Plate Tectonics

Wegener came up with them Pangea = "all earth"

1. Seismology
   1. Volcanoes

      Forms extrusive igneous rock

      1. Shield

         Hawaii. Formed from successive lava flows. Typically basaltic, as it is very fluid.

      2. Strato

         More conical than shield. Granite. Solid material comes out, not as fluid.

      3. Cinder Cone

         Small, weak, hillish.

   2. Hot Spots

      Explains Hawaii. Hot magma pushes up on plate, breaks through in spots.

   3. Earthquakes

      Release of stored energy between plates Has a focus, can be 0-700km below surface Top Shell is elastic Epicenter = Spot above the focus Near earthquake, shallow waves are picked up, away deep waves are picked up. Seismic tomography = triangulation

      1. Seismic Waves
         1. Surface Waves
         2. Body Waves
         3. P-Waves

            Primary Waves Result from compression of material, compression waves

         4. S-Waves

            Shear waves Only transfer through solids

2. Structure of Earth
   1. Crust

      Continental crust is thicker, less dense, and older the oceanic crust

      1. Rocks

         Made of silicates and feldspars

         1. Igneous

            Formed by colling and solidification of magma.

            1. Intrusive

               Formed by magma solidifing below Earth's surface Granite

            2. Extrusive

               Formed by magma solidifing at surface, such as lava Basalt

         2. Sedimentary

            Created by lithification, the conversion of loose sediments into thick cohesive layed deposits. Settle on the bottom of the ocean.

            1. Sandstone

               Created from rough grain

            2. Mudstone

               Created from finer grain

            3. Shale

               Fine, layed mudstone

            4. Limestone

               Biologically created

         3. Metamorphic

            Created by high pressure and temperature but NOT melting. Limestone -> Marble, Shale -> Slate

   2. Moho Boundary

      7 km below ocean floor

   3. Mantle

      P-waves travel much faster than at crust, slow velocity increase as you go deeper. Relatively uniform, made from silicates. Only 1% needs to be melted for data to make sense

   4. Outercore

      Roughly 2900km deep S-waves cease to transmit Metallic fluid. Creates magnetic field

   5. Innercore

      5150km deep Solid, increase in P-wave speed compared to outer core. Expanding, releasing heat into the outercore making it convect.

   6. Continents
      1. Craton

         Stable interior that is extremely old

      2. Terranes

         Other pieces of crust added to Craton

3. Sea-Floor Spreading

   Floor is youngest at the ridges as fresh magma builds there.

4. Continental Drift

   Continents drift... Reconstructed from magnetic info, various linkages on edges of continents, life, etc.

   1. Lithosphere

      Crust and upper upper mantle. Portion that the plates are in.

   2. Astenosphere

      Fluid, flows and deforms

5. Plates and Plate Boundaries

   Lithosphere consists of around 20 plates, periods of stasis and movement

   1. Divergent Margins

      Lithosphere being pulled apart. Location of mid-atlantic ridges. Create rift valleys on continents Heavy geothermal energy, deep sea hot springs. Iceland sits on midatlantic ridge, will split eventually.

   2. Convergent Margins

      Plates being forced together. Creates deep sea trenches

      1. Ocean to Continent Convergence

         One plate subducts, volcanos and earthquakes are created Oceanic plate is converted into fresh magma.

      2. Ocean to Ocean Convergence

         Builds island arcs

      3. Continent to Continent Convergence

         Alps, Himalayas Too bouyant to subduct

   3. Transform Margins

      Sliding plates Earthquakes LA will eventually be north of San Franciso San Andreas fault

6. Driving the Plates

   Plate tectonics is how energy leaves the interior of the Earth The heat comes from radioactive decay and leftover heat from the formation of the earth. Radio active heat has decreased by a power of 5 since the earth's creation. Circulation cells occure in the mantle. There are more forces acting on the plates than just mantle drag, but some heat/density operations also.

7. The Rock Cycle
   1. Weathering and Erosion

      Freezing water and rain cracks and erodes

   2. Sediment Accumulation

      Because of the pressure and water currents at extreme depth, they can become sedimentary rocks

   3. Uplift

      Creates mountains

   4. Metamorphism

      Magma gets put into colder places.

8. History

   Slowly losing some heat, plates were more active at other times.

   1. Wilson Cycle

      Supercontinent is formed every 500 million years