Studied by 9 people
Metamorphic rocks
Rocks that have undergone metamorphism
Metamorphism
the change undergone by an existing rock (ign, sed, or met) in the solid state, to another rock
Solid
During metamorphism, the rock must remain essentially in this state
Contact or thermal metamorphism
Hydrothermal metamorphism
Regional metamorphism
Metamorphic settings
Contact or thermal metamorphism
driven by a rise in temperature within the host rock
Hydrothermal metamorphism
chemical alterations from hot, ion-rich water
Regional metamorphism
occurs during mountain building
Regional metamorphism
What type of metamorphic settings produces the greatest volume of metamorphic rocks
Prograde metamorphism
results from increasing temperature and/or pressure conditions over time
Retrograde metamorphism
results from decreasing temperature and/or pressure so that lower temperature/pressure mineral assemblages develop that overprint earlier peak temperature/pressure mineral assemblages
Volatiles
they serve as catalysts in driving retrograde metamorphic reactions as without them, retrograde metamorphic conditions are difficult to attain because previously occurring prograde metamorphism has already depleted the rock in volatile components
Heat
The most important agent of metamorphism
Heat from magma
Geothermal gradient
2 sources of heat
Pressure
An agent of metamorphism, it increases with depth
Confining pressure
Differential stress
2 types of pressure
Confining pressure
it applies forces equally in all directions
Differential stress
Rocks may also be subjected in this type of pressure which is unequal in different directions
Chemically active fluids
Agent of metamorphism, mainly water with other volatile components. They enhance migration of ions, and aid in recrystallization of existing minerals
Water trapped in pore spaces of the original rock
Water released during dehydration of minerals, such as amphibole or mica
Water from magmatic bodies (hydrothermal fluids)
Sources of fluids
Protolith
the parent rock of metamorphic rocks, the original, unmetamorphosed rock from which a given metamorphic rock is formed
Foliated
Non-foliated
2 main classification of metamorphic rocks
Shale, mudstone
Protolith of Slate
Shale, slate, basalt, or granite
Protolith of Schist
Shale, schist, granite, sandstone, and other rock types
Protolith of Gneiss
Sandstone
Protolith of Quartzite
Limestone, dolomite
Protolith of Marble
Bituminous coal
Protolith of Anthracite coal
Contact or Thermal metamorphism
Hydrothermal metamorphism
Regional metamorphism
Burial metamorphism
Metamorphism along Fault Zones
Impact metamorphism
Types of metamorphism
Contact or thermal metamorphism
Occurs due to a rise in temperature when magma invades a host rock
Aureole
It is a zone of alteration that forms in the rock surrounding the magma during contact metamorphism
0-60 km
Contact metamorphism takes place in low pressure and at these depths
Non-foliated; fine-grained
type of metamorphic rocks produced by contact metamorphism
Hydrothermal metamorphism
Chemical alteration at high temperatures and moderate pressures by hot-ion rich fluids that circulate through fissures and cracks. Common in basaltic rocks
Mid-ocean ridge system
This is where hydrothermal metamorphism commonly occur
Regional metamorphism
Takes place at considerable depths over an extensive area under high pressure and is associated with the process of mountain building
5-20 km sometimes more than 30 km
The depth where regional metamorphism takes place
Burial metamorphism
Associated with very thick sedimentary strata. Required depth varies from one location to another depending on the prevailing geothermal gradient.
Metamorphism along Fault Zones
Occurs at depth and high temperatures. Pre-existing minerals deform by ductile flow. “Slickensides”
Shock or Impact Metamorphism
Occurs when high speed projectiles called meteorites strike Earth’s surface
impactites
Products of impact metamorphism
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