Lecture 7: Plate Tectonics

Geological Cycles

  • Provide the physical foundation to support life on Earth

Rock cycle

  • Heating, melting, cooling, breaking, reassembling of rocks and minerals
  • Dominated by surface processes
  • Internal and external

Tectonic cycle

  • Processes related to the movement of large fragments of lithosphere
  • Dominated by internal processes


Advantages of Geological cycles

  1. Determine soil chemistry and replenish nutrients
  2. Drive formation of mineral resources and fossil fuels
  3. Influence development of landscapes and mountain ranges
  4. Contribute to changes in atmospheric chemistry
  5. Determine location, size and shape of ocean basins
  6. Control oceanic/atmospheric circulation and the distribution of climatic zones
  7. Influence the distribution of vegetation and ecosystems.

The Rock Cycle

Igneous rock

  • Magma - Molten (liquid) rock + gases + crystals
  • Lava - Magma that reaches the surface
  • Igneous rock forms when magma cools
  • Intrusive (Plutonic) Rock
  • Magma cools and crystallizes slowly below Earth's surface
  • Example \rightarrow granite
  • Extrusive (Volcanic) Rock
  • Magma ejected from a volcano, cools and solidifies quickly
  • Example \rightarrow basalt


Sedimentary rock

  • Sediment - Particles of rock, transported by wind, water, ice, or gravity
  • Sedimentary rock forms in the surface environment
  • Lithification - Formation of rock through the processes of compaction and cementation
  • Example
  • Fossils - Preserved remains of long ­dead organisms


Metamorphic rock

  • Pre-existing rock, modified as a result of exposure to great heat and/or pressure
  • Temperature and pressure high enough to reshape crystals
  • Changes their appearance, physical properties and chemistry


The Earth is Different

  • It's not homogeneous
  • Has internal layering defined by differences in physical properties and composition


Methods used to learn about the inside of Earth

  • Direct study of rocks
  • Drill holes
  • Laval
  • Surface rocks
  • Foreign rocks (Xenolith)
  • Indirect methods
  • Astronomical and orbital measurements
  • Planetary mass and density
  • Meteorite analogy
  • Planetary composition
  • Gravity and magnetism measurements
  • Refraction of seismic waves


Earthquakes

  • They're a release of built­-up seismic energy
  • Occurs as a result of build­up and release of strain energy in blocks of rock subjected to tectonic forces
  • Ground Shaking
  • Fault is the rock fracture along with relative movement occurs
  • Focus is the initial point of rupture along a fault
  • Focal depth influences earthquake impacts
  • Epicentre is point on the surface directly above the focus
  • Seismic waves are refracted if they travel more quickly through some layers than others
  • Those waves are blocked by the outer core because they can't travel through liquids
  • Travel paths of seismic waves are the single most important source of info about Earth's interior


Earth's layers

  • The Mantle
  • Made of dense rock (not as dense as the core)
  • Asthenosphere
  • "weak zone"
  • Near melting point
  • The Core
  • Made of Fe-­Nil metal
  • Inner Core \rightarrow Solid
  • Outer Core \rightarrow Liquid
  • The Crust
  • Oceanic Crust \rightarrow Basalt, dense, thin
  • Continental Crust \rightarrow Granite, less dense, thick
  • Crust + Top of Mantle = Lithosphere



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