ERSC 3P21 Metamorphic Petrology I 22/08/2011
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ERSC 3P21 - Brock University Greg Finn
ERSC 3P21Metamorphic
Petrology
ERSC 3P21 - Brock University Greg Finn
Metamorphism_____________, __________ and __________ adjustments in solid rocks in response to ________ and __________ conditions which have been imposed due to changes in __________ (_) and ________ (_)
ERSC 3P21 - Brock University Greg Finn
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 _________
ERSC 3P21 Metamorphic Petrology I 22/08/2011
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ERSC 3P21 - Brock University Greg Finn
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.
ERSC 3P21 - Brock University Greg Finn
Copyright 2002 G.C. Finn
garnet
hornblende
plagioclase
Foliation
ERSC 3P21 - Brock University Greg Finn
___________ 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
ERSC 3P21 Metamorphic Petrology I 22/08/2011
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ERSC 3P21 - Brock University Greg Finn
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
ERSC 3P21 - Brock University Greg Finn
___________ 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
ERSC 3P21 - Brock University Greg Finn
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
ERSC 3P21 Metamorphic Petrology I 22/08/2011
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ERSC 3P21 - Brock University Greg Finn
Prograde vs RetrogradeTemperature
Pres
sure
Peak ofMetamorphism
ERSC 3P21 - Brock University Greg Finn
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
ERSC 3P21 - Brock University Greg Finn
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
ERSC 3P21 Metamorphic Petrology I 22/08/2011
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ERSC 3P21 - Brock University Greg Finn
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
ERSC 3P21 - Brock University Greg Finn
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 ___________
ERSC 3P21 - Brock University Greg Finn
Metamorphic Grade
• Metamorphism is the ______________ ________________________________________________________________
• How Big do the changes have to be to cause metamorphism?
• Answer is dependent on:–––
ERSC 3P21 Metamorphic Petrology I 22/08/2011
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ERSC 3P21 - Brock University Greg Finn
Metamorphic Grade• Grade is used to signify the _________
_______________________, which corresponds approximately to a progressive increase in temperature
• Four Divisions of Grade– ________________– ________________– ________________– ________________
ERSC 3P21 - Brock University Greg Finn
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
ERSC 3P21 - Brock University Greg Finn
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)
ERSC 3P21 Metamorphic Petrology I 22/08/2011
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ERSC 3P21 - Brock University Greg Finn
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)
MEDIUMGRADE
HIGHGRADE
LOWGRADE
VERYLOW
GRADE
Look at thisboundary
ERSC 3P21 - Brock University Greg Finn
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
ERSC 3P21 - Brock University Greg Finn
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)
MEDIUMGRADE
HIGHGRADE
LOWGRADE
VERYLOW
GRADEor+ab+q
Liquid
mu + qor+Al2SiO5+H2O
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