The Theory of Plate Tectonics Chapter 11

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The Earth Inside and Out

Inner core = mostly iron nickel with some other heavy elements (5000 degrees Celsius and solid) Outer Core= Same elements and temperature but lower pressure makes it liquid (thermal plumes) Mantle= mostly silicone and oxygen (SiO2 and SiO4) with some iron and magnesium. Divided into upper mantle (lithosphere + asthenosphere) Solid, but due to extreme temperature rocks behaves with fluid properties, like hot glass, “plasticity”

The Earth Inside and Out Crust= mainly oxygen and silicon, with magnesium and iron. Lithosphere includes upper most rigid part of the mantle and the crust Scientists distinguish between upper mantle and the crust because of certain elemental composition changes Mantle contains more iron and magnesium, making the rocks denser and heavier. Felsic (continental crust), Mafic (oceanic crusts), Ultra Mafic (mostly asthenosphere)

Rock Cycle

Isostatic Equilibrium Isostatic Equilibrium: Definition: the balance between the weight of the crust and the buoyancy provided by the mantle. Oceanic crust (denser, colder, deposition of sediment and volcanic activity) Continental crust (warmer, less dense, + erosion) Reason why mountains have “Roots”

Alfred Wegner and Continental Drift Pangaea + Panthalassa Laurasia + Gondwanaland

New Technology and Seafloor Knowledge Using an Echo-Sounder, the German Meteor expedition mapped the contours and depths of the South Atlantic 1940, Hugo Benioff, seismology and Ring of Fire. Mid-ocean Ridges, trenches, and Rift valleys.

New Technology and Seafloor Knowledge

The Creation and Destruction of Seafloor Mid-Ocean Ridge = Seafloor being created at Rift Valleys Trenches = Subduction (Seafloor Destruction) Average age of oceanic crusts is estimated to be between million years Occurs at a rate similar to the growth of finger nails

The Creation and Destruction of Seafloor

Evidence of Seafloor Spreading 3 Forms of Evidence for Seafloor Spreading: Sediment layers are thin or absent at ridges and grow thicker as you move away, which makes sense since the oldest seafloor would have accumulated more sediment over time. 2 nd Radiometric Dating: based on known decay rates of unstable elements in rocks, absolute dating is possible. Scientists found seafloor to be significantly younger than continental rock, as well as younger rock the closer you are to ridges. Magnetometer data (measures polar orientation), symmetrical pattern in polar orientation of magnetism of seafloor basalt rock.

1963 Fred Vines and Drummond Matthews

The Unifying Theory: Plate Tectonics (Seafloor Spreading and Cont Drift Combined) Earth’s lithosphere is composed of plates (some only oceanic crust, some continental, some both) They move by cm per year, powered by convection (maybe), as well as slab pull (from subduction zones) and slab push (from elevated rift) As plates move they form convergent, divergent, and transform boundaries. Divergent = seafloor spreading (rift valleys) Volcanic activity at divergent boundary may build mountains (possibly Iceland)

Divergent Boundary

The Unifying Theory: Plate Tectonics (Seafloor Spreading and Cont Drift Combined) Convergent = subduction (seafloor destruction at Trenches) One plate is subducted (sinks beneath) the other Can result in volcanic island arc (like Japan) along oceanic to oceanic plate boundary Volcanic mountain range produced along continental to oceanic plate boundary (Ring of fire, Andes mountains ect) Continental to continental convergent boundary = crust folding and mountain formation (Himalayas) 2drA7dE3cZyj4npEWdmma6UVsL3x6WfvkwBIGZwOnP3P1cz1d5c4FCXVxVGfWE4 hfByn2861Z8kreQQ 2drA7dE3cZyj4npEWdmma6UVsL3x6WfvkwBIGZwOnP3P1cz1d5c4FCXVxVGfWE4 hfByn2861Z8kreQQ

Oceanic - Oceanic

Oceanic - Continental

Continental - Continental

Transform AKA Fault Boundary San Andreas Fault Plates slide past each other Boundary between Pacific and North American Plate Basin and Range formation: NHa4s NHa4s

San Andreas Fault Boundary

Hot Spots Small melting areas within mantle, where thermal plumes cause magma to push up intensely eventually breaking through the crust Can occur at plate boundaries but further from the edge (Yellowstone national park) Hot spots do not move with plates since the originate from asthenosphere, resulting in rows of volcanic formations (Hawaiian Islands)

Hot Spots

Plate Movement Driving Forces Convection (questionable) Seafloor Spreading Plates pushing into, or past each other Slab Pull

New Explanation for Seafloor Spreading and Plate Tectonics 21st Century Earth Dynamics Part 1: st Century Earth Dynamics Part2: lNVIJCuipbVjdJH88TlpFg7TQOYdqhFfW9ffAZ0llMmwPZ_VuDg2dm68T5V OW99vw-BtEcFsUyh4BKxxwVVMw lNVIJCuipbVjdJH88TlpFg7TQOYdqhFfW9ffAZ0llMmwPZ_VuDg2dm68T5V OW99vw-BtEcFsUyh4BKxxwVVMw