EM Ch 1

• Solid Earth materials


  Described by their chemical, mineral, and rock composition
• All the atoms in solid Earth materials are held together in fixed positions by forces called chemical bonds
• Properties of minerals

  • Solid
  • Naturally occurring
  • Formed by inorganic processes
  • Have a specific chemical composition
  • Have a long-range, geometric arrangement of constituent atoms or ions
• Some solid materials form by both organic and inorganic processes (example: CaCO3)
• Chemical compositions of minerals may vary within well-defined limits because minerals incorporate impurities, have atoms missing, or otherwise vary from their ideal composition
• Each mineral has a specific chemical composition which can be expressed by a chemical formula
• Minerals crystallize in geometric patterns so that the same pattern is repeated throughout the mineral
• The basic pattern of atoms (motif) is repeated systematically to produce the entire geometric design
• Crystal structure

  The long range pattern of atoms characteristic of a mineral species
• Crystalline materials


  Materials that have geometric crystal structures
• Amorphous materials


  Materials that do not have long-range crystal structure
• Properties used to define minerals


  • Naturally occurring
  • Solid
  • Lack one of the properties
  • Over 3500 minerals discovered
  • Atoms combine to form minerals
• Rocks


  Aggregates of mineral crystals and/or mineraloids
• Types of rocks

  • Monomineralic
  • Polymineralic
• Mineral composition is a defining property of a rock alongside texture and structures
• Minerals combine to form rocks
• Earth materials occur anywhere within the Earth
• Compositional layers of the Earth

  • Crust
  • Mantle
  • Core
• Crust


  • About 5-80km thick and occupies 1% of the Earth's volume
• Mantle


  • Has a radius of ~2885km and occupies ~83% of Earth's volume
• Core


  • Has a radius of ~3480km and occupies ~16% of Earth's volume
• Mechanical layers of the Earth

  • Lithosphere
  • Asthenosphere
  • Mesosphere
  • Outer core
  • Inner core

  
• Lithosphere


  Strong and rigid; have an average depth of ~100km; includes crust and upper part of the mantle
• Asthenosphere


  Weak and plastic; have depths of 100-660km; includes a transition zone from ~400-660km
• Mesosphere


  Lower mantle; depth of ~660-2900km
• Outer core


  Depth of ~2900-5150km
• Inner core

  Below 5150km to the center of the Earth
• The outermost layer of the geosphere is extremely thin and separated from the mantle by the Mohorovicic discontinuity (Moho)

  
• Types of crust

  • Oceanic
  • Continental

  
• Oceanic crust


  • Composed of dark-colored, mafic rocks enriched in oxides of Mg, Fe, and Ca
  • 5-7km thick; reaches 18km in some oceanic islands
  • Less buoyant than continental crust
  • Occupies areas of lower elevation on the Earth's surface (ocean basins)
  • Composed of pyroxene and Ca-plagioclase
  • Relatively young; no oceanic crust older than 180 MY

  
• Continental crust


  • Have much more variable composition that oceanic crust
  • Rocks are light-colored, low density, felsic, and rich in quartz, K- and Na-feldspar
  • Average thickness is 30km; reaches 80km in areas of high elevation
  • More buoyant that oceanic crust
  • Occupies areas of higher elevation on the Earth's surface (continents)
  • Oldest found is 4.03 BYO at the Northwest Territories of Canada

  
• Comparison of oceanic and continental crust characteristics

  • Composition
  • Density
  • Thickness
  • Elevation
  • Age

  
• Mantle


  • Thick (~2900km)
  • Constitutes ~83% of the Earth's volume
  • Very rich in MgO (30-40%) and, to a lesser extent, FeO
  • Dominated by olivine and pyroxene
• Lithosphere


  • Uppermost part of mantle + crust
  • Strong enough to rupture due to stress
  • Site of most earthquakes and broken into plates

  
• Asthenosphere


  • Occurs within the upper mantle at depths of ~100-250km
  • More plastic flow slowly, rather than rupturing, when subjected to stress
  • Extends to the base of the LVZ at depth of 660km

  
• Transition zone


  • Between depths of ~410-660km
  • Mineral transformations responsible for changes in seismic velocity at 410km and 660km depths

  
• Major minerals in the lower mantle

  • Perovskite
  • Periclase
  • Magnesiowustite
  • Stishovite
  • Ilmenite
  • Ferrite
• Lower mantle (mesosphere)


  • Extends from depth of 660km to ~2900km
  • Can be related to the formation of deep mantle plumes within the lower mantle
• Gutenburg discontinuity


  • Occurs at the 2900km depth
  • P-wave velocity decrease, S-wave terminated
  • Boundary between core and mantle

  
• Outer core


  • Liquid (inferred because S-waves are not transmitted here)
  • Have a density of ~10-12 g/cm3
  • Circulation of molten Fe is responsible for the production of the magnetic field