies =
| thickness =
| extent =
| area =
| map =
| map_caption =
}}
The Three Kings Ridge, sometimes known as Three Kings Rise and more rarely at its southern end as the Three Kings Bank is a deep sea westward facing volcanic arc of Zealandia continental crust extending from {{convert|55|km|mi}} northwest of Cape Reinga / Te Rerenga Wairua, New Zealand on a line bisecting New Caledonia and Fiji in the South Pacific Ocean. Its southern portion contains the Manawatāwhi / Three Kings Islands which have biological significance as they are host to unique species and important marine ecosystems.{{cite journal|last=Judd |first=Warren |date=1996 |title=The clifftop world of the Three Kings |url= https://www.nzgeo.com/stories/the-clifftop-world-of-the-three-kings/ |journal=New Zealand Geographic |issue=29 |access-date=28 February 2023}}
Geology
The ridge along with its northern continuation, the Loyalty Ridge that extends north of New Caledonia, is now a relatively well studied, greater than {{convert|3000|km|abbr=on}} long feature of Zealandia tectonics.{{cite journal|title=Detailed 40Ar/39Ar Geochronology of the Loyalty and Three Kings Ridges Clarifies the Extent and Sequential Development of Eocene to Miocene Southwest Pacific Remnant Volcanic Arcs |first1=P. B. |last1=Gans|first2= N. |last2=Mortimer|first3= M. |last3=Patriat|first4= R. E. |last4=Turnbull|first5= M. P. |last5=Crundwell|first6= A. |last6=Agranier|first7= A. T. |last7=Calvert|first8= G. |last8=Seward|first9= S. |last9=Etienne|first10= P. M. J. |last10=Durance|first11= H. J. |last11=Campbell|first12= J. |last12=Collot|year= 2023 |doi=10.1029/2022GC010670|journal=Geochemistry, Geophysics, Geosystems|volume=24|issue=2|bibcode=2023GGG....2410670G |s2cid=255041563 |doi-access=free}} It is a relatively rigid portion of continental crust compared to the oceanic crust in surrounding basins about {{convert|25|km|abbr=on}} in thickness.{{cite journal|last1=Herzer|first1= R|last2=Barker|first2= D|last3=Roest |first3= W|last4=Mortimer |first4= N|year=2011 |title=Oligocene-Miocene spreading history of the northern South Fiji Basin and implications for the evolution of the New Zealand plate boundary|volume= 12|doi= 10.1029/2010GC003291|journal=Geochemistry, Geophysics, Geosystems |issue= 2|bibcode= 2011GGG....12.2004H|s2cid= 56089661|doi-access= free}} While regarded as inactive there have been moderate sized earthquakes at the northern end of the ridge.[https://earthquake.usgs.gov/earthquakes/eventpage/us6000jrtp/map?historic-seismicity=true&shakemap-intensity=false USGS Regional Information:Seismotectonics of the Eastern Margin of the Australia Plate] It can be regarded as a stranded western remnant arc segment split off by intra-arc and cross-arc rifting during back-arc basin opening from the still active eastern arc segments close to the Pacific trench and slab. The {{convert|400|km|abbr=on}} long{{cite journal|first1=Arnaud |last1=Agranier|first2= Martin |last2=Patriat|first3= Nick |last3=Mortimer |first4= Julien |last4=Collot |first5= Samuel |last5=Etienne |first6= Patricia |last6=Durance|first7= Phil |last7=Gans |title=Oligo-Miocene subduction-related volcanism of the Loyalty and Three Kings ridges, SW Pacific: a precursor to the Tonga-Kermadec arc |journal=Lithos |volume= 436–437 |year=2023 |page=106981 |issn=0024-4937 |doi=10.1016/j.lithos.2022.106981 |bibcode=2023Litho.43606981A |s2cid=254306179 |doi-access=free }} Cook Fracture Zone that is aligned with the two ridges separates it from the Loyalty Ridge and is associated with about {{convert|250|km|abbr=on}} lateral displacement at the southern end of the central Minerva-Cook spreading zone of the South Fiji Basin. In the middle of the area between the two ridges is the youngest dated volcanics, being the DR22A seamount at 19.7 ± 0.5 Ma. The northern deep tip of the ridge has mudstone at {{convert| 3700|m|abbr=on}} water depth that is stratigraphically dated to 20.9 to 18.7 Ma. To its east is the Norfolk basin separating it from the Norfolk Ridge in the Tasman Sea. To its west is the South Fiji Basin with its former spreading sea floor of the Cook Fracture Zone. To its south a trough extends from the Norfolk Basin separating it from the volcanic alignment of the Norfolk Ridge with the northern North Island. It has been postulated that the Three Kings Ridge has been subsequently separated by the now inactive Vening Meinesz Fault Zone from the Miocene volcanic arcs of Northland in the North Island, and its extension under the Tasman Sea of the Northland Plateau.{{cite journal|last1=Mortimer|first1= N.|last2= Herzer|first2= R. H.|last3= Gans |first3= P. B.|last4= Laporte-Magoni |first4= C.|last5= Calvert |first5= A. T.|last6=Bosch |first6= D. |year=2007 |title= Oligocene–Miocene tectonic evolution of the South Fiji Basin and Northland Plateau, SW Pacific Ocean: Evidence from petrology and dating of dredged rocks |journal= Marine Geology |volume= 237 |issue=1–2 |pages= 1–24 |doi=10.1016/j.margeo.2006.10.033|bibcode= 2007MGeol.237....1M}} However, there is a distinct age difference between the 25 million years ago dates of the southern part of the ridge eruptives and the nearest North Island volcanics.
The seabed on the rise has a component from a large drowned Oligocene island of metamorphic rocks, mantle peridotite, and Gondwana derived continental rocks dating from 38 million years ago{{cite journal|title=Arc-continent collision forming a large island between New Caledonia and New Zealand in the Oligocene|first1=Sebastien |last1=Meffre|first2= Anthony J. |last2=Crawford |first3=Patrick G. |last3=Quilty |journal=ASEG Extended Abstracts |volume=1|pages= 1–3|year=2006|doi=10.1071/ASEG2006ab111|s2cid=130355847 }} (the oldest basement is dated 37.5 Ma). These 39–36 million year old Eocene lavas are now known to be subordinate to later activity and are mainly confined to the western side of the ridge. However a 32 million year old andesitic centre has been characterised at the northeastern area of the ridge. There was a pulse of voluminous late Oligocene to early Miocene (25 to 22 million years ago) volcanic activity within the Cook Fracture Zone and the northern portions of the ridge that now dominate. The ridge surface is mainly trachybasalt and basaltic andesite, with some trachyandesite, and andesite, but no rhyolite volcanics. Its sides are basalt suggesting these are basement as they are also found in the nearly basins. Sporadic volcanic activity after this is evidenced by say samples of andesite from 20 million years ago. The ridge has been mainly below sealevel since 21 million years ago due to Australian and Pacific Plate extension but the present islands to the ridges south were still connected to each other, but not New Zealand, at the sea level minimum of 7000 years ago.{{Cite web| title = Estuary origins |url=https://niwa.co.nz/te-kuwaha/tools-and-resources/ng%C4%81-waihotanga-iho-the-estuary-monitoring-toolkit-for-iwi/estuary-origins | publisher = National Institute of Water and Atmospheric Research| access-date = 1 March 2023}}
=Tectonic implications=
It has been postulated that the relatively rigid Three Kings Ridge had a role in the emplacement of the Northland Allochthon and this may contain rocks inherited from a Three Kings arc collision. This collision as the continental crust of the ridge moved southeast about 25.5–22 million years ago would have been had to have been associated with a subduction flip in the postulated model.
File:Princes Islands New Zealand Aotearoa.jpg are the southeastern manifestation of the Three Kings Ridge.]]
Islands, reefs and seamounts
{{main|Manawatāwhi / Three Kings Islands}}
The ridge has to its south a group of 13 presently uninhabited islands where the South Pacific Ocean and Tasman Sea meet. These are separated from the New Zealand North Island by a {{convert|8|km|abbr=on}} wide submarine trough that is at least {{convert|200|m|abbr=on}} deep and may be associated with the Vening Meinesz Fault Zone.
=Bio-genetic separation=
There is genetic drift evidence in insect and snail populations that these islands have been connected together but separate from the North Island from the point of view of individual species for up to 24 million years, but as recently as 2.24 million years with others.{{cite journal|first1=Thomas R. |last1=Buckley |first2= Richard A. B. |last2=Leschen |title= Comparative phylogenetic analysis reveals long-term isolation of lineages on the Three Kings Islands, New Zealand |journal=Biological Journal of the Linnean Society |volume=108 |issue=2 |year= 2013|pages =361–377|doi=10.1111/j.1095-8312.2012.02009.x|s2cid=83698404 |doi-access=free }} In the case of the islands flax snail Placostylus bollonsi Suter, they are more strongly related to a New Caledonia species, that any New Zealand species.{{cite journal|first1=Ponder |last1=WF |last2= Colgan |first2=DJ |last3=Gleeson |first3=DM | last4=Sherley |first4=GH |year=2003 |title=Relationships of Placostylus from Lord Howe Island: an investigation using the mitochondrial cytochrome c oxidase 1 gene| journal=Molluscan Research |volume=23 |issue=2 |pages=159–178| doi= 10.1071/MR03001|url=https://www.researchgate.net/publication/238084592 |doi-access=free }}
See also
- {{annotated link|Lord Howe Rise}}
- {{annotated link|Chatham Rise}}
- {{annotated link|Norfolk Ridge}}
- {{annotated link|South Tasman Rise}}
References
{{reflist}}
{{Oceanic features of Zealandia|state=collapsed}}
Category:Underwater ridges of the Pacific Ocean
Category:Volcanism of Zealandia
Category:Volcanoes of the New Zealand outlying islands
Category:Volcanoes of Zealandia