DOCSLIB.ORG

2.2 Plate Tectonics Page 2 of 28

Total Page：16

File Type：pdf, Size：1020Kb

Download full-text PDF Read full-text
2.2 Plate Tectonics Page 2 of 28 Student: ………………………… Date received: ……………… Handout 7 of 14 (Topic 2.2) Plate Tectonics Earth (http://veimages.gsfc.nasa.gov/2429/globe_east_2048.jpg) Global Processes Plate Tectonics Key Ideas Intended Student Learning Plate Tectonics Continental drift provides evidence to support the Explain how continental drift is supported by theory of plate tectonics. matching: • the margins of continents; • the continuation of geological structures; • rock types and fossils; • palaeoclimatic zones on widely separated continents. Explain how the evidence given above was used to reconstruct Gondwana. Sea-floor spreading results in the generation of Explain how each of the following forms of new oceanic crust at mid-ocean ridges. evidence supports the observation that new oceanic crust is being generated at mid-ocean ridges: • Palaeomagnetic striping • Symmetry of age • Thickness of sediment. The plate tectonics theory is a model that Describe, by means of well-labelled diagrams, the explains global tectonics in terms of the processes that occur at the following types of generation and subduction of lithospheric plate plate boundary: material. • Constructive or divergent • Conservative or transform • Destructive, convergent, or collisional: Oceanic–oceanic Oceanic–continental Continental–continental. Explain the contribution of each type of boundary to the overall movement of the plates, and describe the forms of igneous and earthquake activity that occur. Explain how the existence of a Benioff zone contributes to the understanding of the process of subduction. Discuss mechanisms that have been suggested as explanations of plate movement. Topic 2.2 Plate Tectonics Page 2 of 28 2.2 - Global Processes PLATE TECTONICS Above: Plate motion based on Global Positioning System (GPS) data by NASA (http://en.wikipedia.org/wiki/Plate_tectonics). Topic 2.2 Plate Tectonics Page 3 of 28 Continental Drift The idea of continental drift - that the continents have not always occupied their present-day positions but have moved across Earth - led to the theory of plate tectonics. This theory explains why the continents have moved, and are still moving. Many features of widely separated continents can be matched, providing evidence that the continents were once joined together. Matching Continental Margins The edges of the continental shelves (not the actual coastlines) fit together like the pieces of a jigsaw puzzle. Africa and South America provide the best evidence of matching continental shelves. Continuation of Geological Structures Geological structures, such as fold mountain ranges, continue from one continent to another, although the continents are now many thousands of kilometres apart. For example, the Adelaide Orogenic Belt (or Adelaide Geosyncline) continues into Antarctica. Rock Types and Fossils Fossils of a late Palaeozoic reptile, Mesosaurus, have been found on both sides of the South Atlantic Ocean, but nowhere else in the world. If Mesosaurus were able to swim well enough to cross the ocean we would expect that its fossils were more widespread. Since it is confined to the two locations shown in the diagram, we must assume that Africa and South America were joined when this reptile was alive. Topic 2.2 Plate Tectonics Page 4 of 28 Above: Fossil Evidence for continental drift (http://en.wikipedia.org/wiki/Continental_drift) Dinosaur remains found in Australia show that the same types of dinosaurs existed here as in the rest of the world. (e.g. the copy of an Allosaurus skeleton in the Adelaide museum was made from remains found in America. Only a fossilised Allosaurus anklebone indicates that it once lived in what is now Australia.) Palaeoclimatic Zones Evidence of extreme cold or warm conditions can also be used to help establish the fact that the present-day continents have moved through geological time. 1. Rocks showing evidence of the Permian glaciation, such as those at Victor Harbor and Port Elliot, are now widely distributed on continents that are separated by thousands of kilometres, as shown in the adjacent map. If the southern continent of Gondwana is reconstructed by fitting these continents together, there is evidence that a single huge ice cap existed during the Permian. Topic 2.2 Plate Tectonics Page 5 of 28 2. Coal is found in Antarctica. Obviously neither tropical nor temperate swamps and/or forests could exist in today's Antarctic climate. Reconstruction of Gondwana What did Earth look like near the close of the Proterozoic eon? Below is a reconstruction of the southern hemisphere at 550 Ma (http://en.wikipedia.org/wiki/Gondwana), the time of the Ediacaran fauna. The above evidence indicates that, at about 200 Ma, all Earth’s land masses were joined to form a supercontinent, Pangaea. This broke into two continental blocks, the smaller supercontinents of Laurasia and Gondwana. Gondwana, consisted of the present land masses of Australia, Antarctica, India, South America and Africa. Eventually this landmass began to break into the continents we know today. The final separation, between Australia and Antarctica occurred at approximately 50 Ma. Topic 2.2 Plate Tectonics Page 6 of 28 Above: Sequence of maps showing how the supercontinent Pangaea began to separate at approximately 225 Ma (Source: http://geology.com/pangea.htm). Sea Floor Spreading Plate tectonics theory proposes that a process known as sea floor spreading causes movement of the continents. New oceanic crust is continually generated at mid-ocean ridges forcing the existing crust to move away from the ridge. Three major lines of evidence support this concept. Topic 2.2 Plate Tectonics Page 7 of 28 Symmetry of Age The age of the ocean floor basalt increases with increasing distance from the mid-ocean ridges. It also increases symmetrically on either side of a ridge. This provides evidence that basalt is continually being produced at mid-ocean ridges, as shown in the above diagram. Nowhere is the age of the ocean floor greater than 200 million years. Above: Age of ocean floor (http://en.wikipedia.org/wiki/Sea_floor_spreading) Thickness of Sediment It has been found that the distribution of deep-water sediments (as distinct from sediments derived from the land) follows a similar pattern in all oceans. The thickness of sediments increases with distance from each mid-ocean ridge, and this pattern is symmetrical on both sides of the ridge, providing further Topic 2.2 Plate Tectonics Page 8 of 28 evidence that the ocean floor near the mid-ocean ridges is very young, while the age of the floor increases with increasing distance from the ridge. Magnetic Striping on the Ocean Floor Earth possesses a magnetic field - a region where forces are exerted on magnetic materials, such as iron. Earth’s magnetic field is similar to that of a bar magnet. In other words, Earth behaves as if it has a bar magnet at its centre. The adjacent diagram shows the pattern of lines of force of Earth’s magnetic field. Igneous rocks show the direction of Earth's magnetic field at the time of their formation. As magma or lava cools, grains of magnetic minerals (e.g. magnetite, ilmenite) align themselves in the direction of Earth's magnetic field. Drill cores recovered from the ocean floor show that Earth's magnetic field has reversed many times in the past several million years. Some of the cores' "slices" indicate that the North Pole was in its present position when the sediments were laid down. We call this a time of normal polarity. Other "slices" indicate that, when the sediments were laid down, the South magnetic pole was where the North Pole is today. We call this a time of reverse polarity. Periods of normal and reverse polarity have alternated, at irregular intervals, throughout much of Earth's history. No clear reasons for these reversals are known. Topic 2.2 Plate Tectonics Page 9 of 28 A magnetic anomaly is a small change in Earth's magnetic field that may be detected by an instrument called a magnetometer, carried in a plane. A magnetic anomaly is detected when a magnetometer passes from a region in which igneous rocks solidified during a period of normal magnetic polarity (i.e. as it is today) to one in which the rocks solidified during a time or reverse polarity. In 1961, a magnetic survey off the coast of North America showed a pattern of magnetic anomaly stripes over the floor of the Atlantic Ocean. The stripes show that some of the ocean floor basalt was formed when Earth's magnetic field was as it is today - normal polarity - while adjacent 'stripes' of basalt were formed during periods when the magnetic poles were reversed. This pattern continues along the whole length of the ridge, and is symmetrical on both sides of the ridge, indicating the basalt is actually formed along the ridge. Similar magnetic anomaly patterns are associated with all mid-ocean ridges. Topic 2.2 Plate Tectonics Page 10 of 28 Therefore magnetic striping on the ocean floor provides evidence that the sea floor is spreading away from the mid-ocean ridges and explains how the continents move. New oceanic crust is formed when basalt erupts along the ridges, and existing crust is forced away from the ridge, causing sea floor spreading. Discovery of magnetic striping on the ocean floor in the 1960s was historically very significant to the development of plate tectonic theory, because it suggested a mechanism by which the continents can move. During the 1920s Alfred Wegener, a meteorologist, collected and published evidence for continental drift, but he had not been believed - partly because he could not suggest a mechanism by which the continents could move. Magnetic striping, leading to the idea of sea floor spreading, provided the missing evidence! The Theory of Plate Tectonics The plate tectonics theory encompasses the following major ideas: • The outer 50 to 150 km of Earth (i.e.
Load more

Recommended publications
  • A Continuous Plate-Tectonic Model Using Geophysical Data to Estimate
    GEOPHYSICAL JOURNAL INTERNATIONAL, 133, 379–389, 1998 1 A continuous plate-tectonic model using geophysical data to estimate plate margin widths, with a seismicity based example Caroline Dumoulin1, David Bercovici2, Pal˚ Wessel Department of Geology & Geophysics, School of Ocean and Earth Science and Technology, University of Hawaii, Honolulu, 96822, USA Summary A continuous kinematic model of present day plate motions is developed which 1) provides more realistic models of plate shapes than employed in the original work of Bercovici & Wessel [1994]; and 2) provides a means whereby geophysical data on intraplate deformation is used to estimate plate margin widths for all plates. A given plate’s shape function (which is unity within the plate, zero outside the plate) can be represented by analytic functions so long as the distance from a point inside the plate to the plate’s boundary can be expressed as a single valued function of azimuth (i.e., a single-valued polar function). To allow sufficient realism to the plate boundaries, without the excessive smoothing used by Bercovici and Wessel, the plates are divided along pseudoboundaries; the boundaries of plate sections are then simple enough to be modelled as single-valued polar functions. Moreover, the pseudoboundaries have little or no effect on the final results. The plate shape function for each plate also includes a plate margin function which can be constrained by geophysical data on intraplate deformation. We demonstrate how this margin function can be determined by using, as an example data set, the global seismicity distribution for shallow (depths less than 29km) earthquakes of magnitude greater than 4.
    [Show full text]
  • Sterngeryatctnphys18.Pdf
    Tectonophysics 746 (2018) 173–198 Contents lists available at ScienceDirect Tectonophysics journal homepage: www.elsevier.com/locate/tecto Subduction initiation in nature and models: A review T ⁎ Robert J. Sterna, , Taras Geryab a Geosciences Dept., U Texas at Dallas, Richardson, TX 75080, USA b Institute of Geophysics, Dept. of Earth Sciences, ETH, Sonneggstrasse 5, 8092 Zurich, Switzerland ARTICLE INFO ABSTRACT Keywords: How new subduction zones form is an emerging field of scientific research with important implications for our Plate tectonics understanding of lithospheric strength, the driving force of plate tectonics, and Earth's tectonic history. We are Subduction making good progress towards understanding how new subduction zones form by combining field studies to Lithosphere identify candidates and reconstruct their timing and magmatic evolution and undertaking numerical modeling (informed by rheological constraints) to test hypotheses. Here, we review the state of the art by combining and comparing results coming from natural observations and numerical models of SI. Two modes of subduction initiation (SI) can be identified in both nature and models, spontaneous and induced. Induced SI occurs when pre-existing plate convergence causes a new subduction zone to form whereas spontaneous SI occurs without pre-existing plate motion when large lateral density contrasts occur across profound lithospheric weaknesses of various origin. We have good natural examples of 3 modes of subduction initiation, one type by induced nu- cleation of a subduction zone (polarity reversal) and two types of spontaneous nucleation of a subduction zone (transform collapse and plumehead margin collapse). In contrast, two proposed types of subduction initiation are not well supported by natural observations: (induced) transference and (spontaneous) passive margin collapse.
    [Show full text]
  • Environmental Geology Chapter 2 -‐ Plate Tectonics and Earth's Internal
    Environmental Geology Chapter 2 - Plate Tectonics and Earth’s Internal Structure • Earth’s internal structure - Earth’s layers are defined in two ways. 1. Layers defined By composition and density o Crust-Less dense rocks, similar to granite o Mantle-More dense rocks, similar to peridotite o Core-Very dense-mostly iron & nickel 2. Layers defined By physical properties (solid or liquid / weak or strong) o Lithosphere – (solid crust & upper rigid mantle) o Asthenosphere – “gooey”&hot - upper mantle o Mesosphere-solid & hotter-flows slowly over millions of years o Outer Core – a hot liquid-circulating o Inner Core – a solid-hottest of all-under great pressure • There are 2 types of crust ü Continental – typically thicker and less dense (aBout 2.8 g/cm3) ü Oceanic – typically thinner and denser (aBout 2.9 g/cm3) The Moho is a discontinuity that separates lighter crustal rocks from denser mantle below • How do we know the Earth is layered? That knowledge comes primarily through the study of seismology: Study of earthquakes and seismic waves. We look at the paths and speeds of seismic waves. Earth’s interior boundaries are defined by sudden changes in the speed of seismic waves. And, certain types of waves will not go through liquids (e.g. outer core). • The face of Earth - What we see (Observations) Earth’s surface consists of continents and oceans, including mountain belts and “stable” interiors of continents. Beneath the ocean, there are continental shelfs & slopes, deep sea basins, seamounts, deep trenches and high mountain ridges. We also know that Earth is dynamic and earthquakes and volcanoes are concentrated in certain zones.
    [Show full text]
  • Plate Tectonics and the Cycling of Earth Materials
    Plate Tectonics and the cycling of Earth materials Plate tectonics drives the rock cycle: the movement of rocks (and the minerals that comprise them, and the chemical elements that comprise them) from one reservoir to another Arrows are pathways, or fluxes, the I,M.S rocks are processes that “reservoirs” - places move material from one reservoir where material is temporarily stored to another We need to be able to identify these three types of rocks. Why? They convey information about the geologic history of a region. What types of environments are characterized by the processes that produce igneous rocks? What types of environments are preserved by the accumulation of sediment? What types of environments are characterized by the tremendous heat and pressure that produces metamorphic rocks? How the rock cycle integrates into plate tectonics. In order to understand the concept that plate tectonics drives the rock cycle, we need to understand what the theory of plate tectonics says about how the earth works The major plates in today’s Earth (there have been different plates in the Earth’s past!) What is a “plate”? The “plate” of plate tectonics is short for “lithospheric plate” - - the outermost shell of the Earth that behaves as a rigid substance. What does it mean to behave as a rigid substance? The lithosphere is ~150 km thick. It consists of the crust + the uppermost mantle. Below the lithosphere the asthenosphere behaves as a ductile layer: one that flows when stressed It means that when the substance undergoes stress, it breaks (a non-rigid, or ductile, substance flows when stressed; for example, ice flows; what we call a glacier) Since the plates are rigid, brittle 150km thick slabs of the earth, there is a lot of “action”at the edges where they abut other plates We recognize 3 types of plate boundaries, or edges.
    [Show full text]
  • 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.
    [Show full text]
  • Plate Tectonics
    Plate tectonics tive motion determines the type of boundary; convergent, divergent, or transform. Earthquakes, volcanic activity, mountain-building, and oceanic trench formation occur along these plate boundaries. The lateral relative move- ment of the plates typically varies from zero to 100 mm annually.[2] Tectonic plates are composed of oceanic lithosphere and thicker continental lithosphere, each topped by its own kind of crust. Along convergent boundaries, subduction carries plates into the mantle; the material lost is roughly balanced by the formation of new (oceanic) crust along divergent margins by seafloor spreading. In this way, the total surface of the globe remains the same. This predic- The tectonic plates of the world were mapped in the second half of the 20th century. tion of plate tectonics is also referred to as the conveyor belt principle. Earlier theories (that still have some sup- porters) propose gradual shrinking (contraction) or grad- ual expansion of the globe.[3] Tectonic plates are able to move because the Earth’s lithosphere has greater strength than the underlying asthenosphere. Lateral density variations in the mantle result in convection. Plate movement is thought to be driven by a combination of the motion of the seafloor away from the spreading ridge (due to variations in topog- raphy and density of the crust, which result in differences in gravitational forces) and drag, with downward suction, at the subduction zones. Another explanation lies in the different forces generated by the rotation of the globe and the tidal forces of the Sun and Moon. The relative im- portance of each of these factors and their relationship to each other is unclear, and still the subject of much debate.
    [Show full text]
  • The Ocean Basin & Plate Tectonics
    Sept. 2010 MAR 110 HW 3: 1 Homework 3: The Ocean Basin & Plate Tectonics 3-1. THE OCEAN BASIN The world ocean basin is an extensive suite of connected depressions (or basins) that are filled with salty water; covering 72% of the Earth’s surface. The ocean basin bathymetric profile in Figure 3-1 highlights features of a typical ocean basin, which is bordered by continental margins at the ocean’s edge. Starting at the coast, the sea floor the slopes slightly across the continental shelf to the shelf break where it plunges down the steeper continental slope to continental rise and the abyssal plain, which is flat because accumulated sediments. The continental shelf is the flooded edge of the continent -extending from the beach to the shelf break, with typical depths ranging from 130 m to 200 m. The sea floor slopes over wide shelves are 1° to 2° - virtually flat- and somewhat steeper over narrower shelves. Continental shelves are generally gently undulating surfaces, sometimes interrupted by hills and valleys (see Figure 3-2). Sept. 2010 MAR 110 HW 3: 2 The continental slope connects the continental shelf to the deep ocean, with typical depths of 2 to 3 km. While appearing steep in these vertically exaggerated pictures, the bottom slopes of a typical continental slope region are modest angles of 4° to 6°. Continental slope regions adjacent to deep ocean trenches tend to descend somewhat more steeply than normal. Sediments derived from the weathering of the continental material are delivered by rivers and continental shelf flow to the upper continental slope region just beyond the continental shelf break.
    [Show full text]
  • This Dynamic Earth in January of 1992
    View of the planet Earth from the Apollo spacecraft. The Red Sea, which separates Saudi Arabia from the continent of Africa, is clearly visible at the top. (Photograph courtesy of NASA.) Contents Preface Historical perspective Developing the theory Understanding plate motions "Hotspots": Mantle Some unanswered questions Plate tectonics and people Endnotes thermal plumes 1 of 77 2002-01-01 11:52 This pdf-version was edited by Peter Lindeberg in December 2001. Any deviation from the original text is non-intentional. This book was originally published in paper form in February 1996 (design and coordination by Martha Kiger; illustrations and production by Jane Russell). It is for sale for $7 from: U.S. Government Printing Office Superintendent of Documents, Mail Stop SSOP Washington, DC 20402-9328 or it can be ordered directly from the U.S. Geological Survey: Call toll-free 1-888-ASK-USGS Or write to USGS Information Services Box 25286, Building 810 Denver Federal Center Denver, CO 80225 303-202-4700; Fax 303-202-4693 ISBN 0-16-048220-8 Version 1.08 The online edition contains all text from the original book in its entirety. Some figures have been modified to enhance legibility at screen resolutions. Many of the images in this book are available in high resolution from the USGS Media for Science page. USGS Home Page URL: http://pubs.usgs.gov/publications/text/dynamic.html Last updated: 01.29.01 Contact: [email protected] 2 of 77 2002-01-01 11:52 In the early 1960s, the emergence of the theory of plate tectonics started a revolution in the earth sciences.
    [Show full text]
  • Ocean Drilling Program Initial Reports Volume
    1. INTRAPLATE DEFORMATION AND BENGAL FAN SEDIMENTATION: BACKGROUND AND OBJECTIVES1 Shipboard Scientific Party2 INTRODUCTION 4. To establish the provenance of the terrigeneous sediments and to use compositional variations to document the tectonic Classical plate tectonics assumes that large lithospheric uplift history of the Himalayas; plates behave as rigid units, with deformation confined primar- 5. To understand the relationship between fault zones, bed- ily to their boundaries. Observational evidence suggests, how- ding planes, and the flow of water deduced from surface heat ever, that the Indian-Australian Plate is not behaving in this flow measurements; manner, but has been subjected to significant internal compres- 6. To investigate the effects of the regional compressive stress sion (Fig. 1). This is evidenced by an unusually large number regime and high heat flow on the physical, hydrological, and of intraplate earthquakes, many with thrust focal mechanisms magnetic properties of the sediment and on the diagenetic pro- (Sykes, 1970; Banghar, 1972; Fitch et al., 1973; Stein and Okal, cess; and 1978; Bergman et al., 1984) and by the inability of plate motion 7. To investigate depositional processes and rates through models to successfully reproduce both spreading rates and direc- time and the growth of the Bengal Fan, by obtaining a section tions along the boundaries of the Indian plate (Minster and Jor- deposited prior to the onset of intraplate deformation. dan, 1978; Wiens et al., 1985). However, the most spectacular and direct evidence for internal deformation in the Indian plate GEOLOGICAL AND GEOPHYSICAL are E-W striking large-scale folds and small high-angle faults in BACKGROUND the wide region between the Central Indian Ridge and the Ninety- The collision between continental India and Eurasia, begin- east Ridge (Eittreim and Ewing, 1972; Weissel et al., 1980).
    [Show full text]
  • Plate Tectonics
    Plate Tectonics Introduction Continental Drift Seafloor Spreading Plate Tectonics Divergent Plate Boundaries Convergent Plate Boundaries Transform Plate Boundaries Summary This curious world we inhabit is more wonderful than convenient; more beautiful than it is useful; it is more to be admired and enjoyed than used. Henry David Thoreau Introduction • Earth's lithosphere is divided into mobile plates. • Plate tectonics describes the distribution and motion of the plates. • The theory of plate tectonics grew out of earlier hypotheses and observations collected during exploration of the rocks of the ocean floor. You will recall from a previous chapter that there are three major layers (crust, mantle, core) within the earth that are identified on the basis of their different compositions (Fig. 1). The uppermost mantle and crust can be subdivided vertically into two layers with contrasting mechanical (physical) properties. The outer layer, the lithosphere, is composed of the crust and uppermost mantle and forms a rigid outer shell down to a depth of approximately 100 km (63 miles). The underlying asthenosphere is composed of partially melted rocks in the upper mantle that acts in a plastic manner on long time scales. Figure 1. The The asthenosphere extends from about 100 to 300 km (63-189 outermost part of miles) depth. The theory of plate tectonics proposes that the Earth is divided lithosphere is divided into a series of plates that fit together like into two the pieces of a jigsaw puzzle. mechanical layers, the lithosphere and Although plate tectonics is a relatively young idea in asthenosphere. comparison with unifying theories from other sciences (e.g., law of gravity, theory of evolution), some of the basic observations that represent the foundation of the theory were made many centuries ago when the first maps of the Atlantic Ocean were drawn.
    [Show full text]
  • Explanatory Notes for the Plate-Tectonic Map of the Circum-Pacific Region
    U.S. DEPARTMENT OF THE INTERIOR TO ACCOMPANY MAP SHEETS OF THE U.S. GEOLOGICAL SURVEY CIRCUM-PACIFIC PLATE-TECTONIC MAP SERIES Explanatory Notes for the Plate-Tectonic Map of the Circum-Pacific Region By GEORGE W. MOORE CIRCUM-PACIFIC COUNCIL_a t ENERGY AND MINERAL \il/ RESOURCES THE ARCTIC SHEET OF THIS SERIES IS AVAILABLE FROM U.S. GEOLOGICAL SURVEY MAP DISTRIBUTION BOX 25286, FEDERAL CENTER, DENVER, COLORADO 80225, USA OTHER SHEETS IN THIS SERIES AVAILABLE FROM THE AMERICAN ASSOCIATION OF PETROLEUM GEOLOGISTS BOX 979 TULSA, OKLAHOMA 74101, USA 1992 CIRCUM-PACIFIC COUNCIL FOR ENERGY AND MINERAL RESOURCES Michel T. Halbouty, Chair CIRCUM-PACIFIC MAP PROJECT John A. Reinemund, Director George Gryc, General Chair Explanatory Notes to Supplement the PLATE-TECTONIC MAP OF THE CIRCUM-PACIFIC REGION Jose Corvalan Dv Chair, Southeast Quadrant Panel lan W.D. Dalziel, Chair, Antarctic Panel Kenneth J. Drummond, Chair, Northeast Quadrant Panel R. Wallace Johnson, Chair, Southwest Quadrant Panel George W. Moore, Chair, Arctic Panel Tomoyuki Moritani, Chair, Northwest Quadrant Panel TECTONIC ELEMENTS George W. Moore, Department of Geosciences, Oregon State University, Corvallis, Oregon, USA Nikita A. Bogdanov, Institute of the Lithosphere, Academy of Sciences, Moscow, Russia Jose Corvalan, Servicio Nacional de Geologia y Mineria, Santiago, Chile Campbell Craddock, Department of Geology and Geophysics, University of Wisconsin, Madison, Wisconsin H. Frederick Doutch, Bureau of Mineral Resources, Canberra, Australia Kenneth J. Drummond, Mobil Oil Canada, Ltd., Calgary, Alberta, Canada Chikao Nishiwaki, Institute for International Mineral Resources Development, Fujinomiya, Japan Tomotsu Nozawa, Geological Survey of Japan, Tsukuba, Japan Gordon H. Packham, Department of Geophysics, University of Sydney, Australia Solomon M.
    [Show full text]
  • How Plate Tectonics Clicked
    COMMENT use for understanding cells that do not NOAA communicate using electrical impulses. It is this view that has perpetuated our comparative ignorance about glia. Moreover, the exclusion of glia from the BRAIN Initiative underscores a more general problem with the project: the assumption that enough measuring of enough neurons will in itself uncover ‘emergent’ properties and, ultimately, cures for diseases1,4. Rather than simply materializing from measurements of “every spike from every neuron”1,4, better understanding and new treatments will require hypothesis-directed research. The 302 neurons and 7,000 connections that make up the nervous system of the roundworm Caenorhabditis elegans were mapped in the 1970s and 80s. More than two decades later, little is understood about how the worm’s nervous system produces complex behaviours. In any major mapping expedition, the first priority should be to survey the uncharted regions. Our understanding of one half of the brain (the part comprised of astrocytes, oligodendrocytes and microglia) lags a century behind our knowledge of neurons. I believe that answers to questions about the brain and public support for a large-scale study are more likely to come from expanding the search into this unknown territory. As a first step, tools such as optogenetic meth- ods and mathematical models are needed to assess the number, distribution and properties of different kinds of glial cell The US research vessel Explorer towed a magnetometer to map fields over the sea floor in 1960. in different brain regions, and to identify how glia communicate with each other and with neurons, and what developmen- tal and physiological factors affect this.
    [Show full text]