Chapter 2 Plate Tectonics and the Ocean Floor

Essential of Oceanography

Table of Contents

Chapter Overview

  1. Much evidence supports plate tectonics theory.
  2. The plate tectonics model describes features and processes on Earth.
  3. Plate tectonic science has applications to Earth Science studies.
  4. Configuration of land and oceans has changed in the past and will continue to change into the future.

Plate Tectonics

  • Alfred Wegener first proposed in 1912
  • Called it “Continental Drift”

Evidence for Continental Drift

  • Wegener proposed Pangaea – one large continent existed 200 million years ago
  • Panthalassa – one large ocean
    • Included the Tethys Sea
  • Noted puzzle-like fit of modern continents
  • Puzzle-like fit corroborated in 1960s
  • Sir Edward Bullard used computer models to fit continents.
  • Matching sequences of rocks and mountain chains
  • Similar rock types, ages, and structures on different continents
  • Glacial ages and other climate evidence
  • Evidence of glaciation in now tropical regions
  • Direction of glacial flow and rock scouring
  • Plant and animal fossils indicate different climate than today.
  • Distribution of organisms
  • Same fossils found on continents that today are widely separated
  • Modern organisms with similar ancestries

Objections to Early Continental Drift Model

  • 1915 – Wegener published The Origins of Continents and Oceans
    • Suggested continents plow through ocean basins
  • Met with hostile criticism and open ridicule
  • Tidal gravitational attractions too small to move continents
  • Proposed mechanism defies laws of physics

Evidence for Plate Tectonics

  • New evidence from World War II
  • Sea floor studies with sonar
  • New technology enabled study of Earth’s magnetic field
  • Earth’s magnetic field and paleomagnetism
  • Earth has magnetic polarity
  • North and South polarities
  • Magnetic polarity recorded in igneous rocks
    • Magnetite in basalt
  • Paleomagnetism –study of Earth’s ancient magnetic field
    • Interprets where rocks first formed
    • Magnetic dip
  • Apparent polar wandering
  • Location of North Pole changed over time
  • Magnetic dip data

Earth’s Magnetic Pole

Magnetic Polarity Reversals

  • Earth’s magnetic polarity reverses periodically
  • Recorded in ancient igneous rocks
  • 176 reversals in past 76 million years
  • Unpredictable pattern

Paleomagnetism and the Ocean Floor

  • 1955 – deep water rock mapping
  • Magnetic anomalies – regular pattern of north-south magnetism “stripes”
  • Stripes were symmetrical about long underwater mountain range

Sea Floor Spreading

  • Harry Hess
    • World War II submarine captain and geologist
  • Depth recordings show sea floor features History of Ocean Basins
    • Seafloor spreading
    • Mantle convection cells as driving mechanism

Plate Tectonic Processes

Sea Floor Spreading

  • Mid-ocean ridge – spreading center
  • Subduction zones – oceanic trench site of crust destruction
  • Subduction can generate deep ocean trenches.

Sea Floor Spreading Evidence

  • Frederick Vine and Drummond Matthews (1963)
  • Analysis of igneous rock stripes around mid-ocean ridge
  • Sea floor stripes record Earth’s magnetic polarity

Age of Ocean Floor

  • Late 1960s deep-sea drilling
  • Radiometric dating of ocean rocks
  • Symmetric pattern of age distribution about mid-ocean ridges
  • Oldest ocean floor only 180 million years old

Heat Flow

  • Heat flow – heat from Earth’s interior released to surface
  • Very high at mid-ocean ridges
  • Low at subduction zones

Earthquakes as Evidence

  • Most large earthquakes occur at subduction zones.
  • Earthquake activity mirrors tectonic plate boundaries.

Global Plate Boundaries

Plate Tectonics Theory

  • Lithosphere – tectonic plates that float on ductile asthenosphere
  • Large-scale geologic features occur at plate boundaries.
  • Two major tectonic forces
    • Slab pull
    • Slab suction

Types of Plate Boundaries

Examples of Plate Boundaries

Characteristics, Tectonic Processes, Features, and Examples of Plate Boundaries

Plate Boundary TypePlate MovementCrust TypesSea Floor Created or Destroyed?Tectonic ProcessSea Floor FeaturesGeographic Examples
Divergent Plate BoundariesApart (↔)Oceanic-oceanicNew sea floor is createdSea floor spreadingMid-ocean ridge; volcanoes; young lava flowsMid-Atlantic Ridge, East Pacific Rise
Continental-continentalNew sea floor created as continent splits apartContinental riftingRift valley; volcanoes; young lava flowsEast Africa Rift Valleys, Red Sea, Gulf of California
Convergent Plate BoundariesTogether (→←)Oceanic-continentalOld sea floor is destroyedSubductionTrench; volcanic arc on landPeru–Chile Trench, Andes Mountains
Oceanic-oceanicOld sea floor is destroyedSubductionTrench; volcanic arc as islandsMariana Trench, Aleutian Islands
Continental-continentalN/ACollisionTall mountainsHimalaya Mountains, Alps
Transform Plate BoundariesPast each other (→↔)OceanicN/ATransform faultingFaultMendocino Fault, Eltanin Fault (between mid-ocean ridges)
ContinentalN/ATransform faultingFaultSan Andreas Fault, Alpine Fault (New Zealand)

Divergent Boundary Features

  • Plates move apart
  • Mid-ocean ridge
    • Rift valley
  • New ocean floor created
  • Shallow focus earthquakes
    • Intensity measured with seismic moment magnitude

Divergent Plate Boundary

Generation of a Divergent Boundary

Formation of a Rift Valley

Types of Spreading Centers

  • Oceanic rise
    • Fast-spreading
    • Gentle slopes
    • East Pacific
  • Oceanic ridge
    • Slow-spreading
    • Steep slopes
    • Mid-Atlantic
  • Ultra-slow
    • Deep rift valley
    • Widely scattered volcanoes
    • Arctic and southwest India

Convergent Boundary Features

  • Plates move toward each other Oceanic crust destroyed
    • Ocean trench
    • Volcanic arc
  • Deep focus earthquakes
    • Great forces involved
    • Mineral structure changes associated

Three Types of Convergent Boundaries

Types of Convergent Boundaries

  • Oceanic-Continental Convergence
    • Ocean plate is subducted
    • Continental arcs generated
    • Explosive andesitic volcanic eruptions
  • Oceanic-Oceanic Convergence
    • Denser plate is subducted
    • Deep trenches generated
    • Volcanic island arcs generated
  • Continental-Continental Convergence
    • No subduction
    • Tall mountains uplifted
  • Himalayas from India-Asia collision

Transform Boundary Features

  • Offsets oriented perpendicular to mid-ocean ridge
    • Segments of plates slide past each other
  • Offsets permit mid-ocean ridge to move apart at different rates
  • Shallow but strong earthquakes
  • Oceanic Transform Fault – ocean floor only
  • Continental Transform Fault –cuts across continent
    • San Andreas Fault
  • Transform faults occur between mid-ocean ridge segments.

Applications of Plate Tectonics

  • Mantle Plumes and Hotspots
  • Intraplate features
    • Volcanic islands within a plate
    • Island chains
  • Record ancient plate motions
  • Nematath – hotspot track

Global Hotspot Locations

Hawaiian Island – Emperor Seamount Nematath

Plate Tectonics and Intraplate Features

  • Seamounts
    • Rounded tops
  • Tablemounts or guyots
    • Flattened tops
  • Subsidence of flanks of mid-ocean ridge
  • Wave erosion may flatten seamount.

Coral Reef Development

  • Fringing reefs –develop along margin of landmass
  • Barrier reefs –separated from landmass by lagoon
  • Atolls – reefs continue to grow after volcanoes are submerged

Great Barrier Reef Records Plate Movement

Detecting Plate Motion with Satellites

Paleogeography

  • Paleogeography – study of ancient continents Continental accretion
    • Continental material added to edges of continents through plate motion
  • Pangaea – 540 million to 300 million years ago

Breakup of Pangaea

  • 180 million years ago – Pangaea separated
    • N. and S. America rifted from Europe and Africa
    • Atlantic Ocean forms
  • 120 million years ago – S. America and Africa clearly separated
  • 45 million years ago – India starts Asia collision
    • Australia moving north from Antarctica

Future Predictions

  • Assume same direction and rate of plate motions as now
    • Atlantic will enlarge, Pacific will shrink
    • New sea from East Africa rift valleys
    • Further Himalaya uplift
    • Separation of North and South America
    • Part of California in Alaska

World Map 50 million Years in Future

Wilson Cycle

  • John Tuzo Wilson
  • Plate tectonics model shows life cycle of ocean basins
    • Formation
    • Growth
    • Destruction

REFFERENCE- Essentials of Oceanography by Alan P. Trujillo and Harold V. Thurman (11th edition)

Reference: All images and content are taken from Essentials of Oceanography by Alan P. Trujillo and Harold V. Thurman, 12th Edition.

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CSIR NET Exam: EARTH, ATMOSPHERIC, OCEAN AND PLANETARY SCIENCES

Exam Pattern: EARTH, ATMOSPHERIC, OCEAN AND PLANETARY SCIENCES 

 PART APART BPART CTOTAL
Total questions205080150
Max No. of Questions to attempt15352575
Marks for each correct answer224200
Marks for each incorrect answer (Negative marking for part A & B is @ 25%, and part C is @ 33%)0.50.51.32

The candidate is required to answer a maximum of 15, 35, and 25 questions from Part-A, Part-B, and Part-C, respectively. If more than the required number of questions are answered, only the first 15, 35, and 25 questions in Part A, Part B, and Part C, respectively, will be taken up for evaluation.

Below each question in Part A, Part B, and Part C, four alternatives or responses are given. Only one of these alternatives is the “correct” option to the question. The candidate has to find, for each question, the correct or the best answer.

Syllabus

EARTH, ATMOSPHERIC, OCEAN AND PLANETARY SCIENCES

PAPER I (PART B)

  1. The Earth and the Solar System

    • Milky Way and the solar system.
    • Modern theories on the origin of the Earth and planetary bodies.
    • Earth’s orbital parameters, Kepler’s laws of planetary motion.
    • Geological Time Scale; space and time scales of processes in the solid Earth, atmosphere, and oceans.
    • Radioactive isotopes and their applications.
    • Meteorites: chemical composition and primary differentiation of the Earth.
    • Basic principles of stratigraphy.
    • Theories about the origin of life and fossil records.
    • Earth’s gravity, magnetic fields, and thermal structure: Geoid and spheroid concepts; Isostasy.
  2. Earth Materials, Surface Features, and Processes

    • Gross composition and physical properties of important minerals and rocks.
    • Properties and processes responsible for mineral concentrations.
    • Distribution of rocks and minerals in Earth’s units and India.
    • Physiography of the Earth; weathering, erosion, and soil formation.
    • Energy balance of Earth’s surface processes.
    • Physiographic features and river basins in India.
  3. Interior of the Earth, Deformation, and Tectonics

    • Basic concepts of seismology and Earth’s internal structure.
    • Physico-chemical and seismic properties of Earth’s interior.
    • Stress and strain concepts; rock deformation.
    • Folds, joints, and faults; causes and measurement of earthquakes.
    • Interplate and intraplate seismicity; paleomagnetism.
    • Sea-floor spreading and plate tectonics.
  4. Oceans and Atmosphere

    • Hypsography of continents and ocean floors: continental shelves, slopes, abyssal plains.
    • Physical and chemical properties of seawater; residence times of elements.
    • Ocean currents, waves, tides, thermohaline circulation, and conveyor belts.
    • Major water masses, biological productivity, and fluid motion.
    • Atmospheric structure and heat budget; greenhouse gases and global warming.
    • General circulation, monsoon systems, ENSO, cyclones, and local systems in India.
    • Marine and atmospheric pollution, ozone depletion.
  5. Environmental Earth Sciences

    • Properties of water and the hydrological cycle.
    • Energy resources: uses, degradation, alternatives, and management.
    • Ecology, biodiversity, and natural resource conservation.
    • Natural hazards and remote sensing applications.

PAPER I (PART C)

I. Geology

  1. Mineralogy and Petrology

    • Point group, space group, and lattice concepts.
    • Crystal field theory, mineralogical spectroscopy, and bonding in mineral structures.
    • Genesis, properties, and crystallization of magmas.
    • Metamorphic structures, textures, and thermobarometry.
    • Petrogenesis of Indian rock suites: Deccan Traps, charnockites, ophiolites, and more.
  2. Structural Geology and Geotectonics

    • Stress and strain analysis; Mohr circles.
    • Geometry and mechanics of folds, faults, and ductile shear zones.
    • Plate boundaries, mantle plumes, and Himalayan orogeny.
  3. Paleontology and Applications

    • Life origin theories, evolution models, and mass extinctions.
    • Applications of fossils in age determination, paleoecology, and paleogeography.
    • Micropaleontology in hydrocarbon exploration.
  4. Sedimentology and Stratigraphy

    • Classification of sediments and sedimentary rocks.
    • Sedimentary environments and basin evolution.
    • Stratigraphic principles, correlation methods, and sequence stratigraphy.
    • Phanerozoic stratigraphy of India.
  5. Marine Geology and Paleoceanography

    • Ocean floor morphology, ocean circulation, and thermohaline processes.
    • Factors influencing oceanic sediments and paleoceanographic reconstruction.
  6. Geochemistry

    • Atomic properties, periodic table, thermodynamics of reactions, and isotopes in geochronology.
    • Applications of stable isotopes in Earth processes.
  7. Economic Geology

    • Ore formation processes, mineral deposit studies, and petroleum geology.
    • Coal and unconventional energy resources.
  8. Precambrian Geology and Crustal Evolution

    • Evolution of Earth systems and Precambrian characteristics of India.
    • Precambrian–Cambrian boundary.
  9. Quaternary Geology

    • Quaternary stratigraphy, climate variability, and human evolution.
    • Dating methods and tectonic geomorphology.
  10. Applied Geology

  • Remote sensing and GIS.
  • Engineering properties of rocks; construction investigations.
  • Methods of mineral exploration and groundwater studies.

II. Physical Geography

  1. Geomorphology: Landform processes, DEM analysis, extraterrestrial geomorphology.
  2. Climatology: Radiation balance, wind systems, ENSO, and climate classification.
  3. Biogeography: Plant and animal associations, Indian biogeography, and conservation.
  4. Environmental Geography: Man-land relationships, hazards, and ecological balance.
  5. Geography of India: Physical geography, climatology, agriculture, and population characteristics.

III. Geophysics

  1. Signal Processing: Fourier transforms, filters, and signal analysis.
  2. Field Theory: Newtonian potential, Green’s theorem, and seismic wave propagation.
  3. Numerical Analysis and Inversion: Least squares, optimization, and pattern recognition.
  4. Gravity and Magnetic Methods: Data interpretation and anomaly analysis.
  5. Seismic Methods: Ray theory, reflection/refraction techniques, seismic stratigraphy.
  6. Well Logging: Techniques for lithology, porosity, and fluid saturation interpretation.

(IV) METEOROLOGY

1) Climatology

  • Same as under Geography.

2) Physical Meteorology

  • Thermal Structure of the Atmosphere and Its Composition.
  • Radiation:
    • Basic laws – Rayleigh and Mie scattering, multiple scattering.
    • Radiation from the sun, solar constant, effect of clouds, surface and planetary albedo.
    • Emission and absorption of terrestrial radiation, radiation windows, radiative transfer, Greenhouse effect, net radiation budget.
  • Thermodynamics of Dry and Moist Air:
    • Specific gas constant, adiabatic and isentropic processes, entropy and enthalpy.
    • Moisture variables, virtual temperature, Clausius–Clapeyron equation.
    • Adiabatic processes of moist air, thermodynamic diagrams.
  • Hydrostatic Equilibrium:
    • Hydrostatic equation, variation of pressure with height, geopotential, standard atmosphere, altimetry.
  • Vertical Stability of the Atmosphere:
    • Dry and moist air parcel and slice methods, tropical convection.
  • Atmospheric Optics:
    • Visibility and optical phenomena – rainbows, haloes, corona, mirage, etc.

3) Atmospheric Electricity

  • Fair weather electric field in the atmosphere and potential gradients.
  • Ionization in the atmosphere, electrical fields in thunderstorms.
  • Theories of thunderstorm electrification, structure of lightning flash, mechanisms of earth-atmospheric charge balance, and the role of thunderstorms.

4) Cloud Physics

  • Cloud classification, condensation nuclei, growth of cloud drops and ice-crystals.
  • Precipitation mechanisms: Bergeron–Findeisen process, coalescence process.
  • Precipitation of warm and mixed clouds, artificial precipitation, hail suppression, fog and cloud dissipation.
  • Radar observation of clouds and precipitation:
    • Radar equation, rain drop spectra, radar echoes of hailstorms, tornadoes, hurricanes, and rainfall measurements.

5) Dynamic Meteorology

  • Basic Equations and Fundamental Forces:
    • Pressure, gravity, centripetal and Coriolis forces.
    • Continuity and momentum equations (Cartesian and spherical coordinates).
    • Scale analysis, inertial flow, geostrophic and gradient winds, thermal wind.
    • Divergence and vertical motion, Rossby, Richardson, Reynolds, and Froude numbers.
  • Atmospheric Turbulence:
    • Mixing length theory, planetary boundary layer equations, Ekman layer, eddy transport of heat, moisture, and momentum.
  • Linear Perturbation Theory:
    • Internal and external gravity waves, inertia waves, gravity waves, Rossby waves, wave motion in the tropics, barotropic and baroclinic instabilities.
  • Atmospheric Energetics:
    • Kinetic, potential, and internal energies; conversion into kinetic energy; available potential energy.

6) Numerical Weather Prediction (NWP)

  • Computational instability, filtering of sound and gravity waves.
  • Filtered forecast equations, barotropic and baroclinic models.
  • Objective analysis, data assimilation techniques, satellite applications in NWP.

7) General Circulation and Climate Modelling

  • Observed zonally symmetric circulations, meridional circulation models.
  • General circulation modelling principles: grid-point and spectral GCMs.
  • Climate variability phenomena: ENSO, QBO, MJO, etc.
  • Ocean-atmosphere coupled models.

8) Synoptic Meteorology

  • Weather observations and transmission, synoptic charts.
  • Synoptic weather forecasting, prediction of weather elements, and hazardous weather phenomena.
  • Tropical Meteorology:
    • ITCZ, monsoons, tropical cyclones, jet streams.
  • Extra-Tropical Features:
    • Jet streams, extratropical cyclones, anticyclones.
  • Air masses and fronts: sources, classification, frontogenesis, and associated weather.

9) Aviation Meteorology

  • Meteorological role in aviation, weather hazards during takeoff, cruising, and landing.
  • In-flight hazards: icing, turbulence, visibility issues, gusts, wind shear, thunderstorms.

10) Satellite Meteorology

  • Polar orbiting and geostationary satellites.
  • Applications in identifying synoptic systems, cyclones, temperature estimation, rainfall prediction, and temperature/humidity soundings.

(V) OCEAN SCIENCES

1) Physical Oceanography

  • T-S diagrams, mixing processes, characteristics of water masses.
  • Wind-generated waves, shallow and deep-water wave dynamics.
  • Coastal processes: wave reflection, refraction, diffraction, littoral currents, rip currents, tsunami, and more.
  • Ocean Circulation:
    • Global conveyor belt circulation, Ekman’s theory, upwelling processes.

2) Chemical Oceanography

  • Composition of seawater, chemical exchanges, and classification of elements.
  • Element chemistry under special conditions (estuaries, vents, etc.).
  • Carbonate chemistry, biological pumps, and sedimentary deposit factors.

3) Geological Oceanography

  • Topics as listed under “Marine Geology & Paleoceanography.”

4) Biological Oceanography

  • Classification of marine environments and organisms.
  • Primary and secondary production, factors affecting biodiversity.
  • Human impacts on marine communities and climate change effects.

 

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