The Subduction Factory: How It Operates in the Evolving Earth
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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. -
INTERIOR of the EARTH / an El/EMEI^TARY Xdescrrpntion
N \ N I 1i/ / ' /' \ \ 1/ / / s v N N I ' / ' f , / X GEOLOGICAL SURVEY CIRCULAR 532 / N X \ i INTERIOR OF THE EARTH / AN El/EMEI^TARY xDESCRrPNTION The Interior of the Earth An Elementary Description By Eugene C. Robertson GEOLOGICAL SURVEY CIRCULAR 532 Washington 1966 United States Department of the Interior CECIL D. ANDRUS, Secretary Geological Survey H. William Menard, Director First printing 1966 Second printing 1967 Third printing 1969 Fourth printing 1970 Fifth printing 1972 Sixth printing 1976 Seventh printing 1980 Free on application to Branch of Distribution, U.S. Geological Survey 1200 South Eads Street, Arlington, VA 22202 CONTENTS Page Abstract ......................................................... 1 Introduction ..................................................... 1 Surface observations .............................................. 1 Openings underground in various rocks .......................... 2 Diamond pipes and salt domes .................................. 3 The crust ............................................... f ........ 4 Earthquakes and the earth's crust ............................... 4 Oceanic and continental crust .................................. 5 The mantle ...................................................... 7 The core ......................................................... 8 Earth and moon .................................................. 9 Questions and answers ............................................. 9 Suggested reading ................................................ 10 ILLUSTRATIONS -
Tectonics and Crustal Evolution
Tectonics and crustal evolution Chris J. Hawkesworth, Department of Earth Sciences, University peaks and troughs of ages. Much of it has focused discussion on of Bristol, Wills Memorial Building, Queens Road, Bristol BS8 1RJ, the extent to which the generation and evolution of Earth’s crust is UK; and Department of Earth Sciences, University of St. Andrews, driven by deep-seated processes, such as mantle plumes, or is North Street, St. Andrews KY16 9AL, UK, c.j.hawkesworth@bristol primarily in response to plate tectonic processes that dominate at .ac.uk; Peter A. Cawood, Department of Earth Sciences, University relatively shallow levels. of St. Andrews, North Street, St. Andrews KY16 9AL, UK; and Bruno The cyclical nature of the geological record has been recog- Dhuime, Department of Earth Sciences, University of Bristol, Wills nized since James Hutton noted in the eighteenth century that Memorial Building, Queens Road, Bristol BS8 1RJ, UK even the oldest rocks are made up of “materials furnished from the ruins of former continents” (Hutton, 1785). The history of ABSTRACT the continental crust, at least since the end of the Archean, is marked by geological cycles that on different scales include those The continental crust is the archive of Earth’s history. Its rock shaped by individual mountain building events, and by the units record events that are heterogeneous in time with distinctive cyclic development and dispersal of supercontinents in response peaks and troughs of ages for igneous crystallization, metamor- to plate tectonics (Nance et al., 2014, and references therein). phism, continental margins, and mineralization. This temporal Successive cycles may have different features, reflecting in part distribution is argued largely to reflect the different preservation the cooling of the earth and the changing nature of the litho- potential of rocks generated in different tectonic settings, rather sphere. -
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). -
Seismic Velocity Structure of the Continental Lithosphere from Controlled Source Data
Seismic Velocity Structure of the Continental Lithosphere from Controlled Source Data Walter D. Mooney US Geological Survey, Menlo Park, CA, USA Claus Prodehl University of Karlsruhe, Karlsruhe, Germany Nina I. Pavlenkova RAS Institute of the Physics of the Earth, Moscow, Russia 1. Introduction Year Authors Areas covered J/A/B a The purpose of this chapter is to provide a summary of the seismic velocity structure of the continental lithosphere, 1971 Heacock N-America B 1973 Meissner World J i.e., the crust and uppermost mantle. We define the crust as 1973 Mueller World B the outer layer of the Earth that is separated from the under- 1975 Makris E-Africa, Iceland A lying mantle by the Mohorovi6i6 discontinuity (Moho). We 1977 Bamford and Prodehl Europe, N-America J adopted the usual convention of defining the seismic Moho 1977 Heacock Europe, N-America B as the level in the Earth where the seismic compressional- 1977 Mueller Europe, N-America A 1977 Prodehl Europe, N-America A wave (P-wave) velocity increases rapidly or gradually to 1978 Mueller World A a value greater than or equal to 7.6 km sec -1 (Steinhart, 1967), 1980 Zverev and Kosminskaya Europe, Asia B defined in the data by the so-called "Pn" phase (P-normal). 1982 Soller et al. World J Here we use the term uppermost mantle to refer to the 50- 1984 Prodehl World A 200+ km thick lithospheric mantle that forms the root of the 1986 Meissner Continents B 1987 Orcutt Oceans J continents and that is attached to the crust (i.e., moves with the 1989 Mooney and Braile N-America A continental plates). -
Physiography of the Seafloor Hypsometric Curve for Earth’S Solid Surface
OCN 201 Physiography of the Seafloor Hypsometric Curve for Earth’s solid surface Note histogram Hypsometric curve of Earth shows two modes. Hypsometric curve of Venus shows only one! Why? Ocean Depth vs. Height of the Land Why do we have dry land? • Solid surface of Earth is Hypsometric curve dominated by two levels: – Land with a mean elevation of +840 m = 0.5 mi. (29% of Earth surface area). – Ocean floor with mean depth of -3800 m = 2.4 mi. (71% of Earth surface area). If Earth were smooth, depth of oceans would be 2450 m = 1.5 mi. over the entire globe! Origin of Continents and Oceans • Crust is formed by differentiation from mantle. • A small fraction of mantle melts. • Melt has a different composition from mantle. • Melt rises to form crust, of two types: 1) Oceanic 2) Continental Two Types of Crust on Earth • Oceanic Crust – About 6 km thick – Density is 2.9 g/cm3 – Bulk composition: basalt (Hawaiian islands are made of basalt.) • Continental Crust – About 35 km thick – Density is 2.7 g/cm3 – Bulk composition: andesite Concept of Isostasy: I If I drop a several blocks of wood into a bucket of water, which block will float higher? A. A thick block made of dense wood (koa or oak) B. A thin block made of light wood (balsa or pine) C. A thick block made of light wood (balsa or pine) D. A thin block made of dense wood (koa or oak) Concept of Isostasy: II • Derived from Greek: – Iso equal – Stasia standing • Density and thickness of a body determine how high it will float (and how deep it will sink). -
Label and Describe the Earth Diagram
Name_________________________class______ Label and Describe the Earth Diagram Read the definitions then use the information to color code, label and describe IN YOUR OWN WORDS each section of the diagram below. Definitions: crust – (green) the rigid, rocky outer surface of the Earth, composed mostly of basalt and granite. The crust is the thinnest of all layers. It is thicker on continents & thinner under the oceans. inner core – (gray) the solid iron-nickel center of the Earth that is very hot and under great pressure. mantle – (orange) a rocky layer located under the crust - it is composed of silicon, oxygen, magnesium, iron, aluminum, and calcium. Convection (heat) currents carry heat from the hot inner mantle to the cooler outer mantle. outer core – (red) the molten iron-nickel layer that surrounds the inner core. ______________________________________________ ______________________________________________ ______________________________________________ _______________________________________ _______________________________________ _______________________________________ ___________________________________ ___________________________________ ___________________________________ ___ __________________________________ __________________________________ __________________________________ __________________________ Name_________________________________cLass________ Label the OUTER LAYERS of the Earth This is a cross section of only the upper layers of the Earth’s surface. Read the definitions below and use the information to locate label and describe IN TWO WORDS the outer layers of the Earth. One has been done for you. continental crust – thick, top Continental Crust – (green) the thick parts of the Earth's crust, not located under the ocean; makes up the comtinents. Oceanic Crust – (brown) thinner more dense parts of the Earth's crust located under the oceans. Ocean – (blue) large bodies of water sitting atop oceanic crust. Lithosphere– (outline in black) made of BOTH the crust plus the rigid upper part of the upper mantle. -
Absolute Plate Motions Constrained By
JOURNAL OF GEOPHYSICAL RESEARCH, VOL. 114, B10405, doi:10.1029/2009JB006416, 2009 Click Here for Full Article Absolute plate motions constrained by shear wave splitting orientations with implications for hot spot motions and mantle flow Corne´ Kreemer1 Received 27 February 2009; revised 11 June 2009; accepted 14 July 2009; published 22 October 2009. [1] Here, I present a new absolute plate motion model of the Earth’s surface, determined from the alignment of present-day surface motions with 474 published shear wave (i.e., SKS) splitting orientations. When limited to oceanic islands and cratons, splitting orientations are assumed to reflect anisotropy in the asthenosphere caused by the differential motion between lithosphere and mesosphere. The best fit model predicts a 0.2065°/Ma counterclockwise net rotation of the lithosphere as a whole, which revolves around a pole at 57.6°S and 63.2°E. This net rotation is particularly well constrained by data on cratons and/or in the Indo-Atlantic region. The average data misfit is 19° and 24° for oceanic and cratonic areas, respectively, but the normalized root-mean-square misfits are about equal at 5.4 and 5.2. Predicted plate motions are very consistent with recent hot spot track azimuths (<8° on many plates), except for the slowest moving plates (Antarctica, Africa, and Eurasia). The difference in hot spot propagation vectors and plate velocities describes the motion of hot spots (i.e., their underlying plumes). For most hot spots that move significantly, the motions are considerably smaller than and antiparallel to the absolute plate velocity. Only when the origin depth of the plume is considered can the hot spot motions be explained in terms of mantle flow. -
Marine Science and Oceanography
Marine Science and Oceanography Marine geology- study of the ocean floor Physical oceanography- study of waves, currents, and tides Marine biology– study of nature and distribution of marine organisms Chemical Oceanography- study of the dissolved chemicals in seawater Marine engineering- design and construction of structures used in or on the ocean. Marine Science, or Oceanography, integrates different sciences. 1 2 1 The Sea Floor: Key Ideas * The seafloor has two distinct regions: continental margins and deep-ocean basins * The continental margin is the relatively shallow ocean floor near shore. It shares the structure and composition of the adjacent continent. * The deep-ocean floor differs from the continental margin in tectonic origin, history and composition. * New technology has allowed scientists to accurately map even the deepest ocean trenches. 3 Bathymetry: The Study of Ocean Floor Contours Satellite altimetry measures the sea surface height from orbit. Satellites can bounce 1,000 pulses of radar energy off the ocean surface every second. With the use of satellite altimetry, sea surface levels can be measured more accurately, showing sea surface distortion. 4 2 5 The Physiography of the Ocean Floor Physiography and bathymetry (submarine landscape) allow the sea floor to be subdivided into three distinct provinces: (1) continental margins, (2) deep ocean basins and (3) mid-oceanic ridges. 6 3 The Topography of Ocean Floors The classifications of ocean floor: Continental Margins – the submerged outer edge of a continent Ocean Basin – the deep seafloor beyond the continental margin Ocean Ridge System - extends throughout the ocean basins A typical cross section of the Atlantic ocean basin. -
Plate Boundaries - Where the Action Is! Modeling Activity
Plate Boundaries - Where the action is! Modeling Activity The Earth’s outer shell, called the lithosphere, is broken up into tectonic plates. The lithosphere is rock that is rigid and brittle - it is composed of the crust and the uppermost mantle. The rigid plates move around on top of a hotter more mobile layer of the mantle known as the asthenosphere. Where the plates meet is where most of the world’s earthquakes and volcanic activity occurs. Let’s explore what happens at different plate boundaries. What you need: • Graham crackers • Waxed paper • Peanut butter or frosting and a knife to spread • Small bowl of water PUSH Set up: • Spread peanut butter or frosting on the waxed paper. Cover an area almost twice the size of a whole graham cracker. This is the asthenosphere – soft and mobile. • Break a graham cracker in half, now you have two tectonic plates. The PULL plates are rigid and brittle. When you broke the graham cracker... you caused an earthquake! What you’ll do: Place two graham cracker halves (tectonic plates) on your asthenosphere. Using one finger on each plate, very slowly and gently move your plates around on the asthenosphere. This is how tectonic plates on the Earth’s asthe- nosphere move. Now let’s check out the different types of boundaries between plates. Divergent Plate Boundary These are boundaries where two plates move away from each other. These boundaries are often found on ocean floors. Put the two graham cracker halves (tectonic plates) touching each other in the middle of your asthenosphere. -
Continental Crust - Irina M
GEOPHYSICS AND GEOCHEMISTRY – Vol.II - Continental Crust - Irina M. Artemieva CONTINENTAL CRUST Irina M. Artemieva Uppsala University, Sweden Keywords:Anisotropy, brittle crust, composition, continental arc, continental margin, cratons, crustal thickness, crustal types, ductile crust, extended crust, juvenile crust, lower crust, Moho discontinuity, Orogens, plate tectonics, platforms, Poisson’s ratio, Rift, reflectivity, Rheology, seismic velocities, shear-wave splitting, shields, subcrustal velocity, transitional crust, upper crust, upper mantle Contents 1. Introduction 2. Methods of Continental Crust Studies 2.1 Seismic Studies 2.2 Geologic Mapping 2.3 Petrologic Studies 2.4 Heat Flow Studies 2.5 Electromagnetic Studies 2.6 Gravity Studies 2.7 Laboratory Ultrasonic Measurements 2.8 Continental Drilling 2.9 Geochronology 3. Average Seismic Structure of Continental Crust 3.1 Crustal Thickness and Seismic Velocities 3.2 Crustal Reflectivity 3.3 The Moho Discontinuity 4. Types of Continental Crust 4.1 Shields and Platforms 4.2 Collisional Orogens 4.3 Continental Rifts and Extended Crust 4.4 Continental Margins 5. Physical Properties of Continental Crust 5.1 Seismic Velocities in Typical Crustal Rocks 5.2 Seismic Anisotropy in Continental Crust 5.3 Poisson’sUNESCO Ratio – EOLSS 5.4 Crustal Density 5.5 Crustal Rheology,SAMPLE Brittle-Ductile Crust CHAPTERS 6. Composition of Continental Crust 6.1 Methods of Estimating Crustal Composition 6.2 The Upper and Middle Continental Crust 6.3 The Lower Continental Crust 7. Crustal Evolution 7.1 Hypotheses for the Continental Crust Origin 7.2 Age Distribution of Continental Crust 7.3 The Formation of Continental Crust and Mantle Dynamics Acknowledgments ©Encyclopedia of Life Support Systems (EOLSS) GEOPHYSICS AND GEOCHEMISTRY – Vol.II - Continental Crust - Irina M. -
Lithospheric Strength Profiles
21 LITHOSPHERIC STRENGTH PROFILES To study the mechanical response of the lithosphere to various types of forces, one has to take into account its rheology, which means knowing how it flows. As a scientific discipline, rheology describes the interactions between strain, stress and time. Strain and stress depend on the thermal structure, the fluid content, the thickness of compositional layers and various boundary conditions. The amount of time during which the load is applied is an important factor. - At the time scale of seismic waves, up to hundreds of seconds, the sub-crustal mantle behaves elastically down deep within the asthenosphere. - Over a few to thousands of years (e.g. load of ice cap), the mantle flows like a viscous fluid. - On long geological times (more than 1 million years), the upper crust and the upper mantle behave also as thin elastic and plastic plates that overlie an inviscid (i.e. with no viscosity) substratum. The dimensionless Deborah number D, summarized as natural response time/experimental observation time, is a measure of the influence of time on flow properties. Elasticity, plastic yielding, and viscous creep are therefore ingredients of the mechanical behavior of Earth materials. Each of these three modes will be considered in assessing flow processes in the lithosphere; these mechanical attributes are expressed in terms of lithospheric strength. This strength is estimated by integrating yield stress with depth. The current state of knowledge of rock rheology is sufficient to provide broad general outlines of mechanical behavior but also has important limitations. Two very thorny problems involve the scaling of rock properties with long periods and for very large length scales.