Metamorphic Rocks Metamorphic Rocks

Metamorphic Rocks Metamorphic Rocks Metamorphism:Metamorphism:

The transition of one rock into another in the solid The transition of one rock into another in the solid state under conditions unlike those under which it state under conditions unlike those under which it formedformed

Metamorphic rocks are produced from:Metamorphic rocks are produced from:Igneous rocksIgneous rocksSedimentary rocksSedimentary rocksOther metamorphic rocksOther metamorphic rocks

Agents of MetamorphismAgents of Metamorphism

HeatHeat-- The most important agentThe most important agent Recrystallization results in new, stable Recrystallization results in new, stable

mineralsminerals Two sources of heatTwo sources of heat

Contact metamorphismContact metamorphism – heat from magma – heat from magma Regional Metamorphism Regional Metamorphism - increase in - increase in

temperature with depth due to the temperature with depth due to the geothermal gradientgeothermal gradient

Agents of MetamorphismAgents of Metamorphism

PressurePressure Increases with depthIncreases with depth Confining pressureConfining pressure applies forces equally in applies forces equally in

all directionsall directions Rocks may also be subjected to Rocks may also be subjected to differential differential

stressstress which is unequal in different which is unequal in different directions and causes directions and causes deformationdeformation

Agents of MetamorphismAgents of Metamorphism PressurePressure

Types of MetamorphismTypes of Metamorphism

Contact Contact metamorphismmetamorphism

From Understanding Earth, Press and Siever. Freeman.

Types of MetamorphismTypes of Metamorphism

Regional metamorphismRegional metamorphism

Types of MetamorphismTypes of Metamorphism

Regional metamorphismRegional metamorphism

More More UpliftUplift

Types of MetamorphismTypes of MetamorphismRegional metamorphismRegional metamorphism

From Understanding Earth, Press and Siever. Freeman.

Metamorphic TexturesMetamorphic Textures

FoliationFoliation - any planar arrangement of features - any planar arrangement of features within a rockwithin a rock

FoliationFoliation can form in various ways: can form in various ways: Rotation of platy and/or elongated mineralsRotation of platy and/or elongated minerals Recrystallization of minerals in the direction Recrystallization of minerals in the direction

of preferred orientationof preferred orientation Changing the shape of equidimensional Changing the shape of equidimensional

grains into elongated shapes that are alignegrains into elongated shapes that are alignedd

Metamorphic TexturesMetamorphic TexturesFoliationFoliation can form in various ways: can form in various ways:

Metamorphic TexturesMetamorphic Textures Foliated texturesFoliated textures

Slaty cleavageSlaty cleavage Closely spaced planar surfaces along which Closely spaced planar surfaces along which

rocks splitrocks split

Metamorphic TexturesMetamorphic Textures Foliated texturesFoliated textures

SchistositySchistosity Platy minerals are discernible with the Platy minerals are discernible with the

unaided eye and exhibit a planar or layered unaided eye and exhibit a planar or layered structurestructure

Rocks having this texture are referred to as Rocks having this texture are referred to as schistschist

Metamorphic TexturesMetamorphic Textures Foliated texturesFoliated textures

GneissosityGneissosity During higher grades of metamorphism, ion During higher grades of metamorphism, ion

migration results in the segregation of migration results in the segregation of minerals into layersminerals into layers

Gneissic rocks exhibit a distinctive banded Gneissic rocks exhibit a distinctive banded appearanceappearance

Metamorphic TexturesMetamorphic Textures

Metamorphic rocks that lack foliation are Metamorphic rocks that lack foliation are referred to as referred to as non-foliatednon-foliated Develop in environments where Develop in environments where

deformation is minimal deformation is minimal And/or composed of minerals that And/or composed of minerals that

exhibit equidimensional crystalsexhibit equidimensional crystals General name is General name is granofelsgranofels

Metamorphic Rocks Metamorphic Rocks Foliated Metamorphic Rocks Foliated Metamorphic Rocks

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Slate: compact, very fine-grained, metamorphic rock with a well-developed cleavage. Freshly cleaved surfaces are dull

Phyllite: a rock with a schistosity in which very fine phyllosilicates (sericite/phengite and/or chlorite), although rarely coarse enough to see unaided, impart a silky sheen to the foliation surface. Phyllites with both a foliation and lineation are very common.

Metamorphic Rocks Metamorphic Rocks Foliated Metamorphic Rocks Foliated Metamorphic Rocks

Schist: a metamorphic rock exhibiting a schistosity. By this definition schist is a broad term, and slates and phyllites are also types of schists. In common usage, schists are restricted to those metamorphic rocks in which the foliated minerals are coarse enough to see easily in hand specimen.

Metamorphic Rocks Metamorphic Rocks Foliated Foliated

Metamorphic Metamorphic Rocks Rocks

Gneiss: a metamorphic rock displaying gneissose structure. Gneisses are typically layered (also called banded), generally with alternating felsic and darker mineral layers. Gneisses may also be lineated, but must also show segregations of felsic-mineral-rich and dark-mineral-rich concentrations.

Metamorphic Rocks Metamorphic Rocks Specific Metamorphic Rock Types Specific Metamorphic Rock Types

Marble:Marble: a metamorphic rock composed a metamorphic rock composed predominantly of calcite or dolomite. The protolith predominantly of calcite or dolomite. The protolith is typically limestone or dolostone.is typically limestone or dolostone.

Metamorphic Rocks Metamorphic Rocks Specific Metamorphic Rock Types Specific Metamorphic Rock Types

Quartzite:Quartzite: a metamorphic rock composed a metamorphic rock composed predominantly of quartz. The protolith is typically predominantly of quartz. The protolith is typically sandstone. sandstone.

Metamorphic Rocks Metamorphic Rocks Greenschist/Greenstone:Greenschist/Greenstone: a low-grade metamorphic a low-grade metamorphic

rock that typically contains chlorite, actinolite, rock that typically contains chlorite, actinolite, epidote, and plagioclase. Such a rock is called epidote, and plagioclase. Such a rock is called greenschist if foliated, and greenstone if not. The greenschist if foliated, and greenstone if not. The parent is either a mafic igneous rock or graywacke.parent is either a mafic igneous rock or graywacke.

Metamorphic Rocks Metamorphic Rocks Specific Metamorphic Rock Types Specific Metamorphic Rock Types

Amphibolite:Amphibolite: a metamorphic rock dominated by a metamorphic rock dominated by hornblende + plagioclase. Amphibolites may be hornblende + plagioclase. Amphibolites may be foliated or non-foliated. The parent is either a foliated or non-foliated. The parent is either a mafic igneous rock or graywacke.mafic igneous rock or graywacke.