Metamorphism

Metamorphism

1. Types

   • Regional
   • High pressure
   • Contact
   • Seafloor
   • Burial
   • Shock

2. Causes

   • Increases in pressure
   • Increase in temperature
   • Reactions with chemical components

3. Two major textural classes

   • foliated
     • a pattern of parallel cleavage planes resulting from a preferred orientation of crystals
     • textures
       • slaty cleavage
         • parallel arrangement of fine-grained metamorphic minerals, consisted of close spaced planar surfaces along which rocks split into thin, tabular slabs when hit with a hammer
       • schistocity
         • characterisitc of coarser-grained rocks, parallel arrangement of platy minerals such as micas
       • gneissic
         • dark and light silicate minerals have separated, giving the rock a banded appearance
   • non foliated
     • granular, characterised by coarse or fine interlocking grains, little or no preferred orientation

4. Most likely settings

   • thermal
     • rock intruded by magma body
   • regional
     • subjected to direct pressures and high temperatures, greatest volume of metamorphic rock
   • hydrothermal
     • involves chemical alterations that occur as hot ion-rich water circulates through fractures in rock

5. Effect of degree on texture/mineral composition

   • low grade
     • more compact, more dense --> hard
   • more extreme
     • minerals recrystallize to form large crystals (tiny mica --> larger mica crystals