Chapter 5 - Earth Structure and Plate Tectonics

I.      Seismic Waves
        A. Body (penetrating) waves
            1. Primary
            2. Secondary
        B. Surface (outer crustal) waves
            1. Rayleigh
            2. Love

II.     Divisions of Inner Space
        A. Main Discontinuities in Earth
            1. Mohorovicic (30 km)
            2. Gutenberg (2900 km)
        B. Earth's Core
            1. Detected by P and S waves shadow zones
            2. Average density 10.7 g cm3
            3. Composed mainly of Fe and Ni
            4. Radius: 3500 km
            5. Inner core (solid) and outer core (liquid)
        C. Earth's Mantle
            1. Stony composition (4.5 g cm3)
            2. Layers:  Upper, transition (250 km thick), lower (above core)
            3. Upper mantle features
                a. low velocity zone
                b. asthenosphere (plastic layer)
        D. Earth's Crust
            1. Oceanic crust (basaltic; 3.0 g cm3)
            2. Continental crust (granitic; 2.7 g cm3)
                a. thickest crust (35km)
                b. floats due to isostasy

III.    Crustal Structures
        A. Faults
            1. Normal (gravity)
            2. Reverse (also thrust)
            3. Lateral (right to left)
        B. Folds
            1. Anticlines and synclines
            2. Domes and basins
            3. Monoclines

IV.     Plate Tectonics
        A. Older concept of Continental Drift
            1. Ancient super continents - later fragmented
                a. Gondwanaland (Suess' idea, 1890's)
                b. Pangea (Wegener's idea, 1915)
            2. Evidence cited for drifting
                a. geologic and geographic fit
                b. climatic evidence (tillites, coal etc.)
                c. fossil distribution (Glossopteris, Mesosaurus)
        B.  Discoveries about Paleomagnetism (1950's - 1960's)
            1. Magnetic poles susceptible to switching N-S
            2. Rocks preserve weak remnant magnetism from time of formation
                a. thermoremanent (Curie point = 578 degrees C)
                b. depositional-remanent
            3.  Polar wandering: Only explanation for paleomagnetic shifts if
                continental drift is zero
        C. Basic concept of modern Plate Tectonics
            1. Integration of ideas: Unifying concept
                a. continental drift
                b. sea-floor data
                c. paleomagnetic data
            2. Mechanism of movement: Plates slide on asthenosphere
            3. Plate boundaries
                a. divergent (sea floor spreading, rifting)
                b. convergent (trenches, folded mountains)
                c. shear (great lateral or transform faults)
            4. Tectonics of convergent boundaries
                a. suture zones (folded mountains)
                b. subduction zones (melange and blue schist’s)
            5. Driving mechanism: Competing theories
                a. mantle convection-induced drag on the lithosphere
                b. "ridge-push" - "slab-pull"
            6. Effect of mantle's thermal plumes
                a. doming of overlying plate
                b. three-armed crustal rifts
            7. Test of Plate Tectonics Theory
                a. sea-floor studies of Hess (1960's)
                b. paleomagnetism of sea floor (Vine 1963)
                c. Paleomagnetism of crust (Cox, 1963)
                d. sediment cores from drilling ships, Glomar Challenger and
                JOIDES Resolution (1969-date)
                e. laser measurements of crustal motion from space
            8. Earthquake (seismic evidence)
                a. Benioff zones (deep focus)
                b. Ridge zones (shallow focus)
            9. Gravity evidence: Lower gravity over divergent boundary due to thin
                crust
            10. Hot spots:  Island chains and seamounts
            11. Alien terrains (far-traveled microcontinents)
                a. suspect terrains
                b. allochthonous terrains

V.      Plate Tectonics and Ore Deposits
        A. Plate boundaries
            1. mobile belts
            2. spreading centers
        B. Intra-plate sites: Sea floors

VI.     Plate Tectonics and Fossil Evolution
        A. Effect of Supercontinents
            1. Wide, stable environments
            2. Broad distribution of fauna and flora (provinces)
            3. Ease of migration and fewer barriers
            4. Bast, unbroken ocean (e.g. Panthalassa)
        B. Effect of Continental dispersion
            1. Fragmentation of environments
            2. Barriers: Mountains built, seas opened
            3. Inhibition of migration
            4. Climatic change
            5. Latitudinal change for continents

VII.    Exotic Terrane:  video and discussion