DOCSLIB.ORG

How and When Plume Zonation Appeared During the 132&Thinsp

Total Page：16

File Type：pdf, Size：1020Kb

Download full-text PDF Read full-text
How and When Plume Zonation Appeared During the 132&Thinsp ARTICLE Received 10 Oct 2014 | Accepted 10 Jun 2015 | Published 27 Jul 2015 DOI: 10.1038/ncomms8799 OPEN How and when plume zonation appeared during the 132 Myr evolution of the Tristan Hotspot Kaj Hoernle1,2, Joana Rohde1, Folkmar Hauff1, Dieter Garbe-Scho¨nberg2, Stephan Homrighausen1, Reinhard Werner1 & Jason P. Morgan3 Increasingly, spatial geochemical zonation, present as geographically distinct, subparallel trends, is observed along hotspot tracks, such as Hawaii and the Galapagos. The origin of this zonation is currently unclear. Recently zonation was found along the last B70 Myr of the Tristan-Gough hotspot track. Here we present new Sr–Nd–Pb–Hf isotope data from the older parts of this hotspot track (Walvis Ridge and Rio Grande Rise) and re-evaluate published data from the Etendeka and Parana flood basalts erupted at the initiation of the hotspot track. We show that only the enriched Gough, but not the less-enriched Tristan, component is present in the earlier (70–132 Ma) history of the hotspot. Here we present a model that can explain the temporal evolution and origin of plume zonation for both the Tristan-Gough and Hawaiian hotspots, two end member types of zoned plumes, through processes taking place in the plume sources at the base of the lower mantle. 1 GEOMAR Helmholtz Centre for Ocean Research Kiel, Wischhofstrasse 1-3, 24148 Kiel, Germany. 2 CAU Kiel University, Institute of Geosciences, Ludewig- Meyn-Strasse 10, D-24118 Kiel, Germany. 3 Royal Holloway, University of London, Department of Earth Sciences, Egham Hill, Egham TW20 0EX, UK. Correspondence and requests for materials should be addressed to K.H. (email: [email protected]). NATURE COMMUNICATIONS | 6:7799 | DOI: 10.1038/ncomms8799 | www.nature.com/naturecommunications 1 & 2015 Macmillan Publishers Limited. All rights reserved. ARTICLE NATURE COMMUNICATIONS | DOI: 10.1038/ncomms8799 lthough it has been proposed that some plumes have formation of the South Atlantic Ocean basin23. As the Atlantic had constant compositions through time, such as the opened, ALouisville1 and Kerguelen2,3, spatial geochemical zonation the ridge-centred plume tail formed the Walvis Ridge on the has been found in a variety of hotspot tracks in the Pacific Ocean. African Plate and the Rio Grande Rise (possibly underlain by a These include the Galapagos4–7, Hawaiian8,9, Samoan10, thinned continental block) on the South American Plate. As the Marquesan10,11 and Society12 hotspot tracks, which are believed South Atlantic mid-ocean ridge drifted westwards away from the to be located at the border of the large, lower mantle, low plume tail B50–60 Ma, the hotspot became intraplate forming shear-wave velocity province (LLSVP) beneath the southern the Guyot Province, consisting of separate volcanic tracks leading Pacific9,10,12,13. The longevity of plume zonation is variable for to the active volcanic islands of Tristan da Cunha and Gough24. the different Pacific hotspots. It can be traced for 15–20 Myr Recently published Sr–Nd–Hf–Pb isotope data of samples from along the Galapagos hotspot track6,7, for B4 Myr along the the Tristan-Gough hotspot track reveal that bilateral chemical Society hotspot track12,14, for B5.5 Myr along the Marquesas11,15 zonation can be traced from the Tristan da Cunha and Gough and for up to 2 Myr along the Samoan Islands10,14,16. island groups along the Tristan and Gough subtracks for the last The coexistence of the geochemically distinct Loa and Kea B70 Myr to the southwestern (SW) end of the Walvis Ridge13 trends of the Hawaiian mantle plume has been traced for the last (Fig. 1). The enriched Gough domain exhibits higher 207Pb/204Pb 5 Myr along the island chain9. Little evidence exists for the for a given 206Pb/204Pb and extends to lower 143Nd/144Nd and presence of the Loa component in the Hawaiian seamounts, 176Hf/177Hf ratios and generally higher 87Sr/86Sr ratios compared located west of the Hawaiian Islands and only the Kea component with the more depleted (less enriched) Tristan domain. The has been recognized so far in the Emperor Seamounts and domains form distinct fields on the uranogenic Pb isotope diagram older accreted Hawaiian complexes in Kamchatka17. To address (Fig. 2a). Published geochemical data are, however, insufficient to questions concerning the longevity of plume zonation and how it establish chemical zonation beyond 70 Ma. originates, we investigate the entire history of the Tristan-Gough Here we present new Sr–Nd–Hf–Pb double spike (DS) isotope hotspot here and compare it with what is known about the data from additional samples from the Guyot Province (obtained history of the Hawaiian hotspot. during R/V Akademik Kurchatov, AII-93 Atlantis II, ANT-XXIII/ The Tristan-Gough hotspot track (Fig. 1) represents the classic 5 Polarstern, VM29 Vema, 51 S.A. Agulhas and SO233 Sonne evolution of a hotspot18 with active volcanic islands at its young cruises) and Deep Sea Drilling Programme (DSDP) Sites 525A, end and flood basalt provinces at its older end. It has been termed 527 and 528 at the SW end of the Walvis Ridge to test whether one of the seven hotspots most likely to be derived from the this part of the hotspot track is indeed zoned. More importantly lowermost mantle from a ‘primary’ plume19 with its base we present new data from dredge (VM29 Vema, CIRCE Argo, currently located at the margin of the African LLSVP20,21. The AII–93 Atlantis II, CH19 Jean Charcot, WALDAA–002 Jean emplacement of a Tristan-Gough plume head at the base of the Charcot, RC11 Robert D. Conrad and SO233 Sonne cruises) and Gondwana lithosphere caused massive volcanism forming the DSDP Leg 72 drill samples from the older part of the hotspot Parana (eastern South America) and Etendeka (western Africa) track (central and northeast Walvis Ridge and Rio Grande Rise) flood basalts at B132 Ma22 and may have contributed to determine whether the zonation can be traced further back in to the breakup of Africa from South America and the time, that is, going northeast along the hotspot track. Finally, we ge d 15°S e i R g is d i lv a Etendeka R W c CFBs i Paraná CFBs t n 132 Ma 108–114 Ma a k l c 132 Ma t a A r - t Rio Grande Rise k d n 20°S i ta c s a M ri r T t h g u o G Guyot Province 107 Ma – 87 25°S Site 527 Site 528 Site 525A Site 516F 58–67 Ma 71–72 Ma 30°S 80–87 Ma 47 Ma 49 Ma 36 Ma 33 Ma 35°S Walvis Ridge 46 Ma 27 Ma Rio Grande Rise Tristan da Cunha Islands Guyot Province (Gough track) 37 Ma 27 Ma Gough Island DSDP site 525A Guyot Province (Tristan track) Gough Island 40°S Tristan da Cunha Islands DSDP sites 527 and 528 40°W 35°W 30°W 25°W 15°W 10°W 5°W0° 5°E 10°E Figure 1 | Bathymetric map of the South Atlantic Ocean and its margins showing the Tristan-Gough hotspot track. The map shows the Tristan-Gough hotspot track including the B132 Myr (ref. 22) old Etendeka and Parana continental flood basalt provinces, the Rio Grand Rise and Walvis Ridge (both within the age range B60–115 Ma), the Guyot Province at the southwestern end of the Walvis Ridge containing the Tristan da Cunha and Gough Island groups (B0–60 Ma)24. Ages for late-stage volcanism are not shown. Age range in italics (87–107 Ma) is estimated using a spatial age progression equation24. Sample locations are denoted by symbols: large symbols this study and small symbols as reported in ref. 13. Source of base map is http:// www.geomapapp.org. All sites are from the Deep Sea Drilling Project. The scale bar in the lower right hand corner indicates a distance of B500 km. 2 NATURE COMMUNICATIONS | 6:7799 | DOI: 10.1038/ncomms8799 | www.nature.com/naturecommunications & 2015 Macmillan Publishers Limited. All rights reserved. NATURE COMMUNICATIONS | DOI: 10.1038/ncomms8799 ARTICLE 15.68 and Hawaiian plumes and evaluate the origin of geochemical Gough track Tristan track Gough Island Tristan Islands zonation in both plumes. 15.64 DSDP 525A 527 and 528 Walvis Ridge Results 15.60 Rio Grande Rise 80% 90% Isotopic composition of Tristan-Gough hotspot track lavas. Pb 204 15.56 The new Sr–Nd–Hf–Pb isotope data are presented in (Table 1). Average Pb/ ingrowth corr. We report details about the samples, the major and trace element 207 15.52 data and isotope data with errors in Methods and Supplementary Dataset 1. The Sr–Nd–Hf–Pb isotope data of the new samples 15.48 80% from the Guyot Province and DSDP Sites 525A, 527 and 528 at Atlantic N-MORB 15.44 90% the SW end of the Walvis Ridge confirm the spatial geochemical zonation of the r70 Ma hotspot track proposed by (ref.13; Fig. 2a). The data from the older (470 Ma) hotspot track, central 39.6 and northeast portion of the Walvis Ridge and the Rio Grande 24 39.2 Rise , plot exclusively within the Gough field. They also 80% completely cover the range of the r70 Ma Gough track, Pb 38.8 90% 204 showing that there is no systematic temporal change in the Gough source through time. The Rio Grande Rise samples and Pb/ 38.4 208 some samples from the Walvis Ridge are isotopically as enriched 38.0 as DSDP Site 525A: the enriched mantle one (EMI) end member 80% Atlantic N-MORB 25,26 90% in the South Atlantic .
Load more

Recommended publications
  • C"""- Signature of Author, Joint Program in Oceanography Massachusetts Institute of Technology/ Woods Hole Oceanographic Institution
    GLOBAL ISOTOPIC SIGNATURES OF OCEANIC ISLAND BASALTS by LYNN A. OSCHMANN A.B. BRYN MAWR COLLEGE (1989) SUBMITTED IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF MASTER OF SCIENCE IN OCEANOGRAPHY at the MASSACHUSETTS INSTITUTE OF TECHNOLOGY and the WOODS HOLE OCEANOGRAPHIC INSTITUTION August 1991 @Lynn A. Oschmann 1991 The author hereby grants to MIT, WHOI, and the U.S. Government permission to reproduce and distribute copies of this thesis in whole or in part. %/7_ ) C"""- Signature of Author, Joint Program in Oceanography Massachusetts Institute of Technology/ Woods Hole Oceanographic Institution Certified by - 1% Dr. Stanley R. Hart Senior Scientist, Woods Hole Oceanographic Institution Thesis Supervisor Accepted by Dr. G. Pat Lohman Chairman, Joint Committee for Geology and Geophysics, Massachusetts Institute of Technology/ Woods Hole Oceanographic Institution MVIr 2 GLOBAL ISOTOPIC SIGNATURES OF OCEANIC ISLAND BASALTS by LYNN A. OSCHMANN Submitted to the Department of Earth, Atmospheric and Planetary Sciences Massachusetts Institute of Technology and the Department of Geology and Geophysics Woods Hole Oceanographic Institution August 9, 1991 in partial fulfillment of the requirements for the degree of MASTER OF SCIENCE IN OCEANOGRAPHY ABSTRACT Sr, Nd and Pb isotopic analyses of 477 samples representing 30 islands or island groups, 3 seamounts or seamount chains, 2 oceanic ridges and 1 oceanic plateau [for a total of 36 geographic features] are compiled to form a comprehensive oceanic island basalt [OIB] data set. These samples are supplemented by 90 selected mid-ocean ridge basalt [MORB] samples to give adequate representation to MORB as an oceanic basalt end-member. This comprehensive data set is used to infer information about the Earth's mantle.
    [Show full text]
  • Vulnerable Marine Ecosystems – Processes and Practices in the High Seas Vulnerable Marine Ecosystems Processes and Practices in the High Seas
    ISSN 2070-7010 FAO 595 FISHERIES AND AQUACULTURE TECHNICAL PAPER 595 Vulnerable marine ecosystems – Processes and practices in the high seas Vulnerable marine ecosystems Processes and practices in the high seas This publication, Vulnerable Marine Ecosystems: processes and practices in the high seas, provides regional fisheries management bodies, States, and other interested parties with a summary of existing regional measures to protect vulnerable marine ecosystems from significant adverse impacts caused by deep-sea fisheries using bottom contact gears in the high seas. This publication compiles and summarizes information on the processes and practices of the regional fishery management bodies, with mandates to manage deep-sea fisheries in the high seas, to protect vulnerable marine ecosystems. ISBN 978-92-5-109340-5 ISSN 2070-7010 FAO 9 789251 093405 I5952E/2/03.17 Cover photo credits: Photo descriptions clockwise from top-left: Acanthagorgia spp., Paragorgia arborea, Vase sponges (images courtesy of Fisheries and Oceans, Canada); and Callogorgia spp. (image courtesy of Kirsty Kemp, the Zoological Society of London). FAO FISHERIES AND Vulnerable marine ecosystems AQUACULTURE TECHNICAL Processes and practices in the high seas PAPER 595 Edited by Anthony Thompson FAO Consultant Rome, Italy Jessica Sanders Fisheries Officer FAO Fisheries and Aquaculture Department Rome, Italy Merete Tandstad Fisheries Resources Officer FAO Fisheries and Aquaculture Department Rome, Italy Fabio Carocci Fishery Information Assistant FAO Fisheries and Aquaculture Department Rome, Italy and Jessica Fuller FAO Consultant Rome, Italy FOOD AND AGRICULTURE ORGANIZATION OF THE UNITED NATIONS Rome, 2016 The designations employed and the presentation of material in this information product do not imply the expression of any opinion whatsoever on the part of the Food and Agriculture Organization of the United Nations (FAO) concerning the legal or development status of any country, territory, city or area or of its authorities, or concerning the delimitation of its frontiers or boundaries.
    [Show full text]
  • 20. a Seismic Reflection Study of the Rio Grande Rise1
    20. A SEISMIC REFLECTION STUDY OF THE RIO GRANDE RISE1 Peter F. Barker, Department of Geological Sciences, Birmingham University, Birmingham B15 2TT, England Richard T. Buffler,2 Galveston Marine Geophysics Laboratory, University of Texas at Austin, Galveston, Texas and Luiz A. Gamboa,3 Lamont-Doherty Geological Observatory, Palisades, New York ABSTRACT Seismic reflection profiles have been interpreted in combination with deep-sea drilling data to examine the sedimen- tary evolution of the Rio Grande Rise. Restricted and unevenly distributed seismic reflection coverage (particularly multichannel) and limited well control confined most of our interest to the northern flank of the main western elevated block of the Rise, near to DSDP Site 516. The basement of much of the Rise above approximately 3000 m present depth has the "dipping reflector" character of some continental margins, produced by interbedded lavas and sediments formed directly above sea level. The overlying Late Cretaceous and early Tertiary sediments are mainly pelagic, but lap onto originally subaerial base- ment in places. A major middle Eocene tectonic event (involving uplift, tilting, faulting, and probably local volcanism) resulted in subaerial erosion, submarine slumping, and turbidite deposition. Submarine slides associated with the early stages of this tectonism probably caused the chaotic midsection reflector sequence identified with the middle Eocene Unit 4 at Site 516. Middle Eocene tectonism also produced the central graben of the Rise, which contains rotated fault blocks, and the broad guyot between the graben and Site 516. The guyot shows thick sequences dipping away from the graben and truncated, presumably by subaerial erosion. Prograded biogenic debris, swept off the top by bottom cur- rents after resubmergence in the Oligocene, extended the guyot's top farther.
    [Show full text]
  • Large Igneous Provinces: a Driver of Global Environmental and Biotic Changes, Geophysical Monograph 255, First Edition
    2 Radiometric Constraints on the Timing, Tempo, and Effects of Large Igneous Province Emplacement Jennifer Kasbohm1, Blair Schoene1, and Seth Burgess2 ABSTRACT There is an apparent temporal correlation between large igneous province (LIP) emplacement and global envi- ronmental crises, including mass extinctions. Advances in the precision and accuracy of geochronology in the past decade have significantly improved estimates of the timing and duration of LIP emplacement, mass extinc- tion events, and global climate perturbations, and in general have supported a temporal link between them. In this chapter, we review available geochronology of LIPs and of global extinction or climate events. We begin with an overview of the methodological advances permitting improved precision and accuracy in LIP geochro- nology. We then review the characteristics and geochronology of 12 LIP/event couplets from the past 700 Ma of Earth history, comparing the relative timing of magmatism and global change, and assessing the chronologic support for LIPs playing a causal role in Earth’s climatic and biotic crises. We find that (1) improved geochronol- ogy in the last decade has shown that nearly all well-dated LIPs erupted in < 1 Ma, irrespective of tectonic set- ting; (2) for well-dated LIPs with correspondingly well-dated mass extinctions, the LIPs began several hundred ka prior to a relatively short duration extinction event; and (3) for LIPs with a convincing temporal connection to mass extinctions, there seems to be no single characteristic that makes a LIP deadly. Despite much progress, higher precision geochronology of both eruptive and intrusive LIP events and better chronologies from extinc- tion and climate proxy records will be required to further understand how these catastrophic volcanic events have changed the course of our planet’s surface evolution.
    [Show full text]
  • Three Hotspot Reference Frames – Shallow and Lithospherically Controlled – Reflect “Mesoplates”, a Plate Tectonics Heuristic
    Three Hotspot Reference Frames – Shallow and Lithospherically Controlled – Reflect “Mesoplates”, a Plate Tectonics Heuristic Submitted to: Penrose Conference- Plume IV: Beyond the Plume Hypothesis, Iceland, 2003 May 1, 2003 (Not to be circulated beyond the organizing committee) Rex H. Pilger, Jr. Landmark Graphics Corporation 1805 Shea Center Drive Suite 400 Highlands Ranch, Colorado 80129 United States of America Extended Abstract The hotspot reference frames of the Atlantic-Indian Ocean and the Pacific Ocean are kinematically distinct. Relative motion of the two reference frames in the Late Cretaceous and Early Tertiary corresponds with motion of the American plates in the Atlantic-Indian Ocean frame, suggesting a lithospheric control on the reference frames. A third reference frame, beneath Iceland and Eurasia, cannot be satisfactorily quantified at this time, but the inability to fit Iceland in either of the two other reference frames implies its existence. The two hotspot reference frames can be shown to be relatively shallow. Hotspot traces, cross- grain oceanic gravity lineations of the Pacific Ocean reflect a shallow hotspot reference frame. Intracontinental stress fields of North America correspond with the Atlantic-Indian Ocean reference frame, also reflecting a shallow reference frame. Pacific evidence: Minor hotspot island-seamount chains of the Pacific plate (Figure 1) are controlled by lithospheric structure. Almost every such trace appears to originate on the south side of a fracture zone separating older lithosphere on the north from younger lithosphere on the south. Assuming that older plate is thicker than younger plate, passage of a fracture zone separating lithosphere of contrasting age and thickness over the asthenosphere and deeper mesosphere would result in isostatic rise of affected portions of both layers.
    [Show full text]
  • Experimental Partitioning of Rb, Cs, Sr, and Ba Between Alkali Feldspar and Peraluminous Melt
    American Mineralogist, Volume 81, pages 719-734,1996 Experimental partitioning of Rb, Cs, Sr, and Ba between alkali feldspar and peraluminous melt JONATHAN IcENHOWER AND DAVID LoNDON School of Geology and Geophysics, University of Oklahoma, 100 East Boyd Street, SEC 810, Norman, Oklahoma 73019, U.S.A. ABSTRACT Hydrous partial melting experiments performed between 650 and 750 °C at 200 MPa (H20) on synthetic metapelite compositions (quartz + albite + muscovite + biotite min- eral mixtures) doped with Ba, Sr, Rb, and Cs yielded alkali feldspar crystals with a wide range of compositions in equilibrium at their rims with peraluminous melt. Measured partition coefficients for normally trace lithophile elements between feldspar and melt [D(M)FSP/gl,M = Ba, Sr, Rb, Cs] do not depend on either temperature or bulk composition of melt for the compositions studied. Values of D(Sr)FSP/glare between 10 and 14 and appear to be independent of the albite and orthoclase contents of the feldspar crystals. In contrast, values of D(Ba)FSP/gland D(Rb)FsP/glare strongly dependent on the orthoclase content of feldspar, relationships that can be expressed by the following linear equations: D(Ba)FSP/gl= 0.07 + 0.25(orthoclase) and D(Rb)FsP/gl= 0.03 + 0.0 1(orthoclase), where orthoclase is in mole percent. These equations reproduce the range of previously reported values for D(Ba) and D(Rb) determined on natural and synthetic samples. A single par- tition coefficient for Cs was also determined at D(CS)Fsp/gl= 0.13. These data can be used in conjunction with recently published partition coefficients for muscovite, biotite, and plagioclase feldspars (Blundy and Wood 1991; Icenhower and London 1995) to model quantitatively the trace element signatures of peraluminous mag- mas during anatexis and crystallization.
    [Show full text]
  • Using Rare Earth Elements to Model Silicate Melting and Crystallization
    Using Rare Earth Elements to Model Silicate Melting and Crystallization The Rare Earth Elements (REE) The lanthanide series is formed by filling of 4f orbitals, and its constituents are commonly termed the rare earth elements (REE). The common valence state is +3 for all REE over a wide range of oxygen fugacity; Ce+4 can occur in highly oxidized environments at the earth's surface, and Eu+2 in reducing environments in the crust and mantle. The rare earth elements are lithophile elements (low electronegativities lead to the formation of highly ionic bonds), which substitute into many silicates and phosphates. Ionic radii of the lanthanides decreases with increasing atomic number from La to Lu, the lanthanide contraction… Because of their high charge and large radii, the rare earth elements are usually relatively incompatible in silicate minerals. However, due to the lanthanide contraction, the heavier rare earths are smaller and thus can "fit" within some lattice sites (although there must be charge compensation for the 3+ valence), so incompatibility decreases with increasing Z. Class Discussion #1: What mineral lattice sites could host the heavy rare earth elements? What about Eu2+? REE diagrams If we plot the concentrations of the rare earth elements as a group on a diagram of abundance versus atomic number, we observe two cosmochemical phenomena: 1) the decrease in absolute abundance with increasing atomic number; 2) the “even-odd effect” in relative abundances (higher abundances of even atomic number elements). Because these cosmochemical effects are common to all terrestrial rocks, we would rather ignore them in order to accentuate more subtle variations in absolute and relative concentrations of REE between samples.
    [Show full text]
  • Trace Elements in Igneous Petrology
    Trace Elements in igneous petrology •Abundances of trace elements are used to test petrogenetic hypotheses •No universal definition of TE: Concentration usually less than 100 ppm, often < 10 ppm •Useful trace elements: a)First transition series: Sc Ti V Cr Mn Fe Co Ni Cu Zn Ti and Fe are usually major elements, Cr, Mn, and Ni are minor elements Progressive filling of 3d orbitals Variable crystal field stabilization Commonly multivalent (Sc3, Ti4,3, V2,3,4,5, Cr2,3,6, Mn2,3, Fe2,3, Co2, Ni2 b) Lanthanides (REE): La Ce Pr Nd (Pm) Sm Eu Gd Tb Dy Ho Er Tm Yb Lu Light REE and heavy REE (Y behaves like a HREE) normalization factors (chondrites) 1 Eu2+ REE Chondritic abundances Lanthanide Contraction odd vs. even abundances 1.2 .8 .6 1.1 .4 Eu3+ Ionic radius (Å) Ionic radius Abundance (ppm) .2 Based on 8-fold 1.0 coordination 0 La Ce Pr Nd Sm Eu Gd Tb Dy Ho Er Tm Yb Lu La Ce Pr Nd Pm Sm Eu Gd Tb Dy Ho Er Tm Yb Lu (c) Large Ion Lithophile Elements (LILE): may also be partitioned into fluid phase Alkalis: K Rb Cs (monovalent) Alkaline earths: Ba Sr (divalent) Actinides: U, Th, Ra, Pa (multiple valency) (d) High field strength elements (HFSE): small, highly-charged ions Zr, Hf (4 valent) Nb, Ta (4 and 5 valent) (e) Chalcophile elements: Cu, Zn, Pb, Ag, Hg, PGE, (Fe, Co, Ni) (f) Siderophile elements: Fe, Ni, Co, Ge, P, Ga, Au (PGE)… • Decoupled from major elements: lack of stoichiometric constraints (not strictly true) • Goldschmidt’s Rules • Generalities: Incompatible elements are elements that tend to be excluded from common minerals (olivines, pyroxenes, garnets, feldspars, oxides…) in equilibrium with a melt, i.e., they have low D values.
    [Show full text]
  • High Seas Deep-Sea Fishing Grounds in the South East Atlantic Ocean 51
    50 Worldwide review of bottom fisheries in the high seas MAP 1 High seas deep-sea fishing grounds in the South East Atlantic Ocean 51 South East Atlantic Ocean FAO Statistical Area 47 (and a portion of 34) GEOGRAPHIC DESCRIPTION OF THE REGION Angola, Namibia and South Africa are the three countries bordering the South East Atlantic Region (FAO Statistical Area 47) along the African coast. This region extends from the Central Atlantic in the north at 6°S to the Southern Ocean in the south at 50°S. The western limit of the South East Atlantic is the 20°W meridian, which means that the southern Mid-Atlantic Ridge is within the region, at around 15°W, and extends over the entire region from north to south. Other important bottom topographic features in this region are the Walvis Ridge and the Valdivia Bank, joining the exclusive economic zone (EEZ) of Tristan da Cunha on the northern part of the Namibian continental shelf at around 18°S, and in the southern part, the Meteor Rise and the Agulhas Ridge. These are the areas largely targeted in the deep-sea bottom fisheries in the region, together with associated or isolated seamounts areas such as Ewing and Molloy Seamounts, Vema Seamount and those in SEAFO Subdivision A1 (SEAFO, 2007a). It is important to note that in the South East Atlantic, the continental shelf along the coasts does not extend beyond the EEZs of the coastal states. MANAGEMENT REGIME APPLICABLE TO DEEP-SEA BOTTOM FISHERIES IN THE HIGH SEAS Regional Fisheries Management Organization/Arrangement The South East Atlantic Fisheries Organisation (SEAFO) was established in 2003 with the entry into force of the Convention on the conservation and management of fisheries resources in the South East Atlantic Ocean.
    [Show full text]
  • The Geodynamic Development of the Rio Grande Rise and Walvis Ridge, Central South Atlantic Ocean, from Crustal Thickness Mapping
    Geophysical Research Abstracts Vol. 21, EGU2019-11012, 2019 EGU General Assembly 2019 © Author(s) 2019. CC Attribution 4.0 license. The Geodynamic Development of the Rio Grande Rise and Walvis Ridge, Central South Atlantic Ocean, from Crustal Thickness Mapping Michelle Graça (1,3), Nick Kusznir (2), and Natasha Stanton (3) (1) Geological Survey of Brazil - CPRM, 404, Pasteur Avenue, Urca, Rio de Janeiro, Brazil, (2) Department of Earth & Ocean Sciences, University of Liverpool, Liverpool L69 3BX, UK, (3) Faculty of Oceanography, Rio de Janeiro State University, Rio de Janeiro, Brazil The recent report of the discovery from submersible sampling of continental material of Proterozoic age on the Rio Grande Rise suggests that the formation processes of the Rio Grande Rise and Walvis Ridge in the southern S. Atlantic need to be re-examined. Existing proposed formation processes involve ocean ridge – mantle plume interaction or simply excess ‘on-ridge’ magmatism. We use gravity anomaly inversion to map crustal thickness for the central South Atlantic area encompassing the Rio Grande Rise, Walvis Ridge and adjacent South American and African rifted continental margins. We show that the Rio Grande Rise consists of three distinct bodies of anomalously thick crust (Western, Central and Eastern) separated by normal thickness oceanic crust. The Central Rio Grande Rise forms a large elliptical body with maximum crustal thickness of 25 km and Walvis Ridge also has a maximum crustal thickness of 25 km but has a narrower and more linear geometry. We use plate reconstructions to restore maps of crustal thickness and magnetic anomaly to Early Cretaceous times to examine the development of the Rio Grande Rise and Walvis Ridge.
    [Show full text]
  • Aula 4 – Tipos Crustais Tipos Crustais Continentais E Oceânicos
    14/09/2020 Aula 4 – Tipos Crustais Introdução Crosta e Litosfera, Astenosfera Crosta Oceânica e Tipos crustais oceânicos Crosta Continental e Tipos crustais continentais Tipos crustais Continentais e Oceânicos A interação divergente é o berço fundamental da litosfera oceânica: não forma cadeias de montanhas, mas forma a cadeia desenhada pela crista meso- oceânica por mais de 60.000km lineares do interior dos oceanos. A interação convergente leva inicialmente à formação dos arcos vulcânicos e magmáticos (que é praticamente o berço da litosfera continental) e posteriormente à colisão (que é praticamente o fechamento do Ciclo de Wilson, o desparecimento da litosfera oceânica). 1 14/09/2020 Curva hipsométrica da terra A área de superfície total da terra (A) é de 510 × 106 km2. Mostra a elevação em função da área cumulativa: 29% da superfície terrestre encontra-se acima do nível do mar; os mais profundos oceanos e montanhas mais altas uma pequena fração da A. A > parte das regiões de plataforma continental coincide com margens passivas, constituídas por crosta continental estirada. Brito Neves, 1995. Tipos crustais circunstâncias geométrico-estruturais da face da Terra (continentais ou oceânicos); Característica: transitoriedade passar do Tempo Geológico e como forma de dissipar o calor do interior da Terra. Todo tipo crustal adveio de um outro ou de dois outros, e será transformado em outro ou outros com o tempo, toda esta dança expressando a perda de calor do interior para o exterior da Terra. Nenhum tipo crustal é eterno; mais "duráveis" (e.g. velhos Crátons de de "ultra-longa duração"); tipos de curta duração, muitas modificações e rápida evolução potencial (como as bacias de antearco).
    [Show full text]
  • Implications of Subduction Rehydration for Earth's Deep Water
    Implications of Subduction Rehydration for Earth’s Deep Water Cycle Lars Rüpke Physics of Geological Processes, University of Oslo, Oslo, Norway, and SFB 574 Volatiles and Fluids in Subduction Zones, Kiel, Germany Jason Phipps Morgan Cornell University, Ithaca, New York, USA and SFB 574 Volatiles and Fluids in Subduction Zones, Kiel, Germany Jacqueline Eaby Dixon RSMAS/MGG, University of Miami, Miami, Florida, USA The “standard model” for the genesis of the oceans is that they are exhalations from Earth’s deep interior continually rinsed through surface rocks by the global hydrologic cycle. No general consensus exists, however, on the water distribution within the deeper mantle of the Earth. Recently Dixon et al. [2002] estimated water concentrations for some of the major mantle components and concluded that the most primitive (FOZO) are significantly wetter than the recycling associated EM or HIMU mantle components and the even drier depleted mantle source that melts to form MORB. These findings are in striking agreement with the results of numerical modeling of the global water cycle that are presented here. We find that the Dixon et al. [2002] results are consistent with a global water cycle model in which the oceans have formed by efficient outgassing of the mantle. Present-day depleted mantle will contain a small volume fraction of more primitive wet mantle in addition to drier recycling related enriched components. This scenario is consis- tent with the observation that hotspots with a FOZO-component in their source will make wetter basalts than hotspots whose mantle sources contain a larger fraction of EM and HIMU components.
    [Show full text]