Transcript Metamorphism - Overview

Metamorphism - Overview
 Metamorphism literally means to “change form.”
 Metamorphism causes a change in the rock’s mineral
composition and a change in the rock’s texture.
What causes the changes? (i.e. Change Agents)
(1) Heat/Temperature
(2) Pressure
(3) Hot Chemical Fluids (e.g. Water)
 These changes occur at various depths beneath Earth’s
surface, from 2 - 3 km depth down deep to the crust mantle boundary (MOHO).
Metamorphism - Overview
 All three types of rocks (i.e. igneous, sedimentary, and
metamorphic) can be metamorphosed.
• Example: Granite (Igneous) To Gneiss (Met.)
• Example: Sandstone (Sedimentary) To Quartzite (Met.)
• Example: Slate (Metamorphic) To Schist (Met.)
 Metamorphism DOES NOT involve a melt and there IS
NO recrystallization of minerals from such a melt.
•It is the hot chemical fluids that serve to dissolve away
previous minerals and serve as the medium for the
crystallization of NEW MINERALS.
Metamorphism - Overview
 Metamorphism can cause CHANGES in;
1) Texture: Two types of textures:
A) Foliated and B) Non-foliated.
2) Volume: The volume of a metamorphic rock is less than
the volume of the parent rock. This is due to the
metamorphic agent called pressure.
3) Chemical Change: New minerals are often the result.
These minerals are different from the minerals that were
present in the parent rock.
Note: Hot chemical fluids are often essential as a
transport medium for the movement of ions and the
formation of new minerals.
Metamorphism - Overview
 Three Metamorphic agents cause rocks to change;
1) increased heat
2) increased pressure
3) chemically active fluids
 Metamorphism most often occurs in one of two geologic
settings;
1) during mountain building (regional metamorphism)
2) surrounding masses of molten rock (contact
. metamorphism.)
Metamorphism - Overview
 Metamorphism of rocks can vary in degree from a rock
that is slightly changed, low grade metamorphism (Shale
to Slate), to a rock that undergoes great change, high
grade metamorphism (Granite to Gneiss).
1) Low-Grade Metamorphism
 Rocks are subjected to small changes in temperatures and
pressures which result in slight changes to the rock.
 Example: Shale changes to form slate.
Metamorphism - Overview
 Metamorphism of rocks can vary in degree from a rock
that is slightly changed, low grade metamorphism (Shale
to Slate), to a rock that undergoes great change, high
grade metamorphism (Granite to Gneiss).
2) High-Grade Metamorphism
 Rocks are subjected to extreme temperatures and
pressures (close to that at which rocks melt) which result
in great changes to the rock.
 Example: Granite changes to form Gneiss.