DOCSLIB.ORG

Oceanic Spreading Center

Total Page：16

File Type：pdf, Size：1020Kb

Download full-text PDF Read full-text

Load more

North-South Variations in Structure, Topography, and Melting Regime along the Ultra-Slow Spreading Red Sea Ridge by Emilie Elisabeth Bowman B.S. Geological Sciences (2017) University of Texas at Austin Submitted to the Department of Earth, Atmospheric, and Planetary Sciences in partial fulfillment of the requirements for the degree of Master of Science in Geology at the MASSACHUSETTS INSTITUTE OF TECHNOLOGY June 2019 C 2019 Massachusetts Institute of Technology. All rights reserved. Author............................................Signature redacted Department of Earth, Atmospheric, and Planetary Sciences May 22, 2019 Signature redacted C ertified b y . ..................................................................... ..... .. .... ,. .. .- Oliver Jagoutz Associate o ssor of Geology Signature redacted hesis Supervisor Accepted by.................... ................................. Robert D. van der Hilst MASSACHUSES INSTITUTE Schlumberger Professor of Earth and Planetary Sciences Of T.ECHNOLOGY Department Head JUN 17 2019 LIBRARIES ARCHIVES 2 North-South Variations in Structure, Topography, and Melting Regime along the Ultra-Slow Spreading Red Sea Ridge by Emilie Elisabeth Bowman Submitted to the Department of Earth, Atmospheric, and Planetary Sciences on May 22, 2019 in partial fulfillment of the requirements for the degree of Master of Science in Geology Abstract The Red Sea rift is a nascent ultra-slow spreading ridge superimposed on the Afar plume. Based on high-resolution seismic data, the southernmost (south of the Danakil rift at 17.05'N), southern (17.05-19.75 0N), and central (19.75-23.8 0N) segments display seafloor spreading that is anomalously magma-rich compared to other ultra-slow spreading centers. In contrast, the northern segment (23.8-280N) exhibits magma-poor extension along large-offset east- and west-dipping detachments. Sediment-corrected basement depths along the northern Red Sea reveal an axial valley as deep as the Gakkel Ridge (4200-5100 m). South of 19.75 0N, plume-supported axial shoaling matches that of adjacent parts of Arabia, Africa, and the Gulf of Aden. Geochemically, the southernmost Red Sea is the locus of plume-ridge interaction. Here, E-MORBs are enriched in alkali, incompatible, and light rare-earth elements. High mantle potential temperatures (Tp; 1326 5'C), melting pressures (12 0 kbars) and temperatures (1306 6'C), and fractionation pressures (5.3 1.6 kbars) calculated using the reverse fractional crystallization model of Brown (2019) suggest thickened oceanic crust created by high-degree partial melting of a plume-like source. North of the Danakil rift, Tp (1307+ 1"C) spans a narrow range and is within the range of ambient mantle. The southern Red Sea contains N- to E-MORB depleted in alkali, incompatible, and light rare-earth elements indicating limited mixing with Afar plume material, while the central segment is host to the most depleted magmas along the ridge (La/SmN 0.8). Within the southern and central regions, fractionation pressures (2.0 1.2 and 4.8 2.1 kbars, respectively) indicate lithosphere (5-15 km) thinner than that of normal ultra-slow spreading ridges (15-35 km). In the northern Red Sea, high Na8 and deep pressures of melting (10.4 1.4 kbars) suggest thickened lithosphere, undulations in which induce melt focusing into volcanic deeps. Based on these results, we propose that the Red Sea south of at least 26.5 0N is an oceanic spreading center. We find that anomalously magma-rich spreading in the central and southern segments cannot be related to the Afar plume. Instead, the Danakil rift diverts plume-related mantle flow northeast beneath Arabia. Thus, the southern and central Red Sea must be characterized by vigorous mantle upwelling that causes heightened melt production and lithospheric thinning. Thesis Supervisor: Oliver Jagoutz Title: Associate Professor of Geology 3 4 Table of Contents A b strac t ........................................................................................................................................... 3 Table of Contents ............................................................................................................................ 5 List of Figures ................................................................................................................................. 6 L st of Tables .................................................................................................................................. 6 1. Introduction................................................................................................................................. 7 2. Background and Previous W ork .............................................................................................. 8 2.1. Geologic Setting................................................................................................................... 8 2.2. The Red Sea ....................................................................................................................... 12 3. Structure of the Red Sea Rift .................................................................................................. 15 3.1. M aterials and M ethods....................................................................................................... 15 3.2. Southern Red Sea............................................................................................................... 15 3.3. Central Red Sea.................................................................................................................. 18 3.4. N orthern Red Sea............................................................................................................... 20 3.4.1. N ature of the Basem ent in the N orthern Red Sea ................................................... 26 4. Com position of A xial Basalts from the Red Sea Ridge....................................................... 31 4.1. Previous W ork ................................................................................................................... 31 4.2. Red Sea G eochem istry ....................................................................................................... 34 4.2.1. M ajor Elem ents...........................................................................................................34 4.2.2. M ajor Elem ent D ifferentiation................................................................................. 42 4.2.3. V ariations in M antle Source along the Red Sea Ridge.......................................... 43 5. Changes in M elting Regim e along the Red Sea Ridge ......................................................... 50 5.1. Results of the Maximum Likelihood Reverse Fractional Crystallization Model ....... 52 5.1.1. Calculated Prim ary M elt Com positions.................................................................. 61 5.1.2. Major Element Oxide Compositions of Basalts from the Red Sea Compared to Other U ltra-Slow Spreading Ridges ............................................................................................... 63 6. The Effect of Plume-Ridge Interaction on the Topography of the Red Sea and Surrounding R e g io n s ......................................................................................................................................... 6 4 7. D iscussion................................................................................................................................. 70 7.1. The N orthern Red Sea as an U ltra-Slow Spreading Ridge ............................................ 71 7.2. Central and Southern Red Sea ....................................................................................... 79 7.3. Plume Influence Beneath Ramad Seamount and the Southern Islands .......................... 84 7.4. Role of the D anakil Rift in D iverting Plum e Flow ......................................................... 85 8. Conclusions............................................................................................................................... 86 References ..................................................................................................................................... 88 5 List of Figures Figure 1. M ap of the R ed Sea region ........................................................................................... 9 Figure 2. Map of the southern and central Red Sea................................................................. 17 Figure 3. M ap of the northern Red Sea..................................................................................... 21 Figure 4. Interpretations of representative seismic lines from the Red Sea............................... 22 Figure 5. Topographic profile of the Red Sea axial ridge......................................................... 29 Figure 6. Red Sea axial basalt sample location map.................................................................. 35 Figure 7. Total alkali (Na20 + K 20) versus SiO 2 diagram...................................................... 36 Figure 8. K/Ti versus M gO diagram ......................................................................................... 38 Figure 9. M ajor elem ent oxides versus M gO............................................................................ 39 Figure 10. Variations in Na8 , K/Ti, Nb/Zr, and La/SmN of axial basalts along the Red Sea........ 44 Figure 11. Variations in isotopic signatures of axial basalts along the Red Sea .....................
Recommended publications
  • Seamount Abundances and Abyssal Hill Morphology on the Eastern

    Seamount Abundances and Abyssal Hill Morphology on the Eastern

    GEOPHYSICALRESEARCH LETTERS, VOL. 24, NO. 15,PAGES 1955-1958, AUGUST 1, 1997 Seamountabundances and abyssalhill morphology on the eastern flank of the East Pacific Rise at 14øS IngoGrevemeyer, 12Vincent Renard, 3Claudia Jennrich, • and Wilfried Weigel I Abstract. Bathymetricdata from a Hydrosweepmultibeam hills. Abyssalhills in the PacificOcean form. primarily sonarsurvey of a 720 km longtectonic corridor on theeast througha complexcombination of volcanicconstructional flank of the southernEPR at 14ø14'S coveredabout 25,000 processesand faulting that occur at or nearthe ridgeaxis km2 of zero-ageto 8.5 m.y. old crust(magnetic anomaly [e.g., Golf, 1991; MacdonaMet al., 1996]. Stochastic 4A). In this corridorwe documenta strongcorrelation of analysisof abyssalhills have shownthat ridge flank robustalong flowline changes in abyssalhill morphologyroughness increases with decreasing spreading rate [Menard, and seamountsize distributionwith spreadingrate changes 1967;Malinverno, 199l; Goff, 199l]. Nevertheless,seafloor deducedfrom our magneticdata. Indeed, we find thatboth roughnessvalues show a largevariation along a single rmsheight of abyssalhills andabundance and height of spreadingsegment [Golf, 1991; Goffet al., 1993],suggesting seamountsincrease significantly as spreadingrate changes that spreadingrate cannotbe the solefactor governing from ~ 75 mm/yrto over 85 mm/yr(half rate). Moreover, variationsin abyssalhill morphology. we identified 46 seamountstaller than !.00 m. Previous From November 8 to December 30, 1995 the R/V Sonne studieson the southernEPR reporteda larger densityof carriedout the EXCO-cruise,a geophysicalsurvey on zero- seamounts,organized primarily in chains.Our investigation, age to about8.5 m.y. old seafloor created at the"superfast" however, revealed seamountsnot associatedwith major spreading(full rate >140 mm/yr) East Pacific Rise south of chains,leading us to theconclusion that different forms of the Garrettfracture zone [Weigelet al., 1996].
  • Modeling Seafloor Spreading Adapted from a Lesson Developed by San Lorenzo USD Teachers: Julie Ramirez, Veenu Soni, Marilyn Stewart, and Lawrence Yano (2012)

    Modeling Seafloor Spreading Adapted from a Lesson Developed by San Lorenzo USD Teachers: Julie Ramirez, Veenu Soni, Marilyn Stewart, and Lawrence Yano (2012)

    Teacher Instruction Sheet Modeling Seafloor Spreading Adapted from a lesson developed by San Lorenzo USD Teachers: Julie Ramirez, Veenu Soni, Marilyn Stewart, and Lawrence Yano (2012) Teacher Background The process of seafloor spreading created the seafloor of the oceans. For example, in the Atlantic Ocean, North America and South America moved away from Europe and Africa and the resulting crack was filled by mantle material, which cooled and formed new lithosphere. The process continues today. Molten mantle materials continually rise to fill the cracks formed as the plates move slowly apart from each other. This process creates an underwater mountain chain, known as a mid-ocean ridge, along the zone of newly forming seafloor. Molten rock erupts along a mid-ocean ridge, then cools and freezes to become solid rock. The direction of the magnetic field of the Earth at the time the rock cools is "frozen" in place. This happens because magnetic minerals in the molten rock are free to rotate so that they are aligned with the Earth's magnetic field. After the molten rock cools to a solid rock, these minerals can no longer rotate freely. At irregular intervals, averaging about 200-thousand years, the Earth's magnetic field reverses. The end of a compass needle that today points to the north will instead point to the south after the next reversal. The oceanic plates act as a giant tape recorder, preserving in their magnetic minerals the orientation of the magnetic field present at the time of their creation. Geologists call the current orientation "normal" and the opposite orientation "reversed." USGS Teacher Instruction Sheet In the figure above, two plates are moving apart.
  • Description of Map Units Northeast Asia Geodynamics Map

    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.
  • 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

    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.
  • Effusive and Explosive Volcanism on the Ultraslow-Spreading Gakkel Ridge, 85�E

    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.
  • Quaternary Stratigraphy of the Northwind Ridge, Arctic Ocean

    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.
  • Seafloor Spreading and Plate Tectonics

    Seafloor Spreading and Plate Tectonics

    OCN 201: Seafloor Spreading and Plate Tectonics I Revival of Continental Drift Theory • Kiyoo Wadati (1935) speculated that earthquakes and volcanoes may be associated with continental drift. • Hugo Benioff (1940) plotted locations of deep earthquakes at edge of Pacific “Ring of Fire”. • Earthquakes are not randomly distributed but instead coincide with mid-ocean ridge system. • Evidence of polar wandering. Revival of Continental Drift Theory Wegener’s theory was revived in the 1950’s based on paleomagnetic evidence for “Polar Wandering”. Earth’s Magnetic Field Earth’s magnetic field simulates a bar magnet, but it is caused by A bar magnet with Fe filings convection of liquid Fe in Earth’s aligning along the “lines” of the outer core: the Geodynamo. magnetic field A moving electrical conductor induces a magnetic field. Earth’s magnetic field is toroidal, or “donut-shaped”. A freely moving magnet lies horizontal at the equator, vertical at the poles, and points toward the “North” pole. Paleomagnetism in Rocks • Magnetic minerals (e.g. Magnetite, Fe3 O4 ) in rocks align with Earth’s magnetic field when rocks solidify. • Magnetic alignment is “frozen in” and retained if rock is not subsequently heated. • Can use paleomagnetism of ancient rocks to determine: --direction and polarity of magnetic field --paleolatitude of rock --apparent position of N and S magnetic poles. Apparent Polar Wander Paths • Geomagnetic poles 200 had apparently 200 100 “wandered” 100 systematically with time. • Rocks from different continents gave different paths! Divergence increased with age of rocks. 200 100 Apparent Polar Wander Paths 200 200 100 100 Magnetic poles have never been more the 20o from geographic poles of rotation; rest of apparent wander results from motion of continents! For a magnetic compass, the red end of the needle points to: A.
  • Seafloor Spreading and Subduction Zones

    Seafloor Spreading and Subduction Zones

    Name: ___________________________________________ Period: __________ Date: __________________ Seafloor Spreading and Subduction Zones Directions: The diagram on the reverse side depicts an area of the ocean floor where different plates are shifting due to plate tectonics. Begin by labeling the parts (draw an arrow to indicate which feature you mean). Then answer the questions below. You may use your book and whatever notes you have. I. Label the following parts: 2 oceanic plates 2 trenches 1 continental plate mid-ocean ridge 1 oceanic/continental plate transform fault (intersecting the ridge) use brackets mountains (on land) rising magma (in 2 places) island arc II. Further Analysis: 1) Identify the plate boundaries by placing a big letter “D” above the divergent boundary and placing a “C” above each convergent boundary. (Each letter should go in the dotted box.) 2) What process is taking place along the ridge? _______________________________ What process is taking place at the trenches? _______________________________ 3) During subduction, a(n) _________________ plate will sink beneath the continental plate. 4) What causes one plate to sink while another floats? 5) Using a green colored pencil, shade in the area where the youngest ocean rocks would be found with regard to seafloor spreading. Then, in blue, shade in the area of oldest ocean rock. Which of these areas (green or blue) would have the thickest sediment sitting on top of it, AND why? 6) Using a red colored pencil, color in 2 areas of lithosphere where you would find melting rock. What happens to the melted rock, and what landforms does it produce? 7) On your diagram, draw circular arrows to show the circulation of the magma beneath the mid-ocean ridge.
  • OCN 201 Seafloor Spreading and Plate Tectonics Question

    OCN 201 Seafloor Spreading and Plate Tectonics Question

    9/6/2018 OCN 201 Seafloor Spreading and Plate Tectonics Question What was wrong from Wegener’s theory of continental drift? A. The continents were once all connected in a single supercontinent B. The continents slide over ocean floor C. The continents are still moving today D. All of them are correct 1 9/6/2018 Tectonics theories Tectonics: a branch of geology that deals with the major structural (or deformational) features of the Earth and their origin, relationships, and history Late 19th century • Shrinking Earth theory: mountain ranges formed from the contraction and cooling of Earth’s surface • Expansion of the Earth due to heating: to explain why continents are broken up Vertical motion 20th century A new way of thinking about the Earth! • Continental drift theory • Seafloor spreading theory Horizontal motion • Plate tectonics theory Earth’s Magnetic Field A bar magnet with Fe Earth’s magnetic field simulates filings aligning along a bar magnet, but is caused by the “lines” of the convection of Fe in the outer magnetic field core: the Geodynamo… 2 9/6/2018 Earth’s Magnetic Field • Earth’s magnetic field is Dip angle = 90 toroidal, or “donut-shaped” • A freely moving magnet lies horizontal at the equator, vertical at the poles, and points toward the “North” pole • Magnetic inclination: angle between the magnet and Earth’s surface • By measuring the inclination Dip angle = 0 and the angle to the magnetic pole, one can tell position on the Earth relative to the magnetic poles Paleomagnetism • Igneous rock contains magnetic minerals,
  • Lesson Outline for Teaching

    Lesson Outline for Teaching

    Lesson Outline for Teaching Lesson 2: Development of a Theory A. Mapping the Ocean Floor 1. Scientists mapped the depth of the ocean floor using a device called a(n) echo sounder. 2. In the middle of the oceans are large mountain ranges called mid-ocean ridges. a. Existence of these mountain ranges was confirmed through echo-sounder research. b. These underwater mountain ranges are much longer than mountain ranges on land. B. Seafloor Spreading 1. Seafloor spreading occurs when new oceanic crust forms at a mid-ocean ridge and old crust moves away from the ridge. a. Molten rock, or magma, rises from the mantle through cracks in the crust. It erupts as lava from volcanic vents along the mid-ocean ridge. b. The molten rock cools and becomes basalt, the rock that forms the oceanic crust. c. New oceanic crust forms along a mid-ocean ridge, and older crust moves away from the ridge. 2. The topography of the seafloor includes the abyssal plain and rugged mountains. a. The rugged mountains that make up the mid-ocean ridge can form in different ways. One way is through large amounts of lava erupting from the center of the Companies, Inc. The McGraw-Hill of a division © Glencoe/McGraw-Hill, Copyright ridge, cooling, and building up around the ridge. Another way is through upward-moving magma pushing on the crust above it, causing it to crack and form jagged, angular mountains on the seafloor. b. Eventually, sediment forms on top of the oldest oceanic crust, making a smooth seafloor called the abyssal plain.
  • Drilling the Crust at Mid-Ocean Ridges

    Drilling the Crust at Mid-Ocean Ridges

    or collective redistirbution of any portion of this article by photocopy machine, reposting, or other means is permitted only with the approval of Th e Oceanography Society. Send all correspondence to: [email protected] or Th eOceanography PO Box 1931, Rockville, USA.Society, MD 20849-1931, or e to: [email protected] Oceanography correspondence all Society. Send of Th approval portionthe ofwith any articlepermitted only photocopy by is of machine, reposting, this means or collective or other redistirbution articleis has been published in Th SPECIAL ISSUE FEATURE Oceanography Drilling the Crust Threproduction, Republication, systemmatic research. for this and teaching article copy to use in reserved. e is rights granted All OceanographyPermission Society. by 2007 eCopyright Oceanography Society. journal of Th 20, Number 1, a quarterly , Volume at Mid-Ocean Ridges An “in Depth” perspective BY BENOÎT ILDEFONSE, PETER A. RONA, AND DONNA BLACKMAN In April 1961, 13.5 m of basalts were drilled off Guadalupe In the early 1970s, almost 15 years after the fi rst Mohole Island about 240 km west of Mexico’s Baja California, to- attempt, attendees of a Penrose fi eld conference (Confer- gether with a few hundred meters of Miocene sediments, in ence Participants, 1972) formulated the concept of a layered about 3500 m of water. This fi rst-time exploit, reported by oceanic crust composed of lavas, underlain by sheeted dikes, John Steinbeck for Life magazine, aimed to be the test phase then gabbros (corresponding to the seismic layers 2A, 2B, for the considerably more ambitious Mohole project, whose and 3, respectively), which themselves overlay mantle perido- objective was to drill through the oceanic crust down to tites.
  • Discovery of a Black Smoker Vent Field and Vent Fauna at the Arctic Mid-Ocean Ridge

    Discovery of a Black Smoker Vent Field and Vent Fauna at the Arctic Mid-Ocean Ridge

    ARTICLE Received 17 May 2010 | Accepted 27 Oct 2010 | Published 23 Nov 2010 DOI: 10.1038/ncomms1124 Discovery of a black smoker vent field and vent fauna at the Arctic Mid-Ocean Ridge Rolf B. Pedersen1,2, Hans Tore Rapp1,3, Ingunn H. Thorseth1,2, Marvin D. Lilley4, Fernando J.A.S. Barriga5, Tamara Baumberger6, Kristin Flesland1,2, Rita Fonseca5,7, Gretchen L. Früh-Green7 & Steffen L. Jorgensen1,3 The Arctic Mid-Ocean Ridge (AMOR) represents one of the most slow-spreading ridge systems on Earth. Previous attempts to locate hydrothermal vent fields and unravel the nature of venting, as well as the provenance of vent fauna at this northern and insular termination of the global ridge system, have been unsuccessful. Here, we report the first discovery of a black smoker vent field at the AMOR. The field is located on the crest of an axial volcanic ridge (AVR) and is associated with an unusually large hydrothermal deposit, which documents that extensive venting and long-lived hydrothermal systems exist at ultraslow-spreading ridges, despite their strongly reduced volcanic activity. The vent field hosts a distinct vent fauna that differs from the fauna to the south along the Mid-Atlantic Ridge. The novel vent fauna seems to have developed by local specialization and by migration of fauna from cold seeps and the Pacific. 1 Centre for Geobiology, University of Bergen, 5007 Bergen, Norway. 2 Department of Earth Science, University of Bergen, 5007 Bergen, Norway. 3 Department of Biology, University of Bergen, 5007 Bergen, Norway. 4 School of Oceanography, University of Washington, Seattle, 98195-7940 Washington, USA.