The South Fiji Basin ( also Fiji Basin[5] ) is a large 4 to 4.7 km (2.5 to 2.9 mi) deep[3] oceanic basin in the south-west Pacific Ocean, south of Fiji. It was formed from the then Indo-Australian Plate and is delimited to the north west by the New Hebrides Trench, and the Hunter Fracture Zone, to the west by the Three Kings Ridge, to the east by the Lau-Colville Ridge, and to the south by the continental shelf of Zealandia.
| South Fiji Basin | |
|---|---|
| Stratigraphic range: | |
The South Fiji Basin is surrounded to the north and east by more geologically active Pacific Ocean seafloor features. The Zealandia continental margin is shown in black. | |
| Type | Igneous |
| Area | 800,000 km2 (310,000 sq mi)[3] |
| Lithology | |
| Primary | mafic basalts |
| Other | Sediments including ashy biogenic sediments[4] |
| Location | |
| Coordinates | 26°00′S 176°00′W / 26.0°S 176.0°W[5] |
| Region | South Pacific |
| Country | Fiji |
| Type section | |
| Named for | Fiji |
Geology
editOver the basement volcanics is deposited up to 500 m (1,600 ft) of sediment.[6] The thicker sediments of the Kupe Abyssal Plain nearer New Zealand and land commenced to accumulate from the end of the Oligocene onwards and terminated in the Pliocene with likely minor contributions from southern Lau-Colville Ridge volcanoes.[7] The oldest basalt dredged from the Minerva Abyssal Plain is 26.0 ± 1.0 Ma but it is unknown if this is of basement or later volcanic origin.[8] However drill site 285 in the Minerva Abyssal Plain also has basement volcanics that are dated to 26 Ma.[8] The oldest other drill basement may be 31 Ma, but this has been questioned without the sample being re-examined.[8] Basalts from the South Fiji Basin are little influenced by subduction, although they can have slight enrichment from a slab component,[9] but come from variably enriched mantle, resulting from mixing between enriched mantle, like FOZO and depleted mantle, like depleted MORB mantle (DMM).[10]
To the north is the Minerva Abyssal Plain which has north west limits of the New Hebrides Trench and the Hunter Fracture Zone.[11] Within this abyssal plain are several seamounts including to the north of the Cook Fracture Zone, Alison Seamount and Coquille Seamount beyond the end of the Three Kings Ridge.[11] Beyond the Fantail Terrace to the north east of the Three Kings Ridge are a number of seamounts that separate the Minerva Abyssal Plain from the southern Kupe Abyssal Plain,[11] in a Central Ridge structure with little overlying sediment.[12] These include Julia, Marion, Matahourua and Mascarin seamounts.[11] To the north east the Minerva Abyssal Plain is bounded by the Lau Terrace rather than the Lau Ridge to the east of the terrace.[11] The Kupe Abyssal Plain is delimited to its west by the Three Kings Ridge and this western portion contains multiple seamounts including the Sarah group, Margot and Devonport group of seamounts.[11] These tend to give younger dates and there is increasing evidence that the Kupe Abyssal Plain is Miocene in age.[13] The seafloor magnetic anomalies of the southern Kupe Abyssal Plain, unlike those further north, have been resolved and indicate NW–SE spreading.[14]
Seamount Geology
editBasalt from Julia Seamount was dated at 22.1±1.8 Ma and Alison at 19.3±1.5 Ma.[8] Matahourua, Mascarin, Marion, Coquille and one Margot seamount dedged sample are ocean island basalts.[15] Marion trachybasalt was dated at 16.2 ± 0.2 Ma and Matahourua basalt at 15 ± 2 Ma.[8] These younger ages must be after spreading had ceased.[1] The Devonport East and Central, Sarah North, Central and West, and one sample from Margot, are trachybasalts or trachyandesite consistent with back arc volcanism and are aged from 19.9 to 21 million years ago.[16][8]
Seismology
editThe basin itself is inactive. However its eastern portions in the present Australian Plate are over the deeply subducted Pacific Plate slab, so many deep ( more than 400 km (250 mi)) and large (more than Mw 6) earthquakes have occurred in historic times.[17] Other earthquake activity is confined to the northwestern margins of the basin.
Tectonics
editThe South Fiji Basin started forming in the Oligocene.[18] The historic interpretation based on magnetic anomaly patterns was that spreading involved a triple junction in the Minerva Abyssal Plain and some disagreement if the Kupe Plain Abyssal spreading was a westward or eastward trend.[6] This means that a full tectonic model consensus can not be reached. However the current best fit model is one of west-dipping Tonga–Kermadec–Hikurangi subduction zone rolling back clockwise, and an approximately east-dipping New Caledonia–Northland subduction zone that rolls back anticlockwise until about 21 million years ago.[19] A maximum half spreading rate of about 5 cm/year (2.0 in/year) has been calculated.[20] The Minerva spreading centres persisted into the Miocene and with the 23 Ma age of a basalt from the Cook Fracture Zone and other samples have been interpreted to have been active after this.[20] The New Hebrides Trench has consumed a large area of crust of the South Fiji Basin since the late Miocene.[7] It is possible that Pacific Plate subduction was followed by Early to Middle Miocene back-arc spreading in the southern South Fiji Basin with a pre-Miocene tectonic configuration that would have resembled the present Lau Basin and Havre Trough.[21] The former Kupe microplate is now fixed to the Australian Plate. Presently the north western South Fiji Basin is probably not being subducted under the New Hebrides Plate at the New Hebrides Trench but rather the margin is a zone of transformation.
Ecology
editThe basin seawater has a temperature of about 2 °C (36 °F) at 4 kilometres (2.5 mi) depth. Fish species known include those from the genus Pachycara (e.g. Pachycara moelleri), large Synaphobranchid, Halosaurs (Aldrovandia affinis) , cusk-eels (Bassogigas spp.. Bassozetus spp., Barathrites iris), and members of the Zoarcidae family.[22] High-energy macrourids are absent at the limited sites sampled.[22] Amongst crustaceans, amphipods including members of the family Lysianassidae, prawns of the genus Benthesicymus (Benthesicymus crenatus, Benthesicymus howensis) and Aristeidae (Cerataspis monstrosus) are found.[23]
See also
editReferences
edit- ^ a b Todd et al. 2011, Section:2.1.3. South Fiji Basin
- ^ Mortimer et al. 2007, Sections:Abstract, Conclusions
- ^ a b Packham & Terrill 1975, p617
- ^ Packham, Gordon H; Andrews, James E. (1975). "26. RESULTS OF LEG 30 AND THE GEOLOGIC HISTORY OF THE SOUTHWEST PACIFIC ARC AND MARGINAL SEA COMPLEX" (PDF). deepseadrilling.org. Retrieved 3 July 2023.
- ^ a b Marine Gazetteer:South Fiji Basin
- ^ a b Mortimer et al. 2007, Section:2.1. South Fiji Basin
- ^ a b Packham & Terrill 1975, p630
- ^ a b c d e f Mortimer et al. 2007, Table 2
- ^ Todd et al. 2011, section:5.2. Havre Ambient Mantle Wedge (AMW)
- ^ Todd et al. 2011, section:Abstract
- ^ a b c d e f Mortimer et al. 2007, Fig.1
- ^ Packham & Terrill 1975, p628
- ^ Herzer et al. 2000, p703
- ^ Herzer et al. 2000, p707
- ^ Mortimer et al. 2007, Section:5.2.1. Less porphyritic (ocean island) basalts
- ^ Mortimer et al. 2007, Section:5.2.2. More porphyritic (potassic) lavas
- ^ "Seismotectonics of the Eastern Margin of the Australia Plate" (PDF). Retrieved 3 July 2023.
- ^ Timm et al. 2019, Section:Introduction
- ^ Schellart, WP; Spakman, W (1 August 2012). "Mantle constraints on the plate tectonic evolution of the Tonga–Kermadec–Hikurangi subduction zone and the South Fiji Basin region". Australian Journal of Earth Sciences. 59 (6): 933–52. Bibcode:2012AuJES..59..933S. doi:10.1080/08120099.2012.679692. S2CID 128890799.
- ^ a b Mortimer et al. 2007, Section:7.5. Hotspot migration trails and basin opening rates
- ^ Herzer et al. 2000, p708
- ^ a b Linley, T; Stewart, AL; McMillan, PJ; Clark, MR; Gerringer, ME; Drazen, JC; Fujii, T; Jamieson, AJ (2017). "Bait attending fishes of the abyssal zone and hadal boundary: Community structure, functional groups and species distribution in the Kermadec, New Hebrides and Mariana trenches". Deep Sea Research Part I: Oceanographic Research Papers. 121: 38–53. Bibcode:2017DSRI..121...38L. doi:10.1016/j.dsr.2016.12.009. ISSN 0967-0637.
- ^ Swan, Ja; Jamieson, AJ; Linley, TD; Yancey, PH (4 February 2021). "Worldwide distribution and depth limits of decapod crustaceans (Penaeoidea, Oplophoroidea) across the abyssal-hadal transition zone of eleven subduction trenches and five additional deep-sea features". Journal of Crustacean Biology. 41 (1). doi:10.1093/jcbiol/ruaa102.
- Sources
- Packham, GH; Terrill, A (1975). "20 Submarine geology of the South Fiji basin. Initial Reports of the Deep Sea Drilling Project" (PDF). deepseadrilling.org. pp. 617–45. Retrieved 3 July 2023.
- Todd, E.; Gill, J. B.; Wysoczanski, R. J.; Hergt, Janet; Wright, I. C.; Leybourne, I.; Mortimer, N. (2011). "Hf isotopic evidence for small‐scale heterogeneity in the mode of mantle wedge enrichment: Southern Havre Trough and South Fiji Basin back arcs". Geochemistry, Geophysics, Geosystems. 12 (9). Bibcode:2011GGG....12.9011T. doi:10.1029/2011GC003683. S2CID 135271738.
- Herzer, R; Mascle, J; Davy, B; Ruellan, E; Mortimer, N; Laporte, C; Duxfield, A (30 May 2000). "New constraints on the New Zealand–South Fiji Basin continent-back-arc margin". Comptes Rendus de l'Académie des Sciences, Série IIA. 330 (10): 701–8. Bibcode:2000CRASE.330..701H. doi:10.1016/S1251-8050(00)00185-3.
- Mortimer, N; Herzer, RH; Gans, PB; Laporte-Magoni, C; Calvert, AT; Bosch, D (9 February 2007). "Oligocene–Miocene tectonic evolution of the South Fiji Basin and Northland Plateau, SW Pacific Ocean: Evidence from petrology and dating of dredged rocks" (PDF). Marine Geology. 237 (1–2): 1–24. Bibcode:2007MGeol.237....1M. doi:10.1016/j.margeo.2006.10.033.
- Timm, C.; de Ronde, C. E. J.; Hoernle, K.; Cousens, B.; Wartho, J. A.; Tontini, F. Caratori; Wysoczanski, R.; Hauff, F.; Handler, M. (2019). "New Age and Geochemical Data from the Southern Colville and Kermadec Ridges, SW Pacific: Insights into the recent geological history and petrogenesis of the Proto-Kermadec (Vitiaz) Arc" (PDF). Gondwana Research. 72: 169–193. Bibcode:2019GondR..72..169T. doi:10.1016/j.gr.2019.02.008. S2CID 135048102.