// Workers AI · dad joke modeWhy did Crough Seamount go to therapy? It had a rough sea-son.
Crough Seamount (named after the geologist Thomas Crough[1]) is a seamount in the Pacific Ocean, within the exclusive economic zone of Pitcairn.[2] It rises to a depth of 650 metres (2,130 ft) and is paired with a taller but overall smaller seamount to the east. This seamount has a flat top and probably formed an island in the past. It is about 7-8 million years old, although a large earthquake recorded at its position in 1955 may indicate a recent eruption.
The seamount appears to be part of a long geological lineament with the neighbouring Henderson and Ducie islands, as well as the southern Tuamotus and Line Islands. Such a lineament may have been generated by a hotspot; the nearby Easter hotspot is a candidate hotspot.
Geology and geomorphology
[edit]Regional
[edit]The region lies between and around the islands of Pitcairn and Easter Island.[3] There, the East Pacific Rise is interrupted by a trapezoid microplate known as the Easter Microplate[4] about 400 kilometres (250 mi) wide. Seafloor spreading occurs at a rate of about 16 centimetres per year (6.3 in/year).[3]
There is a topographic swell that connects the two islands and continues eastward towards Sala y Gomez. The origin of this swell and the various volcanoes and seamounts associated with it has been variously explained as either being due to a mantle plume which forms volcanoes that are then carried away through plate motion or by a "hot line" where a number of simultaneously active volcanic centres develop.[3] This geological lineament may extend all the way to Tonga.[5]
Crough seamount was probably formed by the Easter hotspot that also generated Easter Island[6] albeit with the participation of a nearby fracture zone[7] that modified the trend of the hotspot path.[8] In this case the Easter Island-Sala y Gomez ridge and the Crough Seamount would be conjugate volcanic ridges paired across the East Pacific Rise.[9] although it is possible that two separate hotspots were active on the eastern and western side of the East Pacific Rise.[10][11] Another theory postulates that Crough was formed by its own hotspot, the Crough hotspot.[12]
Together with Ducie and Henderson Crough forms a 1,300 kilometres (810 mi) long westward trending lineament[13] with each volcano becoming older the farther west it lies,[14] and which may be a prolongation of the southern Tuamotus[15] which were generated by the same hotspot.[9] Even farther west the hotspot track may include Oeno, Minerve Reef, Marutea, Acton, Rangiroa, the Line Islands and the Mid-Pacific Mountains, although a continuation through the Line Islands is problematic if it is assumed that the Easter hotspot generated this track.[12][16] A different theory has Crough seamount as its own hotspot, that formed the seamounts and islands together with another hotspot ("Larson"),[17] and lesser contributions of the Society and Marquesas hotspot.[18] East of Crough, a series of even younger volcanic ridges continues until the East Pacific Rise[19] where the hotspot may be located.[12] The Crough hotspot may be a conjugate of the Easter hotspot,[20] and sourced from the middle mantle.[17]
Local
[edit]Crough is an east–west trending seamount[4] which rises over 2 kilometres (1.2 mi) from the seafloor to a depth of less than 722 metres (2,369 ft)[21] at 650 metres (2,130 ft).[22] It has a flat top and the presence of coral sands indicates that Crough once emerged above sea level before subsiding to its present depth,[21] having formerly hosted corals[23] and pteropods. Wave erosion that took place when Crough emerged above sea level truncated the seamount, turning it into a flat guyot.[24] Pillow lavas crop out between 1,400–950 metres (4,590–3,120 ft).[25] Crough Seamount has a volume of 660 cubic kilometres (160 cu mi), comparable to that of other submarine volcanoes such as Macdonald seamount, Mehetia and Moua Pihaa.[22]
A second seamount lies nearby and partly overlaps with Crough,[26] it is named Thomas Seamount[27] in honour of a geophysicist.[28] This seamount is even shallower than Crough as it reaches a depth of 600 metres (2,000 ft) but has a smaller volume of 600 cubic kilometres (140 cu mi).[22] Both seamounts are situated at the ends of volcanic ridges.[29]
Composition
[edit]Dredging has yielded both vesicular and porphyritic basalt. Phenocrysts identified include clinopyroxene, olivine and plagioclase. Carbonates and hyaloclastites have also been found, and some samples were covered with manganese crusts[30] and palagonite.[31] Hydrothermal iron crusts have also been found.[25] There are some similarities between the Crough magmas and Easter Island magmas.[32]
Eruption history
[edit]Argon-argon dating has yielded ages of 8.4 to 7.6 million years ago for samples dredged from Crough,[33] while other geological indicators suggest an age of between 7 and 10 million years ago.[34] Other estimates of its age are 4[14]-3 million years.[35]
In 1955, a strong earthquake was recorded on the northern flank of Crough Seamount;[36] the characteristics of the earthquake resemble these of volcanic processes and it is thus possible that Crough Seamount is still active. Such activity may constitute a post-shield stage of volcanism.[35] The earthquake has also been interpreted as a normal fault earthquake[1] which sometimes occur in young oceanic crust, but the 1955 Crough event was considerably stronger than other earthquakes of this type.[37]
References
[edit]- ↑ Irving, Robert.; Dawson, Terence P. (2012). The marine environment of the Pitcairn Islands. Dundee: The Pew Environment Group. ISBN 9781845861612. OCLC 896746178.
- 1 2 3 Hekinian et al. 1995, p. 376.
- 1 2 Hekinian et al. 1995, p. 377.
- ↑ Spencer 1989, p. 6.
- ↑ Hekinian et al. 1995, p. 389.
- ↑ Spencer 1989, p. 5.
- ↑ Searle, Francheteau & Cornaglia 1995, p. 397.
- 1 2 Searle, Francheteau & Cornaglia 1995, p. 417.
- ↑ O'Connor, Stoffers & McWilliams 1995, p. 208.
- ↑ Morgan & Morgan 2007, p. 51.
- 1 2 3 Morgan & Morgan 2007, p. 71.
- ↑ Binard et al. 1996, p. 24.
- 1 2 Bramwell, David; Caujapé-Castells, Juli (2011-07-21). The Biology of Island Floras. Cambridge University Press. p. 241. ISBN 9781139497800.
- ↑ Vacher & Quinn 1997, p. 410.
- ↑ Fletcher, Michael; Wyman, Derek A.; Zahirovic, Sabin (1 July 2020). "Mantle plumes, triple junctions and transforms: A reinterpretation of Pacific Cretaceous – Tertiary LIPs and the Laramide connection". Geoscience Frontiers. 11 (4): 1141. Bibcode:2020GeoFr..11.1133F. doi:10.1016/j.gsf.2019.09.003.
- 1 2 Pockalny et al. 2021, p. 1361.
- ↑ Pockalny et al. 2021, p. 1360.
- ↑ Binard et al. 1996, p. 34.
- ↑ Fletcher, Michael; Wyman, Derek A.; Zahirovic, Sabin (26 September 2019). "Mantle plumes, triple junctions and transforms: A reinterpretation of Pacific Cretaceous – Tertiary LIPs and the Laramide connection". Geoscience Frontiers. 11 (4): 9. Bibcode:2020GeoFr..11.1133F. doi:10.1016/j.gsf.2019.09.003. ISSN 1674-9871.
- 1 2 Hekinian et al. 1995, p. 380.
- 1 2 3 Binard et al. 1996, p. 27.
- ↑ Vacher & Quinn 1997, p. 407.
- ↑ Binard et al. 1996, p. 31.
- 1 2 Stoffers, P.; Glasby, G. P.; Stuben, D.; Renner, R. M.; Pierre, T. G.; Webb, J.; Cardile, C. M. (1993). "Comparative mineralogy and geochemistry of hydrothermal iron-rich crusts from the Pitcairn, Teahitia-mehetia, and Macdonald hot spot areas of the S. W. Pacific". Marine Georesources & Geotechnology. 11 (1): 47. Bibcode:1993MGG....11...45S. doi:10.1080/10641199309379905.
- ↑ Spencer 1989, p. 3.
- ↑ Binard et al. 1996, p. 26.
- ↑ Searle, Francheteau & Cornaglia 1995, p. 400.
- ↑ O’Connor, Regelous & Haase 2024, p. 3.
- ↑ Hekinian et al. 1995, p. 379.
- ↑ Hekinian et al. 1995, p. 382.
- ↑ O’Connor, Regelous & Haase 2024, p. 5.
- ↑ O'Connor, Stoffers & McWilliams 1995, pp. 206–207.
- ↑ Binard et al. 1996, p. 25.
- 1 2 Talandier & Okal 1987, p. 946.
- ↑ Talandier & Okal 1987, p. 945.
Sources
[edit]- Binard, N.; Stoffers, P.; Hékinian, R.; Searle, R.C. (October 1996). "Intraplate en echelon volcanic ridges in the South Pacific west of the Easter microplate". Tectonophysics. 263 (1–4): 23–37. Bibcode:1996Tectp.263...23B. doi:10.1016/S0040-1951(96)00036-4. ISSN 0040-1951.
- Hekinian, Roger; Stoffers, Peter; Akermand, Dietrich; Binard, Nicolas; Francheteau, Jean; Devey, Colin; Garbe-Schönberg, Dieter (August 1995). "Magmatic evolution of the Easter microplate-Crough Seamount region (South East Pacific)". Marine Geophysical Researches. 17 (4): 375–397. Bibcode:1995MarGR..17..375H. doi:10.1007/bf01227041. ISSN 0025-3235. S2CID 129757272.
- Morgan, W. Jason; Morgan, Jason Phipps (2007). "Plate velocities in hotspot reference frame: electronic supplement" (PDF). geosociety.org. doi:10.1130/2007090.
- O'Connor, John M.; Stoffers, Peter; McWilliams, Michael O. (December 1995). "Time-space mapping of Easter Chain volcanism". Earth and Planetary Science Letters. 136 (3–4): 197–212. Bibcode:1995E&PSL.136..197O. CiteSeerX 10.1.1.572.1182. doi:10.1016/0012-821X(95)00176-D. ISSN 0012-821X.
- O’Connor, J.M.; Regelous, M.; Haase, K.M. (2024). "Synchronous motion of the Easter mantle plume and the East Pacific Rise". Nat Commun. 15 (9953). doi:10.1038/s41467-024-54115-2. PMC 11570642.
- Okal, Emile A.; Cazenave, Anny (January 1985). "A model for the plate tectonic evolution of the east-central Pacific based on SEASAT investigations". Earth and Planetary Science Letters. 72 (1): 99–116. Bibcode:1985E&PSL..72...99O. doi:10.1016/0012-821X(85)90120-7. ISSN 0012-821X.
- Pockalny, Robert; Barth, Ginger; Eakins, Barry; Kelley, Katherine A.; Wertman, Christina (1 November 2021). "Multiple melt source origin of the Line Islands (Pacific Ocean)" (PDF). Geology. 49 (11): 1358–1362. Bibcode:2021Geo....49.1358P. doi:10.1130/G49306.1.
- Searle, R.C.; Francheteau, J.; Cornaglia, B. (April 1995). "New observations on mid-plate volcanism and the tectonic history of the Pacific plate, Tahiti to Easter microplate". Earth and Planetary Science Letters. 131 (3–4): 395–421. Bibcode:1995E&PSL.131..395S. doi:10.1016/0012-821X(95)00018-8. ISSN 0012-821X.
- Spencer, T. (1989). "Tectonic and environmental histories in the Pitcairn Group, Palaeogene to present: reconstructions and speculations". Atoll Research Bulletin. 322: 1–22. doi:10.5479/si.00775630.322.1. hdl:10088/5906.
- Talandier, Jacques; Okal, Emile A. (1987). "Seismic detection of underwater volcanism: The example of French Polynesia". Pure and Applied Geophysics. 125 (6): 919–950. Bibcode:1987PApGe.125..919T. doi:10.1007/bf00879361. ISSN 0033-4553. S2CID 128415828.
- Vacher, Leonard H. L.; Quinn, Terrence M. (1997-12-19). Geology and hydrogeology of carbonate islands. Elsevier. ISBN 9780080532479.
25°00′S 121°12′W / 25°S 121.2°W[1]
- 1 2 Spencer 1989, p. 3.