lecture 5: mineral assemblage and paragenesis mineral ... · not all minerals present in a...

Not all minerals present in a (metamorphic) rock are necessarily in equilibrium

an assemblage of minerals in mutual equilibrium is called a mineral paragenesis and a rock or thin-section can contain multiple equi assemblages or parageneses as relicts, overgrowths, inclusions, partial replacements etc. etc.

�15

Lecture 5: Mineral assemblage and paragenesis

Indicators of equilibrium:• minerals in direct contact, contacts are sharp and with correct crystal faces• mutual inclusions of A in B and B in A• ideal inter-mineral angles• …

Surface tension (or interfacial energy) generates a characteristic contact angle between minerals, also called the dihedral angle:

�16

Mineral assemblage and paragenesis

When Eint(A) = Eint(B), the angle is 120˚

When Eint(A) > Eint(B), the angle is less 120˚ so as to minimize the A-A interface length

figures from Winter (chapter 23)

Surface tension (or interfacial energy) generates a characteristic contact angle between minerals, also called the dihedral angle

�17


c.

plag

plag

cpx

figure from Winter (chapter 23)

cpx

Assemblage and paragenesis

from Bucher and Frey 2002

two assemblages =two parageneses

one assemblage =two parageneses

one assemblage = one paragenesis

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Not all minerals present in a (metamorphic) rock are necessarily in equilibrium

an assemblage of minerals in mutual equilibrium is called a mineral paragenesis and a rock or thin-section can contain multiple equi assemblages or parageneses as relicts, overgrowths, inclusions, partial replacements etc. etc.

This is a very important concept, because the succession of mineral paragene-ses provides information on the history of the rock and its metamorphic path

preservation of multiple generations of equilibrium mineral assemblages results from lower reaction rates resulting from a combination of lower temperatures, solid state reactions, lack of a fluid phase etc.

Igneous petrology focuses on the mineral paragenesis, metamorphic petrology on the history of the rock and its metamorphic path

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prograde replacement retrograde replacement

with precursor minerals preserved: information on rock’s history �20

Mineral assemblage and paragenesis: an example

�21

chl ep ccpl q ru

chl ep pl ccdol q ru

amp chlpl q ilm

ampchl

ep pl

q ilm

chl ep ccpl q ilm

ampchl epgt q ilm

amp chl eppl gt q ilm

ampchl

ep ilm q

amp chl ccep gt q ilm

amp plgt ilm q

amp pl gtcpx ilm q

amp chl plgt q ilm

melt pl amp gt cpx

ilm q

900Temperature (oC)

Pres

sure

(kb

ar)

10001

3

5

7

9

500 600 700 800

2

4

6

8

Approxim

ate depth (km)

5

15

25

10

20

30

300 400

Sample 512256greenschist Nuuluk

amp pl gtcpx ilm q

amp pl gt cpx ilm

amp plgt ilm

chl ampdol plq ru amp pl

gt q ilm

chlamppl gtq ilm

chlamppl gt ilm

chl amppl q ilm

chl amppl dol gt

q ilm

chl amppl dolq ilm

chl plgt q

ilm dol

amp pl gtdol q ilm

amp chl plgt dol q ru

chl pl gtdol q ilm ru

melt amppl gt cpx

q ilm

meltamp plgt cpx

ilm

melt pl gtcpx ilm

melt plcpx ilm

melt gtcpx ilm

Pres

sure

(kb

ar)

Ti-Na-Ca-Fe-Mg-Al-Si-H-Osaturated in H2O-CO2 fluid

1

3

5

7

9

2

4

6

8

Approxim

ate depth (km)

5

15

25

10

20

30chlampdol

mgs pl ru q

chlampdolmgsab

q ru

chl ampdol abq ru

chl dolpl q ru

chl dolab q ru

chl dol pl qilm

chl dolpl q ru

ilm

Sample 512184greenstone Nuuluk

amp pl gtcpx ilm q

melt plgt cpxilm q melt

pl gtcpxilm

melt gt cpx q ilm

meltpl

cpx ilm

meltgt cpxilm

chl dolpl q ru

chl ep dolpl q ru

chl dolpl ilm q

dol chl amp plilm q

chl amppl ilm q

chl ep dolpl ilm q

dol chlamp pl qgt ilm

chl dolpl gtilm q

chl amppl gt ilm q

amp plgt ilm q

dol plgt ilm

q

dol amppl gt ilm q

dol amp pl gt cpxilm q

pl gt cpxilm q

Pres

sure

(kb

ar)

1

3

5

7

9

2

4

6

8

Approxim

ate depth (km)

5

15

25

10

20

30Sample 510866greenschist Nuuluk

ep

chl ep ccpl q ru


amp chlpl q ilm

ampchl

ep pl

q ilm

chl ep ccpl q ilm

ampchl epgt q ilm


ampchl

ep ilm q


amp plgt ilm q

amp pl gtcpx ilm q

amp chl plgt q ilm

melt pl amp gt cpx

ilm q

900Temperature (oC)

Pres

sure

(kb

ar)

10001

3

5

7

9

500 600 700 800

2

4

6

8

Approxim

ate depth (km)

5

15

25

10

20

30

300 400


amp pl gtcpx ilm q

amp pl gt cpx ilm

amp plgt ilm


gt q ilm

chlamppl gtq ilm

chlamppl gt ilm

chl amppl q ilm

chl amppl dol gt

q ilm

chl amppl dolq ilm

chl plgt q

ilm dol

amp pl gtdol q ilm



melt amppl gt cpx

q ilm

meltamp plgt cpx

ilm

melt pl gtcpx ilm

melt plcpx ilm

melt gtcpx ilm

Pres

sure

(kb

ar)


1

3

5

7

9

2

4

6

8

Approxim

ate depth (km)

5

15

25

10

20

30chlampdol

mgs pl ru q

chlampdolmgsab

q ru

chl ampdol abq ru

chl dolpl q ru

chl dolab q ru

chl dol pl qilm

chl dolpl q ru

ilm


amp pl gtcpx ilm q


pl gtcpxilm

melt gt cpx q ilm

meltpl

cpx ilm

meltgt cpxilm

chl dolpl q ru

chl ep dolpl q ru

chl dolpl ilm q

dol chl amp plilm q

chl amppl ilm q

chl ep dolpl ilm q


chl dolpl gtilm q

chl amppl gt ilm q

amp plgt ilm q

dol plgt ilm

q

dol amppl gt ilm q


pl gt cpxilm q

Pres

sure

(kb

ar)

1

3

5

7

9

2

4

6

8

Approxim

ate depth (km)

5

15

25

10

20


ep

ep

�22


�23


�24


�25


�26

chl ep ccpl q ru


amp chlpl q ilm

ampchl

ep pl

q ilm

chl ep ccpl q ilm

ampchl epgt q ilm


ampchl

ep ilm q


amp plgt ilm q

amp pl gtcpx ilm q

amp chl plgt q ilm

melt pl amp gt cpx

ilm q

900Temperature (oC)

Pres

sure

(kb

ar)

10001

3

5

7

9

500 600 700 800

2

4

6

8

Approxim

ate depth (km)

5

15

25

10

20

30

300 400


amp pl gtcpx ilm q

amp pl gt cpx ilm

amp plgt ilm


gt q ilm

chlamppl gtq ilm

chlamppl gt ilm

chl amppl q ilm

chl amppl dol gt

q ilm

chl amppl dolq ilm

chl plgt q

ilm dol

amp pl gtdol q ilm



melt amppl gt cpx

q ilm

meltamp plgt cpx

ilm

melt pl gtcpx ilm

melt plcpx ilm

melt gtcpx ilm

Pres

sure

(kb

ar)


1

3

5

7

9

2

4

6

8

Approxim

ate depth (km)

5

15

25

10

20

30chlampdol

mgs pl ru q

chlampdolmgsab

q ru

chl ampdol abq ru

chl dolpl q ru

chl dolab q ru

chl dol pl qilm

chl dolpl q ru

ilm


amp pl gtcpx ilm q


pl gtcpxilm

melt gt cpx q ilm

meltpl

cpx ilm

meltgt cpxilm

chl dolpl q ru

chl ep dolpl q ru

chl dolpl ilm q

dol chl amp plilm q

chl amppl ilm q

chl ep dolpl ilm q


chl dolpl gtilm q

chl amppl gt ilm q

amp plgt ilm q

dol plgt ilm

q

dol amppl gt ilm q


pl gt cpxilm q

Pres

sure

(kb

ar)

1

3

5

7

9

2

4

6

8

Approxim

ate depth (km)

5

15

25

10

20


ep

chl ep ccpl q ru


amp chlpl q ilm

ampchl

ep pl

q ilm

chl ep ccpl q ilm

ampchl epgt q ilm


ampchl

ep ilm q


amp plgt ilm q

amp pl gtcpx ilm q

amp chl plgt q ilm

melt pl amp gt cpx

ilm q

900Temperature (oC)

Pres

sure

(kb

ar)

10001

3

5

7

9

500 600 700 800

2

4

6

8

Approxim

ate depth (km)

5

15

25

10

20

30

300 400


amp pl gtcpx ilm q

amp pl gt cpx ilm

amp plgt ilm


gt q ilm

chlamppl gtq ilm

chlamppl gt ilm

chl amppl q ilm

chl amppl dol gt

q ilm

chl amppl dolq ilm

chl plgt q

ilm dol

amp pl gtdol q ilm



melt amppl gt cpx

q ilm

meltamp plgt cpx

ilm

melt pl gtcpx ilm

melt plcpx ilm

melt gtcpx ilm

Pres

sure

(kb

ar)


1

3

5

7

9

2

4

6

8

Approxim

ate depth (km)

5

15

25

10

20

30chlampdol

mgs pl ru q

chlampdolmgsab

q ru

chl ampdol abq ru

chl dolpl q ru

chl dolab q ru

chl dol pl qilm

chl dolpl q ru

ilm


amp pl gtcpx ilm q


pl gtcpxilm

melt gt cpx q ilm

meltpl

cpx ilm

meltgt cpxilm

chl dolpl q ru

chl ep dolpl q ru

chl dolpl ilm q

dol chl amp plilm q

chl amppl ilm q

chl ep dolpl ilm q


chl dolpl gtilm q

chl amppl gt ilm q

amp plgt ilm q

dol plgt ilm

q

dol amppl gt ilm q


pl gt cpxilm q

Pres

sure

(kb

ar)

1

3

5

7

9

2

4

6

8

Approxim

ate depth (km)

5

15

25

10

20


ep

�27


�28


�29

chl ep ccpl q ru


amp chlpl q ilm

ampchl

ep pl

q ilm

chl ep ccpl q ilm

ampchl epgt q ilm


ampchl

ep ilm q


amp plgt ilm q

amp pl gtcpx ilm q

amp chl plgt q ilm

melt pl amp gt cpx

ilm q

900Temperature (oC)

Pres

sure

(kb

ar)

10001

3

5

7

9

500 600 700 800

2

4

6

8

Approxim

ate depth (km)

5

15

25

10

20

30

300 400


amp pl gtcpx ilm q

amp pl gt cpx ilm

amp plgt ilm


gt q ilm

chlamppl gtq ilm

chlamppl gt ilm

chl amppl q ilm

chl amppl dol gt

q ilm

chl amppl dolq ilm

chl plgt q

ilm dol

amp pl gtdol q ilm



melt amppl gt cpx

q ilm

meltamp plgt cpx

ilm

melt pl gtcpx ilm

melt plcpx ilm

melt gtcpx ilm

Pres

sure

(kb

ar)


1

3

5

7

9

2

4

6

8

Approxim

ate depth (km)

5

15

25

10

20

30chlampdol

mgs pl ru q

chlampdolmgsab

q ru

chl ampdol abq ru

chl dolpl q ru

chl dolab q ru

chl dol pl qilm

chl dolpl q ru

ilm


amp pl gtcpx ilm q


pl gtcpxilm

melt gt cpx q ilm

meltpl

cpx ilm

meltgt cpxilm

chl dolpl q ru

chl ep dolpl q ru

chl dolpl ilm q

dol chl amp plilm q

chl amppl ilm q

chl ep dolpl ilm q


chl dolpl gtilm q

chl amppl gt ilm q

amp plgt ilm q

dol plgt ilm

q

dol amppl gt ilm q


pl gt cpxilm q

Pres

sure

(kb

ar)

1

3

5

7

9

2

4

6

8

Approxim

ate depth (km)

5

15

25

10

20


ep

chl ep ccpl q ru


amp chlpl q ilm

ampchl

ep pl

q ilm

chl ep ccpl q ilm

ampchl epgt q ilm


ampchl

ep ilm q


amp plgt ilm q

amp pl gtcpx ilm q

amp chl plgt q ilm

melt pl amp gt cpx

ilm q

900Temperature (oC)

Pres

sure

(kb

ar)

10001

3

5

7

9

500 600 700 800

2

4

6

8

Approxim

ate depth (km)

5

15

25

10

20

30

300 400


amp pl gtcpx ilm q

amp pl gt cpx ilm

amp plgt ilm


gt q ilm

chlamppl gtq ilm

chlamppl gt ilm

chl amppl q ilm

chl amppl dol gt

q ilm

chl amppl dolq ilm

chl plgt q

ilm dol

amp pl gtdol q ilm



melt amppl gt cpx

q ilm

meltamp plgt cpx

ilm

melt pl gtcpx ilm

melt plcpx ilm

melt gtcpx ilm

Pres

sure

(kb

ar)


1

3

5

7

9

2

4

6

8

Approxim

ate depth (km)

5

15

25

10

20

30chlampdol

mgs pl ru q

chlampdolmgsab

q ru

chl ampdol abq ru

chl dolpl q ru

chl dolab q ru

chl dol pl qilm

chl dolpl q ru

ilm


amp pl gtcpx ilm q


pl gtcpxilm

melt gt cpx q ilm

meltpl

cpx ilm

meltgt cpxilm

chl dolpl q ru

chl ep dolpl q ru

chl dolpl ilm q

dol chl amp plilm q

chl amppl ilm q

chl ep dolpl ilm q


chl dolpl gtilm q

chl amppl gt ilm q

amp plgt ilm q

dol plgt ilm

q

dol amppl gt ilm q


pl gt cpxilm q

Pres

sure

(kb

ar)

1

3

5

7

9

2

4

6

8

Approxim

ate depth (km)

5

15

25

10

20


ep

ep

�30


Sequence of metamorphic mineral parageneses in one thin-section:

1. Present as inclusions in garnet: amphibole + rutile + epidote

2. Main mineral stage: garnet + amphibole + ilmenite + quartz + plagioclase

3. Replacement at grain edges: amphibole to biotite

4. Locally on plagioclase grains: plagioclase going to albite

A metamorphic P-T path reconstructed from prograde, peak and retrograde mineral parageneses, all of which are subsets of the rock mineral assemblage

�31

chl ep ccpl q ru


amp chlpl q ilm

ampchl

ep pl

q ilm

chl ep ccpl q ilm

ampchl epgt q ilm


ampchl

ep ilm q


amp plgt ilm q

amp pl gtcpx ilm q

amp chl plgt q ilm

melt pl amp gt cpx

ilm q

900Temperature (oC)

Pres

sure

(kb

ar)

10001

3

5

7

9

500 600 700 800

2

4

6

8

Approxim

ate depth (km)

5

15

25

10

20

30

300 400


amp pl gtcpx ilm q

amp pl gt cpx ilm

amp plgt ilm


gt q ilm

chlamppl gtq ilm

chlamppl gt ilm

chl amppl q ilm

chl amppl dol gt

q ilm

chl amppl dolq ilm

chl plgt q

ilm dol

amp pl gtdol q ilm



melt amppl gt cpx

q ilm

meltamp plgt cpx

ilm

melt pl gtcpx ilm

melt plcpx ilm

melt gtcpx ilm

Pres

sure

(kb

ar)


1

3

5

7

9

2

4

6

8

Approxim

ate depth (km)

5

15

25

10

20

30chlampdol

mgs pl ru q

chlampdolmgsab

q ru

chl ampdol abq ru

chl dolpl q ru

chl dolab q ru

chl dol pl qilm

chl dolpl q ru

ilm


amp pl gtcpx ilm q


pl gtcpxilm

melt gt cpx q ilm

meltpl

cpx ilm

meltgt cpxilm

chl dolpl q ru

chl ep dolpl q ru

chl dolpl ilm q

dol chl amp plilm q

chl amppl ilm q

chl ep dolpl ilm q


chl dolpl gtilm q

chl amppl gt ilm q

amp plgt ilm q

dol plgt ilm

q

dol amppl gt ilm q


pl gt cpxilm q

Pres

sure

(kb

ar)

1

3

5

7

9

2

4

6

8

Approxim

ate depth (km)

5

15

25

10

20


ep

chl ep ccpl q ru


amp chlpl q ilm

ampchl

ep pl

q ilm

chl ep ccpl q ilm

ampchl epgt q ilm


ampchl

ep ilm q


amp plgt ilm q

amp pl gtcpx ilm q

amp chl plgt q ilm

melt pl amp gt cpx

ilm q

900Temperature (oC)

Pres

sure

(kb

ar)

10001

3

5

7

9

500 600 700 800

2

4

6

8

Approxim

ate depth (km)

5

15

25

10

20

30

300 400


amp pl gtcpx ilm q

amp pl gt cpx ilm

amp plgt ilm


gt q ilm

chlamppl gtq ilm

chlamppl gt ilm

chl amppl q ilm

chl amppl dol gt

q ilm

chl amppl dolq ilm

chl plgt q

ilm dol

amp pl gtdol q ilm



melt amppl gt cpx

q ilm

meltamp plgt cpx

ilm

melt pl gtcpx ilm

melt plcpx ilm

melt gtcpx ilm

Pres

sure

(kb

ar)


1

3

5

7

9

2

4

6

8

Approxim

ate depth (km)

5

15

25

10

20

30chlampdol

mgs pl ru q

chlampdolmgsab

q ru

chl ampdol abq ru

chl dolpl q ru

chl dolab q ru

chl dol pl qilm

chl dolpl q ru

ilm


amp pl gtcpx ilm q


pl gtcpxilm

melt gt cpx q ilm

meltpl

cpx ilm

meltgt cpxilm

chl dolpl q ru

chl ep dolpl q ru

chl dolpl ilm q

dol chl amp plilm q

chl amppl ilm q

chl ep dolpl ilm q


chl dolpl gtilm q

chl amppl gt ilm q

amp plgt ilm q

dol plgt ilm

q

dol amppl gt ilm q


pl gt cpxilm q

Pres

sure

(kb

ar)

1

3

5

7

9

2

4

6

8

Approxim

ate depth (km)

5

15

25

10

20


ep

ep

�32

lecture 5: mineral assemblage and paragenesis mineral ... · not all minerals present in a...

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