ERSC 3P21 Metamorphic I HO.ppt - Brock University · Metamorphic Rocks • To recognize a metamorphic rock and distinguish it from an igneous or sedimentary rock two criteria are

ERSC 3P21 Metamorphic Petrology I 22/08/2011

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ERSC 3P21 - Brock University Greg Finn

ERSC 3P21Metamorphic

Petrology


Metamorphism_____________, __________ and __________ adjustments in solid rocks in response to ________ and __________ conditions which have been imposed due to changes in __________ (_) and ________ (_)


Metamorphism• The conditions of metamorphism differ from

the conditions under which the rocks in question ___________– e.g. basalt solidifies on the Earth’s surface at T=

~1,200°C and 1 atm pressure• Original rock is referred to as the _________


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Metamorphic Rocks

• To recognize a metamorphic rock and distinguish it from an igneous or sedimentary rock two criteria are used:

Metamorphic ___________________– the group of minerals that form in a rock as

a result of metamorphism, and;Metamorphic ___________________

– parallel surfaces or layers that develop in a rock as a result of metamorphism.


Copyright 2002 G.C. Finn

garnet

hornblende

plagioclase

Foliation


___________ Metamorphism• Metamorphism resulting from the

_________ _______ in temperature and pressure,– i.e. by burial of a rock within the Earth

• ____________ gradient 20-30°C/km• ____________ gradient – 3.5 kbar/km

• The progressive change from ______ to _____ to ______ to _____ to ______ is an example of prograde metamorphism


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Prograde Metamorphism

• In general, Prograde Metamorphism is characterized by a series of _________ ___________, which release water

Mineral(OH)2 ===> Mineral + H2O

Muscovite + Quartz ===> Al2SiO5 + Kspar + H2OMuscovite ===> Kspar + Corundum + H2O


___________ Metamorphism• Metamorphism can also take place as a

result of __________ temperature and pressure conditions

• This type is referred to as Retrograde Metamorphism

• For retrograde metamorphism to occur water must be ___________________, to hydrate the minerals, and thus it takes much longer to occur than prograde metamorphism


Retrograde Metamorphism• Retrograde metamorphism is usually

associated with a __________ _______ (hot water)

• Retrograde metamorphism does not happen automatically when a high-grade rock is uplifted to the Earth’s surface

• ________________ under cold dry conditions is a very, very slow process, taking billions of years to complete


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Prograde vs RetrogradeTemperature

Pres

sure

Peak ofMetamorphism


Limits of MetamorphismLower limit• Marks the boundary between

metamorphism and ____________• Lower T = ____ – ______°C• Excludes any ___________ changes• Generally defined as the first

appearance of a mineral which does not occur in ______ _____________ rocks


Limits of MetamorphismUpper Limit• Metamorphism generally considered to

end when large scale _____ of _______ character are produced

• Upper T, will vary over a wide pressure range, with excess water, depending on the _____ ____________ of the rock– In Mudstones _____°C– In mafic lithologies ________°C


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Assemblage vs Association• Within an individual thin section of a

metamorphic rock _______ __________ and ________ _____________ are observed

• Mineral Association– Consists of all minerals _________ in a single thin

section– Minerals may or may not be in ____________ with

each other


Assemblage vs Association• Within an individual thin section of a

metamorphic rock Mineral Assemblagesand Mineral Associations are observed

• Mineral Assemblage (_____________)– Consists of those minerals which grew at the

same time, i.e. in ____________.– They exhibit a stable or meta-stable coexistence

during the metamorphic event of interest.– These minerals are in _________ with each other.– A given mineral assemblage forms under _______

P and T ___________


Metamorphic Grade

• Metamorphism is the ______________ ________________________________________________________________

• How Big do the changes have to be to cause metamorphism?

• Answer is dependent on:–––


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Metamorphic Grade• Grade is used to signify the _________

_______________________, which corresponds approximately to a progressive increase in temperature

• Four Divisions of Grade– ________________– ________________– ________________– ________________


Metamorphic Grade• Boundaries between the four divisions

of grade are marked by significant changes in the _______ __________ in common rocks

• Changes correspond to specific reactions that occur within the lithology


Metamorphic GradeCalculatedGeothermalGradient

Watersaturatedgranitesolidus

Diagenesis

100

2

200 300 400 500 600 700 800 900 1000

14

12

10

8

6

4 10

20

30

40

Temperature (C)

Pres

sure

(kba

r)

Dep

th (k

m)


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Diagenesis

100

2

200 300 400 500 600 700 800 900 1000

14

12

10

8

6

4 10

20

30

40

Temperature (C)

Pres

sure

(kba

r)

Dep

th (k

m)

MEDIUMGRADE

HIGHGRADE

LOWGRADE

VERYLOW

GRADE

Look at thisboundary


Metamorphic GradeBoundary between medium and high grade• Based on two reactions1. At P < 3.0 kbars

Musc + qtz ===> or + Al2SiO5 +H2OT = 580°C, P = 1 kbar, T = 600°C, P = 3 kbar

2. At P > 3.0 kbarsAb + qtz + or ===> Granitic Liquid

– Corresponds to the water saturated granite solidusT = 660°C, P = 3 kbar, T < 600°C, P = 6 kbar




Diagenesis

100

2

200 300 400 500 600 700 800 900 1000

14

12

10

8

6

4 10

20

30

40

Temperature (C)

Pres

sure

(kba

r)

Dep

th (k

m)

MEDIUMGRADE

HIGHGRADE

LOWGRADE

VERYLOW

GRADEor+ab+q

Liquid

mu + qor+Al2SiO5+H2O

ERSC 3P21 Metamorphic I HO.ppt - Brock University · Metamorphic Rocks • To recognize a metamorphic rock and distinguish it from an igneous or sedimentary rock two criteria are

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