EAR 110 1st Edition Lecture 6Outline of Previous Lecture:I. Review of previous conceptsII. Plate tectonicsIII. Three types of relative plate motionsOutline of Current Lecture:I. Divergent Boundary ReviewII. Ocean-Ocean convergent boundaryIII. Ocean-Continent Convergent boundaryIV. Continent-continent convergenceV. Transform BoundaryVI. Plate MovementVII. Geometry of plate boundariesVIII. Earth’s Magnetic FieldIX. Evidence for plate tectonicsX. Formation of linear islands and seamount chainsXI. Why is South America lopsided?Lecture 6: 1/29/2015Ch 3: Plate Tectonics Cont. I. Divergent boundary reviewa. Initial uplift from rising mantleb. Stretching and faulting form rift (ex. East Africa)c. Melting forms magmad. Seafloor spreading and new ocean basin (ex. Red Sea)e. Ocean widens with spreading (ex. Atlantic Ocean)II. Ocean-Ocean convergent boundarya. Definition: two oceanic plate move toward each otherb. One plate moves down and get subducted beneath the otheri. This subducted slab releases water, which causes melting of magma (adding water to a rock composition reduces its melting point)ii. The melted magma rises through the mantle and crust, eruptions form volcanic arcs 1. Example: Japan, Aleutian Islands2. Island arc = the beginning of a continent; partially melting oceanic crust creates continental crust. From iron and magnesium rich crust to silica rich crustIII. Ocean-Continent Convergent boundarya. Definition: oceanic and continental plates convergeb. Oceanic plate (denser) is subducted beneath the continental crusti. Overlying mantle is melted, magma rises, and some solidifies in crustThese notes represent a detailed interpretation of the professor’s lecture. GradeBuddy is best used as a supplement to your own notes, not as a substitute.ii. This creates volcanoes and mountain belts1. Example: Ring of Fire around the Pacific Oceana. Spreading in East Pacific Rise (spreading center)b. Oceanic plates subducted on both sidesc. Andes Mountains in South America: subduction beneath continental formsIV. Continent-Continent Convergencea. Definition: two continental plates collideb. Example: Eastern United Statesi. Oceanic to continental convergent boundaries brings other continental plate closer and closer until it becomes a continent to continent boundary, forming terrain/mountain beltsc. Continental collision causes a wide zone of deformationi. Continental plates are buoyant so subduction ends  few volcanoesii. Beneath collision in mountain belts, there is a very thick crust1. Example: Tibetan plateau/Himalayan Mountains and lowlands in IndiaV. Transform Boundarya. Definition: plates moving horizontally past each other adjacent to divergent boundaryi. Strike slip faults along transform boundariesii. Transforms link spreading segments in mid ocean ridgeiii. Example: San Andreas faultb. Fracture zone – when both plates are moving next to each other in the same direction VI. Plate Movementa. What moves the plates?i. Largest force = slab pull – the subducting plate pulls the other down with itii. Other forces = convection currents in the mantleb. Relative rates of plate movementi. Mid Atlantic Ridge – 3cm per yearii. East Asia/Papua New Guinea – 9 or more cm per yeariii. Differences in plate motionc. Direct measurements of plate motioni. Can be taken with very sensitive GPS unitsVII. Geometry of plate boundariesa. Transform boundaries link other types of plate boundaries, like 2 spreading centersb. North America and Pacific Plate – transform boundary (Queen Charlotte Fault)i. As the boundary bends as you travel north, it eventually becomes convergentVIII. Earth’s Magnetic Fielda. Liquid outer core contains convection currents because the inner core is spinning; since both are iron rich materials, this creates magnetic fieldsb. Magnetic crystals in solid rock point toward the magnetic north at the time the rock was formed and cooledc. Earth’s magnetic field has changed overtime i. Today: south pole to north poleii. Reversed: north pole to south poled. Magnetic reversals are recorded by a mid ocean ridge during seafloor spreading  mirror images of stripes centered around spreading centersi. Measurements of this led to observations and questions about plate tectonicsIX. Evidence for plate tectonicsa. Age of sea floor i. Youngest nearest to spreading center, oldest farther awayb. Thickness of sediment away from spreading center/ridgei. Thinnest closer to the spreading center, thicker farther awayX. Formation of linear islands and seamount chainsa. Observation: form in linesb. Reason: plate is moving over a hot spotc. Oldest island is farthest away from hot spot XI. Why is South America lopsided?a. Cross section showing both South American coasts reveals:i. Spreading center in Mid-Atlantic Ridgeii. Eastern South America is a passive marginiii. Western South America has deformation and a subduction zoneb. Combination of these processes and rates creates a “lopsided”