An Ultraslow-Spreading Class of Ocean Ridge

Total Page:16

File Type:pdf, Size:1020Kb

An Ultraslow-Spreading Class of Ocean Ridge articles An ultraslow-spreading class of ocean ridge Henry J. B. Dick, Jian Lin & Hans Schouten Woods Hole Oceanographic Institution, Woods Hole, Massachusetts 02543, USA ........................................................................................................................................................................................................................... New investigations of the Southwest Indian and Arctic ridges reveal an ultraslow-spreading class of ocean ridge that is characterized by intermittent volcanism and a lack of transform faults. We find that the mantle beneath such ridges is emplaced continuously to the seafloor over large regions. The differences between ultraslow- and slow-spreading ridges are as great as those between slow- and fast-spreading ridges. The ultraslow-spreading ridges usually form at full spreading rates less than about 12 mm yr21, though their characteristics are commonly found at rates up to approximately 20 mm yr21. The ultraslow-spreading ridges consist of linked magmatic and amagmatic accretionary ridge segments. The amagmatic segments are a previously unrecognized class of accretionary plate boundary structure and can assume any orientation, with angles relative to the spreading direction ranging from orthogonal to acute. These amagmatic segments sometimes coexist with magmatic ridge segments for millions of years to form stable plate boundaries, or may displace or be displaced by transforms and magmatic ridge segments as spreading rate, mantle thermal structure and ridge geometry change. Ocean ridges spreading at less than ,20 mm yr21 comprise from fast- to slow-spreading and slow- to ultraslow-spreading ,20,000 km of the ,55,000 km global ridge system1, but until tectonics (Fig. 1b). recently have been little studied. On the basis of studies at faster Magmatic accretionary ridge segments are second-order seg- spreading rates, ocean ridges have been divided into fast-, intermedi- ments that link together between transform faults to make up ate-, and slow-spreading, each with distinctive morphologic charac- first-order segments16. They are considered the basic unit of mag- teristics (Fig. 1a). Slow-spreading ridges (less than ,55 mm yr21) matic accretion, and at slow-spreading ridges often have circular have deep rift valleys with highly variable relief from ,400 to negative mantle Bouguer anomalies (MBAs) centred on them, 2,500 m (ref. 2) and rough rift mountain topography weakly suggesting focused melt and/or mantle flow resulting in thicker correlated to spreading rate3. Fast-spreading ridges (,80– crust at their centres17–20. As there are no transform faults defining a 180 mm yr21) have low (,400 m) axial highs4, sometimes with first-order segmentation at ultraslow rates, we use the term ‘super- small linear depressions (less than ,100 m wide and less than segment’ to describe distinct physiographic regions consisting of ,10 m deep, for example5) at their crests, and minimal rift moun- linked magmatic and amagmatic ridge segments. tain topography uncorrelated to spreading rate. Intermediate- Magmatic segments form sub-perpendicularly to the least prin- spreading ridges (,55–70 mm yr21; ref. 2) have long alternating cipal compressive stress, at an angle intermediate to the ridge trend sections with either slow- or fast-spreading ridge morphology6–8. and orthogonal to the spreading direction, for example21,22. Mor- Slow-spreading ridges near mantle hotspots that have an axial rise phologically, they consist of linear axial highs or troughs with saddle (for example, the Reykjanes ridge), and abrupt changes in mor- points at the segment centres and rift valley walls consisting of phology at intermediate-spreading-rate ridges, show that ridge staircase normal boundary faults. In the absence of transform faults, morphology is not strictly dependent on spreading rate, but may these structures occur in sets overlapping en echelon or connect by reflect variations in ridge geometry, melt supply, and mantle small non-transform discontinuities to accommodate plate bound- composition and thermal structure. ary trends that are oblique to the spreading direction. Where the But this classification also does not take into account variations ridge trend is highly oblique (for example, the Mohns ridge), intra- in crustal thickness with spreading rate. Although seismic crustal rift faults and axial ridges often have sigmoidal traces where they thickness shows little dependency on spreading rate down to merge with rift valley bounding faults that run at higher angles sub- 20 mm yr21, it then drops off rapidly (Fig. 1b). Models for buoyant parallel to the ridge trend21. The close interaction of these two fault and passive plate-driven mantle flow attribute this to conductive sets shows that they are part of an integrated system accommo- cooling from above depressing the top of the mantle melting dating oblique extension during brittle faulting in the shallow crust column and limiting melt production9–12. Thus, changes in ridge (for example, ref. 22). geometry, mantle composition, flow and thermal structure that at Amagmatic accretionary ridge segments are a key component of faster rates would have a minor effect, dramatically affect crustal ultraslow-spreading ridges, replacing transform faults while extend- production and tectonics at very slow spreading rates13,14, creating a ing the zone of lithospheric accretion. In contrast to magmatic class of ridges that is distinct from previous categories. segments, they assume any orientation relative to the spreading Just as the East Pacific Rise is the only fast-spreading ridge, the direction, and are usually marked by an axial trough rarely more only ultraslow-spreading ridge is the Gakkel ridge in the Arctic than a kilometre deep that may extend 50 km or more. They have Ocean: an 1,800-km-long ridge without transform faults spreading only scattered volcanics or a thin basalt carapace, virtually no 8to13mmyr21 (ref.15).Thevery-slow-spreading(14– seismic layer 3 (for example, ref. 23), expose abundant mantle 16 mm yr21) Southwest Indian ridge (SWIR) and the remaining peridotite, and have weak magnetization and a relatively positive Arctic ridge system (13–18 mm yr21) are transitional between slow MBA. The basic accretion unit appears to be mantle horst blocks and ultraslow. Just as intermediate-rate ridges alternate between fast rising up through the rift valley floor along an axis running parallel and slow morphology, these ridges alternately exhibit slow or ultra- to the plate boundary trend. These are subsequently uplifted to slow ridge characteristics over long sections. Thus, there are two create the axial trough walls—often creating single ,148–208 low- intermediate-ridge classes rather than one, representing transitions angle fault surfaces bounding lenticular peridotite ridges. NATURE | VOL 426 | 27 NOVEMBER 2003 | www.nature.com/nature © 2003 Nature Publishing Group 405 articles The SWIR from 98 to 258 E East of Mayes seamount, there is a 180-km-long, 4,200-m-deep 0 0 The SWIR has a very oblique trend—typically ,608 from the oblique amagmatic segment from 118 30 to 148 24 E, oriented 328 spreading direction—and is an example of a transitional ridge from the spreading direction. It has an axial trough with local deep between slow and ultraslow. Long sections are similar to slow- areas to 4,700 m. Twenty-two dredges (2,574 kg) recovered 46.2% spreading ocean ridges (that is, second-order magmatic segments serpentinized peridotites, 2.6% dunite, 14.2% pillow basalt, 19.9% linked by transform faults). Other sections lack transforms and basalt and diabase, and 12.6% hydrothermal silica, sepiolite, and have the character of ultraslow ridges, consisting of sub-orthogonal massive sulphides from the trough walls and floor. As even a thin ,50-km-long magmatic segments linked by amagmatic oblique basalt flow effectively covers peridotite emplaced to the seafloor, the troughs (for example, ref. 24). This slow to ultraslow transitional dredge statistics and lack of gabbro show that igneous crust is thin behaviour is probably largely due to the influence of ridge geometry. or absent here and that the terrain is largely created by faulting. As obliquity increases ridge length, mantle upwelling rate must slow Although the trough floor is rough, with ,500-m relief, there is no proportionately (Fig. 2b, inset). This is expressed by the spreading morphologic evidence of a neovolcanic zone. Rather, long irregular component perpendicular to the ridge trend: the effective spreading axial horst blocks rise up from the valley floor. Dredging, physio- rate for mantle upwelling (ESR). At very slow spreading rates less graphy, weak magnetization, and positive MBA suggest these blocks than ,20 mm yr21, varying ESR (and mantle composition and temperature) creates a region in the spreading-rate spectrum where ridges can assume either a slow-spreading or an ultraslow-spreading morphology. a 1 The two sharply contrasting supersegments along the 1,000 km of the SWIR between the Shaka fracture zone at 98 E and the Prince Rise Edward fracture zone at 258 E, provides a case in point (Fig. 2). The 0 eastern ‘orthogonal’ supersegment, mapped in ref. 25, extends 600 km from 168 to 258 E and has 330- and 191-km-long subsections oriented approximately perpendicularly to the spreading direction Rift –1 linked by a 150-km slightly oblique (,108) section (Fig. 2b). From 178 E, the ridge curves smoothly to the southwest, and thus the ESR steadily decreases to the west. At 168
Recommended publications
  • 51. Breakup and Seafloor Spreading Between the Kerguelen Plateau-Labuan Basin and the Broken Ridge-Diamantina Zone1
    Wise, S. W., Jr., Schlich, R., et al., 1992 Proceedings of the Ocean Drilling Program, Scientific Results, Vol. 120 51. BREAKUP AND SEAFLOOR SPREADING BETWEEN THE KERGUELEN PLATEAU-LABUAN BASIN AND THE BROKEN RIDGE-DIAMANTINA ZONE1 Marc Munschy,2 Jerome Dyment,2 Marie Odile Boulanger,2 Daniel Boulanger,2 Jean Daniel Tissot,2 Roland Schlich,2 Yair Rotstein,2,3 and Millard F. Coffin4 ABSTRACT Using all available geophysical data and an interactive graphic software, we determined the structural scheme of the Australian-Antarctic and South Australian basins between the Kerguelen Plateau and Broken Ridge. Four JOIDES Resolution transit lines between Australia and the Kerguelen Plateau were used to study the detailed pattern of seafloor spreading at the Southeast Indian Ridge and the breakup history between the Kerguelen Plateau and Broken Ridge. The development of rifting between the Kerguelen Plateau-Labuan Basin and the Broken Ridge-Diamantina Zone, and the evolution of the Southeast Indian Ridge can be summarized as follows: 1. From 96 to 46 Ma, slow spreading occurred between Antarctica and Australia; the Kerguelen Plateau, Labuan Basin, and Diamantina Zone stretched at 88-87 Ma and 69-66 Ma. 2. From 46 to 43 Ma, the breakup between the Southern Kerguelen Plateau and the Diamantina Zone propagated westward at a velocity of about 300 km/m.y. The breakup between the Northern Kerguelen Plateau and Broken Ridge occurred between 43.8 and 42.9 Ma. 3. After 43 Ma, volcanic activity developed on the Northern Kerguelen Plateau and at the southern end of the Ninetyeast Ridge. Lava flows obscured the boundaries of the Northern Kerguelen Plateau north of 48°S and of the Ninetyeast Ridge south of 32°S, covering part of the newly created oceanic crust.
    [Show full text]
  • Description of Map Units Northeast Asia Geodynamics Map
    DESCRIPTION OF MAP UNITS NORTHEAST ASIA GEODYNAMICS MAP OVERLAP ASSEMBLAGES (Arranged alphabetically by map symbol) ad Adycha intermountain sedimentary basin (Miocene and Pliocene) (Yakutia) Basin forms a discontinuous chain along the foot of southwestern slope of Chersky Range in the Yana and Adycha Rivers basins. Contain Miocene and Pliocene sandstone, pebble gravel conglomerate, claystone, and minor boulder gravel conglomerate that range up to 400 m thick. REFERENCES: Grinenko and others, 1998. ag Agul (Rybinsk) molasse basin (Middle Devonian to Early Carboniferous) (Eastern Sayan) Consists of Middle Devonian through Early Carboniferous aerial and lacustrine sand-silt-mudstone, conglomerate, marl, and limestone with fauna and flora. Tuff, tuffite, and tuffaceous rock occur in Early Carboniferous sedimentary rocks. Ranges up to 2,000 m thick in southwestern margin of basin. Unconformably overlaps Early Devonian rocks of South Siberian volcanic-plutonic belt and Precambrian and early Paleozoic rocks of the Siberian Platform and surrounding fold belts. REFERENCES: Yanov, 1956; Graizer, Borovskaya, 1964. ags Argun sedimentary basin (Early Paleozoic) (Northeastern China) Occurs east of the Argun River in a discontinuously exposed, northeast-trending belt and consists of Cambrian and Ordovician marine, terrigenous detrital, and carbonate rocks. Cambrian units are composed of of feldspar- quartz sandstone, siltstone, shale and limestone and contain abundant Afaciacyathus sp., Bensocyathus sp., Robustocyathus yavorskii, Archaeocyathus yavorskii(Vologalin), Ethomophyllum hinganense Gu,o and other fossils. Ordovicain units consist of feldspar-quartz sandstone, siltstone, fine-grained sandstone and phylitic siltstone, and interlayered metamorphosed muddy siltstone and fine-grained sandstone with brachiopods, corals, and trilobites. Total thickness ranges up to 4,370 m. Basin unconformably overlies the Argunsky metamorphic terrane.
    [Show full text]
  • Did the 1999 Earthquake Swarm on Gakkel Ridge Open a Volcanic Conduit? a Detailed Teleseismic Data Analysis Carsten Riedel, Vera Schlindwein
    Did the 1999 earthquake swarm on Gakkel Ridge open a volcanic conduit? A detailed teleseismic data analysis Carsten Riedel, Vera Schlindwein To cite this version: Carsten Riedel, Vera Schlindwein. Did the 1999 earthquake swarm on Gakkel Ridge open a volcanic conduit? A detailed teleseismic data analysis. Journal of Seismology, Springer Verlag, 2009, 14 (3), pp.505-522. 10.1007/s10950-009-9179-6. hal-00537995 HAL Id: hal-00537995 https://hal.archives-ouvertes.fr/hal-00537995 Submitted on 20 Nov 2010 HAL is a multi-disciplinary open access L’archive ouverte pluridisciplinaire HAL, est archive for the deposit and dissemination of sci- destinée au dépôt et à la diffusion de documents entific research documents, whether they are pub- scientifiques de niveau recherche, publiés ou non, lished or not. The documents may come from émanant des établissements d’enseignement et de teaching and research institutions in France or recherche français ou étrangers, des laboratoires abroad, or from public or private research centers. publics ou privés. J Seismol (2010) 14:505–522 DOI 10.1007/s10950-009-9179-6 ORIGINAL ARTICLE Did the 1999 earthquake swarm on Gakkel Ridge open a volcanic conduit? A detailed teleseismic data analysis Carsten Riedel · Vera Schlindwein Received: 19 February 2009 / Accepted: 2 November 2009 / Published online: 20 November 2009 © Springer Science + Business Media B.V. 2009 Abstract In 1999, a seismic swarm of 237 tele- ascending toward the potential conduit during the seismically recorded events marked a submarine beginning of April 1999, indicating an opening of eruption along the Arctic Gakkel Ridge, later on the vent.
    [Show full text]
  • Effusive and Explosive Volcanism on the Ultraslow-Spreading Gakkel Ridge, 85E
    Article Volume 13, Number 10 6 October 2012 Q10005, doi:10.1029/2012GC004187 ISSN: 1525-2027 Effusive and explosive volcanism on the ultraslow-spreading Gakkel Ridge, 85E Claire W. Pontbriand MIT-WHOI Joint Program in Oceanography, 266 Woods Hole Road, MS 24, Woods Hole, Massachusetts 02543, USA ([email protected]) S. Adam Soule, Robert A. Sohn, Susan E. Humphris, Clayton Kunz, and Hanumant Singh Woods Hole Oceanographic Institution, 266 Woods Hole Road, MS 24, Woods Hole, Massachusetts 02543, USA ([email protected]; [email protected]; [email protected]; [email protected]; [email protected]) Ko-ichi Nakamura Institute of Geology and Geoinformation, National Institute of Advanced Industrial Science and Technology, 1-1-1 Higashi, Tsukuba 305-8567, Japan ([email protected]) Martin Jakobsson Department of Geological Sciences, Stockholm University, SE-10691 Stockholm, Sweden ([email protected]) Timothy Shank Woods Hole Oceanographic Institution, 266 Woods Hole Road, MS 24, Woods Hole, Massachusetts 02543, USA ([email protected]) [1] We use high-definition seafloor digital imagery and multibeam bathymetric data acquired during the 2007 Arctic Gakkel Vents Expedition (AGAVE) to evaluate the volcanic characteristics of the 85E seg- ment of the ultraslow spreading Gakkel Ridge (9 mm yrÀ1 full rate). Our seafloor imagery reveals that the axial valley is covered by numerous, small-volume (order 1000 m3) lava flows displaying a range of ages and morphologies as well as unconsolidated volcaniclastic deposits with thicknesses up to 10 cm. The valley floor contains two prominent volcanic lineaments made up of axis-parallel ridges and small, cra- tered volcanic cones.
    [Show full text]
  • Quaternary Stratigraphy of the Northwind Ridge, Arctic Ocean
    Quaternary Stratigraphy of the Northwind Ridge, Arctic Ocean THESIS Presented in Partial Fulfillment of the Requirements for the Degree Master of Science in the Graduate School of The Ohio State University By Kevin Allen Crawford B.S. Graduate Program in Geological Sciences The Ohio State University 2010 Master's Examination Committee: Peter-Noel Webb, Advisor Leonid Polyak Lawrence A. Krissek Copyright by Kevin A Crawford 2010 Abstract The Arctic Ocean plays an important role in modulating the world‘s climate. Changes in sea-ice albedo and the export of freshwater into the North Atlantic could have serious repercussions to the climate patterns far beyond the Arctic. To understand fully the impacts of the retreating sea-ice cover and the warming Arctic Ocean we need to look into the past for clues. Paleoenvironments of the Arctic Ocean can be reconstructed by using sea-floor sediment constituents, such as paleobiological and mineral components as well as chemical and paleomagnetic parameters. Three cores raised from the Northwind Ridge, north of the Alaskan continental margin, were chosen to investigate sedimentary patterns and related paleoenvironments in the western Arctic Ocean across a time frame from the Holocene to estimated early Pleistocene. These cores show a range of sedimentation rates decreasing from south to north, thus allowing a development of a relatively high-resolution Upper Quaternary stratigraphy at the southern part of the ridge and a lower-resolution, yet longer stratigraphy for its northern part. In addition to this long stratigraphic coverage, the northern core has well-preserved calcareous microfauna, which provides new insights into paleoceanographic environments.
    [Show full text]
  • Insights on the Indian Ocean Tectonics and Geophysics Supported by GMT Polina Lemenkova
    Insights on the Indian Ocean tectonics and geophysics supported by GMT Polina Lemenkova To cite this version: Polina Lemenkova. Insights on the Indian Ocean tectonics and geophysics supported by GMT. Riscuri si Catastrofe, ”Babes-Bolyai” University from Cluj-Napoca, Faculty of Geography, 2020, 27 (2), pp.67- 83. 10.24193/RCJ2020_12. hal-03033533 HAL Id: hal-03033533 https://hal.archives-ouvertes.fr/hal-03033533 Submitted on 1 Dec 2020 HAL is a multi-disciplinary open access L’archive ouverte pluridisciplinaire HAL, est archive for the deposit and dissemination of sci- destinée au dépôt et à la diffusion de documents entific research documents, whether they are pub- scientifiques de niveau recherche, publiés ou non, lished or not. The documents may come from émanant des établissements d’enseignement et de teaching and research institutions in France or recherche français ou étrangers, des laboratoires abroad, or from public or private research centers. publics ou privés. Distributed under a Creative Commons Attribution| 4.0 International License Riscuri și catastrofe, an XX, vol, 27 nr. 2/2020 INSIGHTS ON THE INDIAN OCEAN TECTONICS AND GEOPHYSICS SUPPORTED BY GMT POLINA LEMENKOVA1 Abstract. Insights on the Indian Ocean Tectonics and Geophysics Supported by GMT. This paper presented analyzed and summarized data on geological and geophysical settings about the tectonics and geological structure of the seafloor of the Indian Ocean by thematic visualization of the topographic, geophysical and geo- logical data. The seafloor topography of the Indian Ocean is very complex which includes underwater hills, isolated mountains, underwater canyons, abyssal and ac- cumulative plains, trenches. Complex geological settings explain seismic activity, repetitive earthquakes, and tsunami.
    [Show full text]
  • Seafloor Hydrothermal Activity Around a Large Non-Transform
    Journal of Marine Science and Engineering Article Seafloor Hydrothermal Activity around a Large Non-Transform Discontinuity along Ultraslow-Spreading Southwest Indian Ridge (48.1–48.7◦ E) Dong Chen 1,2, Chunhui Tao 2,3,*, Yuan Wang 2, Sheng Chen 4, Jin Liang 2, Shili Liao 2 and Teng Ding 1 1 Institute of Marine Geology, College of Oceanography, Hohai University, Nanjing 210098, China; [email protected] (D.C.); [email protected] (T.D.) 2 Key Laboratory of Submarine Geosciences, SOA & Second Institute of Oceanography, MNR, Hangzhou 310012, China; [email protected] (Y.W.); [email protected] (J.L.); [email protected] (S.L.) 3 School of Oceanography, Shanghai Jiao Tong University, Shanghai 200240, China 4 Ocean Technology and Equipment Research Center, School of Mechanical Engineering, Hangzhou Dianzi University, Hangzhou 310018, China; [email protected] * Correspondence: [email protected] Abstract: Non-transform discontinuity (NTD) is one category of tectonic units along slow- and ultraslow-spreading ridges. Some NTD-related hydrothermal fields that may reflect different driving mechanisms have been documented along slow-spreading ridges, but the discrete survey strategy makes it hard to evaluate the incidence of hydrothermal activity. On ultraslow-spreading ridges, fewer NTD-related hydrothermal activities were reported. Factors contributing to the occurrence of hydrothermal activities at NTDs and whether they could be potential targets for hydrothermal explo- Citation: Chen, D.; Tao, C.; Wang, Y.; Chen, S.; Liang, J.; Liao, S.; Ding, T. ration are poorly known. Combining turbidity and oxidation reduction potential (ORP) sensors with Seafloor Hydrothermal Activity a near-bottom camera, Chinese Dayang cruises from 2014 to 2018 have conducted systematic towed around a Large Non-Transform surveys for hydrothermal activity around a large NTD along the ultraslow-spreading Southwest ◦ Discontinuity along Indian Ridge (SWIR, 48.1–48.7 E).
    [Show full text]
  • Geophysical Journal International
    Geophysical Journal International Geophys. J. Int. (2013) doi: 10.1093/gji/ggt372 Geophysical Journal International Advance Access published October 11, 2013 Cretaceous to present kinematics of the Indian, African and Seychelles plates Graeme Eagles∗ and Ha H. Hoang Department of Earth Sciences, Royal Holloway University of London, Egham, Surrey, TW20 0EX, United Kingdom. E-mail: [email protected] Downloaded from Accepted 2013 September 16. Received 2013 September 13; in original form 2012 November 12 SUMMARY An iterative inverse model of seafloor spreading data from the Mascarene and Madagascar http://gji.oxfordjournals.org/ basins and the flanks of the Carlsberg Ridge describes a continuous history of Indian–African Plate divergence since 84 Ma. Visual-fit modelling of conjugate magnetic anomaly data from near the Seychelles platform and Laxmi Ridge documents rapid rotation of a Seychelles Plate about a nearby Euler pole in Palaeocene times. As the Euler pole migrated during this rotation, the Amirante Trench on the western side of the plate accommodated first convergence and later divergence with the African Plate. The unusual present-day morphology of the Amirante GJI Geodynamics and tectonics Trench and neighbouring Amirante Banks can be related to crustal thickening by thrusting and at Alfred Wegener Institut fuer Polar- und Meeresforschung Bibliothek on October 11, 2013 folding during the convergent phase and the subsequent development of a spreading centre with a median valley during the divergent phase. The model fits FZ trends in the north Arabian and east Somali basins, suggesting that they formed in India–Africa Plate divergence. Seafloor fabric in and between the basins shows that they initially hosted a segmented spreading ridge that accommodated slow plate divergence until 71–69 Ma, and that upon arrival of the Deccan–Reunion´ plume and an increase to faster plate divergence rates in the period 69–65 Ma, segments of the ridge lengthened and propagated.
    [Show full text]
  • 21. Tectonic Evolution of the Atlantis Ii Fracture Zone1
    Von Herzen, R.P., Robinson, P.T., et al., 1991 Proceedings of the Ocean Drilling Program, Scientific Results,Vol. 118 21. TECTONIC EVOLUTION OF THE ATLANTIS II FRACTURE ZONE1 Henry J.B. Dick,2 Hans Schouten,2 Peter S. Meyer,2 David G. Gallo,2 Hugh Bergh,3 Robert Tyce,4 Phillipe Patriat,5 Kevin T.M. Johnson,2 Jon Snow,2 and Andrew Fisher6 ABSTRACT SeaBeam echo sounding, seismic reflection, magnetics, and gravity profiles were run along closely spaced tracks (5 km) parallel to the Atlantis II Fracture Zone on the Southwest Indian Ridge, giving 80% bathymetric coverage of a 30- × 170-nmi strip centered over the fracture zone. The southern and northern rift valleys of the ridge were clearly defined and offset north-south by 199 km. The rift valleys are typical of those found elsewhere on the Southwest Indian Ridge, with relief of more than 2200 m and widths from 22 to 38 km. The ridge-transform intersections are marked by deep nodal basins lying on the transform side of the neovolcanic zone that defines the present-day spreading axis. The walls of the transform generally are steep (25°-40°), although locally, they can be more subdued. The deepest point in the transform is 6480 m in the southern nodal basin, and the shallowest is an uplifted wave-cut terrace that exposes plutonic rocks from the deepest layer of the ocean crust at 700 m. The transform valley is bisected by a 1.5-km-high median tectonic ridge that extends from the northern ridge-transform intersection to the midpoint of the active transform.
    [Show full text]
  • CHAPTER 2 Aseismic Ridges of the Northeastern Indian Ocean
    CHAPTER 2 Aseismic ridges of the northeastern Indian Ocean 2.1 Evolution of the Indian Ocean 2.2 Major Aseismic Ridges 2.2.1 The Ninetyeast Ridge 2.2.2 The Chagos-Laccadive Ridge 2.2.3 The 85°E Ridge 2.2.4 The Comorin Ridge 2.2.5 The Broken Ridge 2.3 Other Major Structural Features 2.3.1 The Kerguelen Plateau 2.3.2 The Elan Bank 2.3.3 The Afanasy Nikitin seamount Chapter 2 Aseismic ridges of the northeastern Indian Ocean 2.1 Evolution of the Indian Ocean The initiation of the Indian Ocean commenced with the breakup of the Gondwanaland super-continent into two groups of continental masses during the Mesozoic period (Norton and Sclater, 1979). The first split of the Gondwanaland may possibly have associated with the Karoo mega-plume (Lawver and Gahagan, 1998). Followed by this rifting phase, during the late Jurassic, the Mozambique and Somali basins have formed by seafloor spreading activity of series of east-west trending ridge segments. Thus, the Gondwanaland super-continent divided into western and eastern continental blocks. The Western Gondwanaland consisted of Africa, Arabia and South America, whereas the East Gondwanaland consisted of Antarctica, Australia, New Zeeland, Seychelles, Madagascar and India-Sri Lanka (Figure 2.1). After initial break-up, the East Gondwanaland moved southwards from the West Gondwanaland and led to gradual enlargement of the intervening seaways between them (Bhattacharya and Chaubey, 2001). Both West and East Gondwanaland masses have further sub-divided during the Cretaceous period. Approximate reconstructions of continental masses of the Gondwanaland from Jurassic to Present illustrating the aforesaid rifting events are shown in Figure 2.1 (Royer et al., 1992).
    [Show full text]
  • The Indian Ocean Diverse Ecosystems Harbor Distinctive Deep-Sea Life and Sought-After Minerals
    A fact sheet from April 2018 IFM-GEOMAR The Indian Ocean Diverse ecosystems harbor distinctive deep-sea life and sought-after minerals Overview Vast abyssal plains, mountain chains, and seamounts cover the bottom of the Indian Ocean. Each area is home to life forms suited to its particularities—and each also holds valuable minerals that could be removed through seabed mining. Hydrothermal vents spew superheated, mineral-laden water into their surroundings that, when cooled, forms towers containing copper, cobalt, nickel, zinc, gold, and rare earth elements. These minerals are essential to modern economies. The vent zones are biologically rich as well, supporting mussels, stalked barnacles, scaly-foot snails, and a variety of microbes with potential biomedical and industrial applications. Atop the Indian Ocean’s abyssal plains are more than a billion potato-size nodules with rich concentrations of manganese, copper, cobalt, and nickel. On and near the nodules, wildlife—such as sponges, sea cucumbers, and fish—has evolved to flourish in the deep cold and darkness. Seabed mining is expected to have a significant and long-lasting impact on these deep-sea ecosystems. Mining equipment would remove or degrade habitats, sediment plumes could smother nearby life, and noise and light could harm the unique species that have evolved in order to live here. The International Seabed Authority (ISA) was established by the Law of the Sea treaty to manage seabed mining in areas beyond national jurisdiction while protecting the marine environment. The ISA is drafting regulations to accomplish these objectives with rules on where and how seabed mining could occur.
    [Show full text]
  • 38. Tectonic Constraints on the Hot-Spot Formation of Ninetyeast Ridge1
    Weissel, J., Peirce, J., Taylor, E., Alt, J., et al. 1991 Proceedings of the Ocean Drilling Program, Scientific Results, Vol. 121 38. TECTONIC CONSTRAINTS ON THE HOT-SPOT FORMATION OF NINETYEAST RIDGE1 Jean-Yves Royer,2 John W. Peirce,3 and Jeffrey K. Weissel4 ABSTRACT This paper examines the constraints on the tectonic setting of Ninetyeast Ridge, based on a compilation of bathymetric and magnetic data from the basins surrounding Ninetyeast Ridge in the Indian Ocean that includes the magnetic profiles collected under way during ODP Leg 121. Magnetic data in the Central Indian Basin demonstrate that the spreading center immediately west of Ninetyeast Ridge jumped to the south by a total amount of 11° between 68 and 46 Ma, implying that parts of the mirror image of Ninetyeast Ridge on the Antarctic plate were transferred onto the Indian plate. The obliquity of Ninetyeast Ridge relative to the fracture zone pattern and the occurrence of an Eocene extinct spreading axis in the Wharton Basin suggest that the northern part of Ninetyeast Ridge was emplaced by intraplate volcanism on the Indian plate, whereas the middle and southern parts of the ridge were emplaced along transform plate boundaries. The northward drift of the Indian plate over a single hot spot is the most plausible origin for Ninetyeast Ridge. Based on a recent kinematic model for the relative motions of the Indian, Antarctic, and Australian plates, we present a simple model that reconciles most of the available observations for Ninetyeast Ridge: Paleomagnetism, distribution of basement ages, geochemistry, and geometry. In addition, the model predicts a slow westward migration of the Kerguelen/Ninetyeast hot spot with respect to the Antarctic and Australian plates between the Late Cretaceous and early Oligocene (84 to 36 Ma).
    [Show full text]