.
Week 9: March 13-17

Types of granites based on geochemistry and origin
  • I-type: generated by melting of igneous rock
  • S-type: generated by melting of sedimentary rock
  • A-type: "anorogenic" granites
  • M-type: fractional crystallization of mantle-derived magmas
Igneous rocks of various tectonic settings - a review of concepts from previous lectures with some new information
  • Convergent boundaries
    • ocean-ocean - predominantly basalt and basaltic andesite formed by melting of the mantle wedge (with fractional crystallization). More silicic varieties in more mature arcs with an increasing role for AFC processes
    • ocean-continent - more silicic varieties dominate. AFC process is important
    • continent-continent - anatexis of crustal rock
  • Divergent boundaries
    • mid-ocean ridges - dominated by basalt formed by pressure-release melting of the mantle
    • continental rifts - more alkaline varieties formed by pressure release melting but with lower degrees of partial melting as well as melting of more "enriched mantle"
  • Hot spots
    • oceanic - dominated by basalts formed by pressure release melting from plumes
    • continental - more silicic varieties become important because of AFC processes.
"Unusual" magmatism 
  • Flood basalt magmatism (large igneosu provinces)
  • carbonatites
  • kimberlites
  • komatiites
Review of causes of variety in igneous rocks
  • Variations in the source rock of magmas
  • Variable degree of partial melting
  • Contamination and assimilation
  • Magma mixing
  • Magmatic differentiation
    • liquid immiscibility
    • volatile transport
    • fractional crystallization
      • by crystal settling
      • flow differentiation
      • crystal growth on magma chamber margins
      • "filter pressing"
  • summary figure: GIF image or PDF file

Petrology homepage | Saint Louis University | Earth & Atmospheric Sciences