Lamont seamount chain is a chain of submarine mountains in the eastern Pacific Ocean which are named "Sasha", "MIB", "MOK", "DTD" and "NEW". They are located close to the East Pacific Rise and reach a minimum depth of 1,629 metres (5,344 ft).

Lamont seamount chain is located in Pacific Ocean
Lamont seamount chain
Lamont seamount chain
Lamont seamount chain (Pacific Ocean)
Location
Coordinates10°00′N 104°30′W / 10.000°N 104.500°W / 10.000; -104.500[1]

These seamounts are submarine volcanoes of Pleistocene to Holocene age that are usually capped off by summit calderas and craters. They have erupted lava flows of tholeiitic composition; the last eruption may have occurred less than 8,000 years ago.

Geography and geomorphology edit

The Lamont seamount chain is a group of five seamounts in the Pacific Ocean;[2] from southeast to northwest they are known as "Sasha",[3] "MIB", "MOK", "DTD" and "NEW"[1] and there is an additional unnamed seamount southwest from "NEW".[4] The seamounts were discovered in 1983 and named later.[5] Brisingid echinoderms have been observed on the seamounts.[6]

The seamounts reach heights of 1–1.4 kilometres (0.62–0.87 mi) and have summit craters/calderas,[2] that on "DTD", "MOK" and "NEW" form nested, complex calderas.[7] Horseshoe-shaped volcanic ridges accompany the calderas and lava effusion appears to have preferentially occurred on the margins of the calderas, along with mass wasting.[8] The Lamont seamount chain forms a 50 kilometres (31 mi) long chain and the individual seamounts surrounded by lava cones 140–100 metres (460–330 ft) high.[2] The shallowest part of the chain is on one of the western seamounts and lies at 1,629 metres (5,344 ft) depth[9] while Sasha reaches to 1,890 metres (6,200 ft), "MIB" to 1,630 metres (5,350 ft) depth, "MOK" to 1,640 metres (5,380 ft) and "NEW" to 1,670 metres (5,480 ft);[10] in general the seamounts shallow westward and their outline changes from conical to more elongated.[5] East of the Lamont seamounts is a nascent volcano.[11]

Geology edit

While the Clipperton Fracture Zone is located just north, the East Pacific Rise lies east of the seamounts;[12] Sasha Seamount lies just 8 kilometres (5.0 mi) from the Rise.[3] It appears to contain a magma chamber at that latitude and seems to have produced voluminous volcanism that generated a topographic elevation that is now associated with the Lamont seamounts.[2] The volcanism is quite young and accompanied by hydrothermal activity; seafloor spreading here proceeds at a rate of 11 centimetres per year (4.3 in/year)[3] and a volcanic eruption in 2003–2006.[13]

The seamounts have produced hyaloclastites,[14] sheet- and lobe-like lava flows as well as pillow lavas[12] and talus. The total volume of each seamount ranges between 140–20 cubic kilometres (33.6–4.8 cu mi)[2] and the volume increases away from the East Pacific Rise, which along with other patterns indicates a progressive development of the seamount as they move away from the East Pacific Rise.[3] They appear to have been formed under the influence both of fracture zones and of a melt anomaly that also formed a 200–400 metres (660–1,310 ft) topographic anomaly west of the Lamont seamount chain[15] along with elongated volcanic structures;[14] a bathymetric swell is also noted around the seamounts[16] as well as a 150 metres (490 ft) deep depression that may be an isostatic moat.[17] Two magma chambers have been identified between Sasha and the EPR.[18] The volcanism may be ultimately the consequence of hotspot activity.[19]

Composition edit

The Lamont seamount chain has erupted tholeiitic magmas[20] which contain olivine and plagioclase phenocrysts[21] as well as spinel but little clinopyroxene.[20] All samples taken from the seamounts contain sulfide globules, including cubanite and pyrrhotite.[22] In some samples, carbonates, celadonite, iron hydroxides, manganese crusts and mica are found.[23] They are relatively primitive magmas that were not stored over long timespans in the crust[24] and undergo simple fractional crystallization processes;[25] their sources appear to be distinct from the magma sources of the East Pacific Rise.[26]

Geochronology edit

The Lamont seamounts probably formed within the last 400,000 years.[15] While the ages of the seamounts are not known, they are by necessity younger than the underlying 740,000 - 100,000 years old seafloor; the lack of sediment cover and thick ferromanganese deposits as well as the youthful appearance of lava flows also speaks for a young age[2] although there is no evidence of hydrothermal activity, past or present.[16] The reflectance of the seafloorm has been used to infer increasing ages from 33,000 years at Sasha to 230,000 at "MOK".[10] Radiocarbon dating of foraminifera encased in lava flows of "NEW" seamount has yielded an age of 18,540 ± 216 radiocarbon years ago, indicating recent activity;[8] additionally, a sample from Sasha seamount may be less than 8,000 years old on the basis of a radium-thorium isotope disequilibrium.[27]

References edit

Sources edit

  • Batiza, Rodey; Sack, Richard O.; Allan, James F. (1 August 1988). "Cr-rich spinels as petrogenetic indicators; MORB-type lavas from the Lamont seamount chain, eastern Pacific" (PDF). American Mineralogist. 73 (7–8): 741–753. ISSN 0003-004X.
  • Fornari, Daniel J.; Perfit, Michael R.; Allan, James F.; Batiza, Rodey; Haymon, Rachel; Barone, Angela; Ryan, William B.F.; Smith, Terri; Simkin, Tom; Luckman, Mary Ann (June 1988). "Geochemical and structural studies of the Lamont seamounts: seamounts as indicators of mantle processes". Earth and Planetary Science Letters. 89 (1): 63–83. doi:10.1016/0012-821X(88)90033-7.
  • Global Volcanism Program (November 2006). Wunderman, R. (ed.). "Report on Northern EPR at 9.8°N (Undersea Features)". Bulletin of the Global Volcanism Network. 31 (11). Smithsonian Institution. doi:10.5479/si.gvp.bgvn200611-334050. ISSN 1050-4818.
  • Lavelle, J. W.; Thurnherr, A. M.; Ledwell, J. R.; McGillicuddy, D. J.; Mullineaux, L. S. (31 December 2010). "Deep ocean circulation and transport where the East Pacific Rise at 9–10°N meets the Lamont seamount chain" (PDF). Journal of Geophysical Research. 115 (C12). doi:10.1029/2010JC006426. hdl:1912/4330.
  • Lundstrom, C. C.; Sampson, D. E.; Perfit, M. R.; Gill, J.; Williams, Q. (10 June 1999). "Insights into mid-ocean ridge basalt petrogenesis: U-series disequilibria from the Siqueiros Transform, Lamont Seamounts, and East Pacific Rise". Journal of Geophysical Research: Solid Earth. 104 (B6): 13043. doi:10.1029/1999JB900081.
  • Marjanović, Milena; Carbotte, Suzanne M.; Stopin, Alexandre; Singh, Satish C.; Plessix, René-Édouard; Marjanović, Miloš; Nedimović, Mladen R.; Canales, Juan Pablo; Carton, Hélène D.; Mutter, John C.; Escartín, Javier (29 September 2023). "Insights into dike nucleation and eruption dynamics from high-resolution seismic imaging of magmatic system at the East Pacific Rise". Science Advances. 9 (39). doi:10.1126/sciadv.adi2698. PMC 10541011.
  • Ryan, William B. F.; Barone, Angela M. (10 July 1990). "Single plume model for asynchronous formation of the Lamont Seamounts and adjacent East Pacific Rise terrains". Journal of Geophysical Research: Solid Earth. 95 (B7): 10801–10827. doi:10.1029/JB095iB07p10801. ISSN 2156-2202.
  • Sack, Richard O.; Fornari, Daniel J.; Perfit, Michael R.; Batiza, Rodey; Allan, James F. (1 October 1989). "Petrology of Lavas from the Lamont Seamount Chain and Adjacent East Pacific Rise, 10° N". Journal of Petrology. 30 (5): 1245–1298. doi:10.1093/petrology/30.5.1245. ISSN 0022-3530.
  • Zhang, Ruiyan; Fau, Marine; Mah, Christopher; Eléaume, Marc; Zhang, Dongsheng; Zhou, Yadong; Lu, Bo; Wang, Chunsheng (February 2024). "Systematics of deep-sea starfish order Brisingida (Echinodermata: Asteroidea), with a revised classification and assessments of morphological characters". Molecular Phylogenetics and Evolution. 191: 107993. doi:10.1016/j.ympev.2023.107993.