Metamorphism

Meta- means ___________.
Morph means ___________.
Metamorphic rocks are rocks which have had their form changed.
Parent Rock is the original, unaltered, unchanged rock.
Parent rocks can be igneous, sedimentary or metamorphic rocks.
Metamorphism occurs due to changes in temperature, pressure or chemistry.

Temperature and Metamorphism

Changes in temperature will result in changes to the minerals or structure of the rock.
The temperature of metamorphism has two limits:
Lower limit of metamorphism - 200°C
Upper limit varies between 700-1200°C
Heat sources for metamorphism:

Pressure and Metamorphism

Changes in pressure will change the crystalline structure of minerals and the structure of the rock.
Confining Pressure - pressure applied equally in all directions.
Directed Pressure - pressure applied in a single direction.

Chemical Changes and Metamorphism

Hydrothermal fluid, hot water plus other chemicals and gases can add or remove chemicals from the rock, thus changing the overall chemistry of the rock.

Types of Metamorphism

Contact Metamorphism
Regional Metamorphism

Cataclastic Metamorphism
Burial Metamorphism
Shock Metamorphism

Classification of Metamorphic Rocks

Metamorphic rocks are classified based on the temperature and pressure of maximum metamorphism.
Determined by the minerals present in the rock (mineral stability fields)
Difficult to do in this classroom.
Texture and Composition system.

Texture

Two catagories:
Foliated Texture - foliation is a distinct planar character which results from directed pressure.
- minerals show a preferred orientation or alignment
1) Slaty cleavage - very fine foliation
2) Phyllitic foliation - very fine foliation
2) Schistosity - medium scale foliation
3) Gneissic banding - alternating bands of light and dark colored minerals
Non-Foliated Texture - no preferred orientation of the minerals in the rock

Foliated Metamorphic Rock Types

Slate - Low grade (low T and P), slaty cleavage, minerals are too small to see, Parent Rock = shale, mudstone.
Phyllite - Low grade, slaty cleavage, slightly larger crystals than slate - still too small to see, appearance shows a slight sheen, Parent Rock = shale, mudstone.
Schist - Medium grade (moderate T and P), schistosity, platy minerals dominate (micas), Parent Rock = fine grained igneous rocks, slate, phyllite
Gneiss - High grade (high T and P), gneissic banding, Parent Rock = schist, plutonic igneous rocks

Non-Foliated Metamorphic Rock Types

Metaconglomerate - Parent Rock = conglomerate, pebbles have been flattened
Quartzite - fine to medium interlocking quartz grains, Parent Rock = sandstone.
Marble - fine to medium interlocking calcite crystals, Parent Rock = limestone.
Anthracite Coal - Low grade (if T is too high, the coal turns to graphite), Parent Rock = bituminous coal.

Porphyroblasts

Larger crystals set in a finer matrix.

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