Mineralogy and Petrology

Major problems

• Metamorphism: textures and processes
  • Texture: foliation
  • Processes
    • Lateral pressure
    • Heat (magma intrusions or hot fluid)
    • Regional versus contact
  • Main idea
    • Chemical interactions
    • Elevated temperature and pressure
    • Lead to different mineral assemblage
  • Underlying issue
    • Tectonics and mountain building
    • Classification/relation of granite and gneiss
• Origin of granite
  • Various models suggested
    • “Lava lakes” from Earth’s beginning
    • Migmatite: percolation into texture
      • Involves some amount of water
      • High heat and pressure (link to metamorphism)
    • Igneous: slowly cooling magma
      • Unclear how well quartz fits with this model
  • Order of mineral crystallization was unknown
• Origin of magmas
  • Differentiation of single magmas
    • Question of how to differentiate precipitates
    • Partial precipitation and continued migration
    • Crystal settling to separate them from magma (changes composition)
  • Multiple origins
    • Mixing of more than one magma bodies
    • Attribute different magmas to different depth
      • Near surface
      • Deep, dense magmas

Broader perspective

• Real need for experimental work to examine textures, mineral sequences, etc.
• Field relations for temporal sequences, relation of metamorphic foliation and regional stress

Key Innovations

• Petrographic Microscope
  • Developed by Nichol by 1829
  • Came into wide use by later 1860s-70s
  • Revolutionized study of igneous and metamorphic rocks
• Chemical thermodynamics
  • Provide chemical background to study of geological materials
  • Gibbs (1874-78) was the landmark publication
• Geophysical Laboratory (Washington DC)
  • Founded in 1905 under the direction of Arthur Day
  • Center for experimental investigations of rocks and minerals