Definition of a Metamorphic Rock - A rock that results from the alterations of existing rocks due to high pressure/or temperature.
 

Factors controlling the existence of Metamorphic Rocks

1. Composition of parent rock

2. Temperature. Minerals that are stable at higher temps tend to be less dense

3. Pressure - Confining (static); Directed (dynamic) compressive, shearing

Products of pressure

Foliation is the parallel alignment of minerals

Different variations of foliation -

a) Slaty (slaty cleavage),

b) Phyllite (sheen appearance)

c) Schistose,

d) Gneissic,

4. Effects of Fluids

        2Mg₂SiO₄ + 2H₂O (Olivine) Mg₃Si₂O₅(OH)₄ (Serpentine) + MgO carried away
          Water reacts with olivine to produce serpentine with Mg oxide removed by water

5. Time
 
 
 

Classification of Metamorphic Rock

1) 1^st Step - Is rock foliated? -

  a) Yes, type of foliation;

  b) No, Composition

Non-foliated Metamorphic rocks- Marble (Limestone), Quartzites (sandstone), Hornfels (Shale), Hornfels (Basalt), Greenstone, Anthracite, chlorite, epidote (mica, garnet, cordiante), Metaconglomerate

Foliated metamorphic rocks- Slate, Phyllite, Schist, Gneiss, Amphibole, Migmatite
 

Types of Metamorphism

Most important/prevalent types of metamorphism

1. Contact

2. Dynamic

1. Contact

2. Cataclastic - grinding activities as observed in faults...could result  in Dynamic Mylomite

3. Hydrothermal - associated midocean ridge

4. Burial -

5. Regional

6. Pyrometamorphism - lightning

7. Dynamothermal - convey plate border

8. Shock out - meteorite
 

Contact (Thermal) Metamorphism - High temp is the dominant factor; directed pressure is not involved so rock is not foliated.

-With contact metamorphism, the area affected is small; 1-40mm wide.

-shale hornfels Limestone marble or dolomite dolomitic marble are products of contact metamorphism.

-Contact Aureole (metamorphic halow) - area where contact is made with surrounding rock.
 

Regional Metamorphism

Majority of metamorphic rocks are regional or dynamothermal-high temperature, preserve (directed and confining) due to depth.

Depending on temperature and pressure, rock will be different even if they all had same type of parent rock. e.g. Slate phyllite schist gneiss migmatite

Index minerals High grade

Green schist Amphibole Pyroxene

Chlorite

Muscovite

Biotite

Garnet

Staurolite

Kyanite

Sillimanite
 

Isogrades - lines connecting places where index minerals first appear

Isograde sequence may differ from metamorphic belt to another depending on pressure and temperature.
 

Metamorphic facies and Grade

Defined by mineral assemblage Intensity of metamorphism
 
 
 

Plate tectonics and Metamorphism

'Dry' metamorphism

'Wet' metamorphism....Here water transports ions between grains in rocks

Metasomatism - Water brings ions from outside rock and add to rock during metamorphism altering chemical and mineral composition.

Hydrothermal Rocks (Veins) - Water passes through cracks or pore spaces in rocks and precipitates minerals on the walls of cracks and in pore spaces
 
 
 

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