The Ninety East Ridge (also rendered as Ninetyeast Ridge, 90E Ridge or 90°E Ridge) is a mid-ocean ridge on the Indian Ocean floor named for its near-parallel strike along the 90th meridian at the center of the Eastern Hemisphere. It is approximately 5,000 kilometres (3,100 mi) in length and can be traced topographically from the Bay of Bengal southward towards the Southeast Indian Ridge (SEIR), though the feature continues to the north where it is hidden beneath the sediments of the Bengal Fan. The ridge extends between latitudes 31°S and 9°N and has an average width of 200 km.[1]
The Ninety East Ridge at the centre of the picture and the Chagos-Laccadive Ridge on the upper left side
The ridge divides the Indian Ocean into the West and East Indian Ocean. The northeastern side is named the Wharton Basin and ceases at the western end of the Diamantina Fracture Zone which passes to the east and almost to the Australian continent.[2]
The ridge is primarily composed of Ocean Island Tholeiites (OIT), a subset of basalt which were shown to increase in age from approximately 43.2 ± 0.5 million years ago in the south to 81.8 ± 2.6 million years ago in the north.[3] A more recent analysis using modern Ar–Ar techniques gives an age progression from 77 million years ago at 5°N to 43 million years ago at 31°S.[4] Even more recent work with more samples gives a range of 82 to 37 million years ago[5]: 1178 This age progression has led geologists to theorize that a hotspot in the mantle beneath the Indo-Australian Plate created the ridge as the plate has moved northward in the late Mesozoic and Cenozoic. This theory was supported by analysis of the chemistry of the Kerguelen Plateau and Rajmahal Traps, which were believed to represent the flood basalts erupted at the initiation of volcanism at the Kerguelen hotspot which was then sheared in two as the Indian subcontinent moved northward.[3] However the area of the Ninety East Ridge as well as being related to the hotspot was noted to be part of the diffuse boundary between the Indian Plate and Australian Plate.[6]: 411–12 This has led to modifications of understanding. Some maintain close to the original view.[7]: 1105–6 The Ninety East Ridge has no systematic isotopic variation observed along the ridge and this is inconsistent with the hypothesis of an ageing mantle plume origin for all of the ridge.[5]: 1177 At least three distinct sources must have contributed to the basalts of the ridge.[5]: 1177 This results in the interpretation that at least two separate hotspots contributed and the Ninety East Ridge is predominantly a historic divergent plate boundary with eruptives from a deep mantle source.[5]: 1177 [7][8]: 131
Surveyingedit
The ridge has been surveyed several times in the past, including several times by the Deep Sea Drilling Program (DSDP). In 2007, the RV Roger Revelle collected bathymetric, magnetic and seismic data together with dredge samples from nine sites along the ridge as part of an Integrated Ocean Drilling Program (IODP) site survey intended to examine the hotspot hypothesis for the ridge.[9]
Originsedit
It had been assumed that India and Australia were on a single tectonic plate for at least the last 32 million years. However, considering the high level of large earthquakes in the Ninety East Ridge area and the evidence of deformation in the central Indian Ocean, it is more appropriate to consider the deformed region in the central Indian Ocean as a broad plate boundary zone separating the Indian Plate and the Australian Plate.[1][10]
Paleontologyedit
During the late Paleocene around 60 million years ago, parts of the Ninety East Ridge were temporarily exposed for 2–3 million years as volcanic islands probably 1,000 km from the nearest land. Preserved pollen and plant cuticle fragments have been found in boreholes drilled on the ridge. The flora has been noted to be most similar to Australian and Antarctic floras, rather than to Indian floras, including Podocarpaceae conifers, as well as 15 species of angiosperms, including members of Arecaceae, Chloranthaceaesensu lato,Lauraceae, Gunnera, Gillbeea, and possibly Callitrichaceae.[11]
^ abStein, S.; Okal, W. A. (1974). "Seismicity and Tectonics of the Ninetyeast Ridge Area: Evidence for Internal Deformation of the Indian Plate" (PDF). Journal of Geophysical Research. 83 (B5): 2233. Bibcode:1978JGR....83.2233S. doi:10.1029/jb083ib05p02233. Retrieved 23 May 2015.
^Stow, D. A. V. (2006) Oceans : an illustrated reference Chicago : University of Chicago Press, ISBN0-226-77664-6 - page 127 for map of Indian Ocean and ridges
^ abWeis, D.; et al. (1993). "The Influence of Mantle Plumes in Generation of Indian Oceanic Crust". Synthesis of Results from Scientific Drilling in the Indian Ocean. Geophysical Monograph Series. Vol. 70. pp. 57–89. Bibcode:1992GMS....70...57W. doi:10.1029/gm070p0057. ISBN9781118668030.
^Frey, F.A.; Pringle, M.; Meleney, P.; Huang, S.; Piotrowski, A. (March 2011). "Diverse mantle sources for Ninetyeast Ridge magmatism: Geochemical constraints from basaltic glasses". Earth and Planetary Science Letters. 303 (3–4): 215–224. Bibcode:2011E&PSL.303..215F. doi:10.1016/j.epsl.2010.12.051.
^ abcdNobre Silva, IG; Weis, D; Scoates, JS; Barling, J (2013). "The Ninetyeast Ridge and its relation to the Kerguelen, Amsterdam and St. Paul hotspots in the Indian Ocean". Journal of Petrology. 54 (6): 1177–210. doi:10.1093/petrology/egt009.
^Gaina, C; Müller, RD; Brown, BJ; Ishihara, T (2003). "Microcontinent formation around Australia". In Hillis, RR; Müller, RD (eds.). Evolution and Dynamics of the Australian Plate(PDF). Geological Society of Australia Special Publication 22 and Geological Society of America Special Paper 372. pp. 405–16. Retrieved 2023-11-14.
^ abSreejith, KM; Krishna, KS (28 February 2015). "Magma production rate along the Ninetyeast Ridge and its relationship to Indian plate motion and Kerguelen hot spot activity". Geophysical Research Letters. 42 (4): 1105–12. doi:10.1002/2014GL062993.
^Bredow, E; Steinberger, B (16 January 2018). "Variable melt production rate of the Kerguelen hotspot due to long‐term plume‐ridge interaction". Geophysical Research Letters. 45 (1): 126–36. doi:10.1002/2017GL075822. hdl:10852/70913.
^. The University of Texas at Austin. Archived from the original on 2017-05-10. Retrieved 2016-07-07.
^Van Orman, J.; Cochran, J. R.; Weissel, J. K.; Jestin, F. (1995). "Distribution of shortening between the Indian and Australian plates in the central Indian Ocean". Earth and Planetary Science Letters. 133 (1–2): 35–46. Bibcode:1995E&PSL.133...35V. CiteSeerX10.1.1.508.956. doi:10.1016/0012-821x(95)00061-g.
^Carpenter, Raymond J.; Truswell, Elizabeth M.; Harris, Wayne K. (2010-03-02). "Lauraceae fossils from a volcanic Palaeocene oceanic island, Ninetyeast Ridge, Indian Ocean: ancient long-distance dispersal?: Indian Ocean Lauraceae fossils". Journal of Biogeography. 37 (7): 1202–1213. doi:10.1111/j.1365-2699.2010.02279.x. S2CID 83060879.
Further readingedit
Sager, William W. (2007). (PDF). Scripps Institution of Oceanography. Archived from the original (PDF) on 2016-03-04. Retrieved 2011-09-23.
Nobre Silva, I. G. (2011). Deciphering mantle source components in basalts from hotspot tracks and oceanic islands (Thesis). University of British Columbia. doi:10.14288/1.0053092.
Sager, W. W.; Paul, C.F.; Krishna, K.S.; Pringle, M.S.; Eisin, A.E.; Frey, F.A.; Rao, D.G.; Levchenko, O.V. (September 2010). "Large fault fabric of the Ninetyeast Ridge implies near-spreading ridge formation" (PDF). Geophysical Research Letters. 37 (L17304): n/a. Bibcode:2010GeoRL..3717304S. doi:10.1029/2010GL044347.
Verzhbitsky, E. V. (2003). "Geothermal regime and genesis of the Ninety-East and Chagos-Laccadive ridges". Journal of Geodynamics. 35 (3): 289–302. Bibcode:2003JGeo...35..289V. doi:10.1016/S0264-3707(02)00068-6.
ninety, east, ridge, also, rendered, ninetyeast, ridge, ridge, ridge, ocean, ridge, indian, ocean, floor, named, near, parallel, strike, along, 90th, meridian, center, eastern, hemisphere, approximately, kilometres, length, traced, topographically, from, benga. The Ninety East Ridge also rendered as Ninetyeast Ridge 90E Ridge or 90 E Ridge is a mid ocean ridge on the Indian Ocean floor named for its near parallel strike along the 90th meridian at the center of the Eastern Hemisphere It is approximately 5 000 kilometres 3 100 mi in length and can be traced topographically from the Bay of Bengal southward towards the Southeast Indian Ridge SEIR though the feature continues to the north where it is hidden beneath the sediments of the Bengal Fan The ridge extends between latitudes 31 S and 9 N and has an average width of 200 km 1 The Ninety East Ridge at the centre of the picture and the Chagos Laccadive Ridge on the upper left side Contents 1 Description 1 1 Surveying 2 Origins 3 Paleontology 4 See also 5 References 6 Further reading 7 External links 7 1 90 East Ridge Formation 94 Ma present Description editThe ridge divides the Indian Ocean into the West and East Indian Ocean The northeastern side is named the Wharton Basin and ceases at the western end of the Diamantina Fracture Zone which passes to the east and almost to the Australian continent 2 The ridge is primarily composed of Ocean Island Tholeiites OIT a subset of basalt which were shown to increase in age from approximately 43 2 0 5 million years ago in the south to 81 8 2 6 million years ago in the north 3 A more recent analysis using modern Ar Ar techniques gives an age progression from 77 million years ago at 5 N to 43 million years ago at 31 S 4 Even more recent work with more samples gives a range of 82 to 37 million years ago 5 1178 This age progression has led geologists to theorize that a hotspot in the mantle beneath the Indo Australian Plate created the ridge as the plate has moved northward in the late Mesozoic and Cenozoic This theory was supported by analysis of the chemistry of the Kerguelen Plateau and Rajmahal Traps which were believed to represent the flood basalts erupted at the initiation of volcanism at the Kerguelen hotspot which was then sheared in two as the Indian subcontinent moved northward 3 However the area of the Ninety East Ridge as well as being related to the hotspot was noted to be part of the diffuse boundary between the Indian Plate and Australian Plate 6 411 12 This has led to modifications of understanding Some maintain close to the original view 7 1105 6 The Ninety East Ridge has no systematic isotopic variation observed along the ridge and this is inconsistent with the hypothesis of an ageing mantle plume origin for all of the ridge 5 1177 At least three distinct sources must have contributed to the basalts of the ridge 5 1177 This results in the interpretation that at least two separate hotspots contributed and the Ninety East Ridge is predominantly a historic divergent plate boundary with eruptives from a deep mantle source 5 1177 7 8 131 Surveying edit The ridge has been surveyed several times in the past including several times by the Deep Sea Drilling Program DSDP In 2007 the RV Roger Revelle collected bathymetric magnetic and seismic data together with dredge samples from nine sites along the ridge as part of an Integrated Ocean Drilling Program IODP site survey intended to examine the hotspot hypothesis for the ridge 9 Origins editIt had been assumed that India and Australia were on a single tectonic plate for at least the last 32 million years However considering the high level of large earthquakes in the Ninety East Ridge area and the evidence of deformation in the central Indian Ocean it is more appropriate to consider the deformed region in the central Indian Ocean as a broad plate boundary zone separating the Indian Plate and the Australian Plate 1 10 Paleontology editDuring the late Paleocene around 60 million years ago parts of the Ninety East Ridge were temporarily exposed for 2 3 million years as volcanic islands probably 1 000 km from the nearest land Preserved pollen and plant cuticle fragments have been found in boreholes drilled on the ridge The flora has been noted to be most similar to Australian and Antarctic floras rather than to Indian floras including Podocarpaceae conifers as well as 15 species of angiosperms including members of Arecaceae Chloranthaceae sensu lato Lauraceae Gunnera Gillbeea and possibly Callitrichaceae 11 See also editEighty Five East RidgeReferences edit a b Stein S Okal W A 1974 Seismicity and Tectonics of the Ninetyeast Ridge Area Evidence for Internal Deformation of the Indian Plate PDF Journal of Geophysical Research 83 B5 2233 Bibcode 1978JGR 83 2233S doi 10 1029 jb083ib05p02233 Retrieved 23 May 2015 Stow D A V 2006 Oceans an illustrated reference Chicago University of Chicago Press ISBN 0 226 77664 6 page 127 for map of Indian Ocean and ridges a b Weis D et al 1993 The Influence of Mantle Plumes in Generation of Indian Oceanic Crust Synthesis of Results from Scientific Drilling in the Indian Ocean Geophysical Monograph Series Vol 70 pp 57 89 Bibcode 1992GMS 70 57W doi 10 1029 gm070p0057 ISBN 9781118668030 Frey F A Pringle M Meleney P Huang S Piotrowski A March 2011 Diverse mantle sources for Ninetyeast Ridge magmatism Geochemical constraints from basaltic glasses Earth and Planetary Science Letters 303 3 4 215 224 Bibcode 2011E amp PSL 303 215F doi 10 1016 j epsl 2010 12 051 a b c d Nobre Silva IG Weis D Scoates JS Barling J 2013 The Ninetyeast Ridge and its relation to the Kerguelen Amsterdam and St Paul hotspots in the Indian Ocean Journal of Petrology 54 6 1177 210 doi 10 1093 petrology egt009 Gaina C Muller RD Brown BJ Ishihara T 2003 Microcontinent formation around Australia In Hillis RR Muller RD eds Evolution and Dynamics of the Australian Plate PDF Geological Society of Australia Special Publication 22 and Geological Society of America Special Paper 372 pp 405 16 Retrieved 2023 11 14 a b Sreejith KM Krishna KS 28 February 2015 Magma production rate along the Ninetyeast Ridge and its relationship to Indian plate motion and Kerguelen hot spot activity Geophysical Research Letters 42 4 1105 12 doi 10 1002 2014GL062993 Bredow E Steinberger B 16 January 2018 Variable melt production rate of the Kerguelen hotspot due to long term plume ridge interaction Geophysical Research Letters 45 1 126 36 doi 10 1002 2017GL075822 hdl 10852 70913 Seismic Project Information KNOX06RR Ninetyeast Ridge IODP Survey The University of Texas at Austin Archived from the original on 2017 05 10 Retrieved 2016 07 07 Van Orman J Cochran J R Weissel J K Jestin F 1995 Distribution of shortening between the Indian and Australian plates in the central Indian Ocean Earth and Planetary Science Letters 133 1 2 35 46 Bibcode 1995E amp PSL 133 35V CiteSeerX 10 1 1 508 956 doi 10 1016 0012 821x 95 00061 g Carpenter Raymond J Truswell Elizabeth M Harris Wayne K 2010 03 02 Lauraceae fossils from a volcanic Palaeocene oceanic island Ninetyeast Ridge Indian Ocean ancient long distance dispersal Indian Ocean Lauraceae fossils Journal of Biogeography 37 7 1202 1213 doi 10 1111 j 1365 2699 2010 02279 x S2CID 83060879 Further reading editSager William W 2007 Cruise Report KNOX06RR R V Roger Revelle 18 June to 6 August 2007 Phuket to Singapore PDF Scripps Institution of Oceanography Archived from the original PDF on 2016 03 04 Retrieved 2011 09 23 Nobre Silva I G 2011 Deciphering mantle source components in basalts from hotspot tracks and oceanic islands Thesis University of British Columbia doi 10 14288 1 0053092 Sager W W Paul C F Krishna K S Pringle M S Eisin A E Frey F A Rao D G Levchenko O V September 2010 Large fault fabric of the Ninetyeast Ridge implies near spreading ridge formation PDF Geophysical Research Letters 37 L17304 n a Bibcode 2010GeoRL 3717304S doi 10 1029 2010GL044347 Verzhbitsky E V 2003 Geothermal regime and genesis of the Ninety East and Chagos Laccadive ridges Journal of Geodynamics 35 3 289 302 Bibcode 2003JGeo 35 289V doi 10 1016 S0264 3707 02 00068 6 External links edit90 East Ridge Formation 94 Ma present edit Video including 90 East Ridge Formation 94 Ma million years ago present YouTube Plate tectonics Paleogeography amp Ice Ages dual hemispheres by Christopher Scotese 2019 Field Museum of Natural History amp Northwestern University Video including 90 East Ridge Formation 94 Ma million years ago present YouTube Plate Tectonics 540Ma Modern World by Christopher Scotese 2016 Field Museum of Natural History amp Northwestern University 3 S 90 E 3 S 90 E 3 90 Retrieved from https en wikipedia org w index php title Ninety East Ridge amp oldid 1215384103, wikipedia, wiki, book, books, library,
