Introduction to

PetrologyFrancis 2014

Introductory Petrology EPSC-212BDon Francis: Room: F.D.A. 316, donald.francis@mcgill.caDocuments: www.eps.mcgill.ca/~c212

1. Igneous:

- Elemental abundances, Sun, meteorites, mantle, crust Jan 6

- Units, minerals, phase equilibria Jan 8

- Test on rock forming minerals, review of minerals Jan 9/10 - Phase diagrams for simple mafic systems Jan 13

- Mafic magmas, mantle, and ocean crust Jan 15

- Magmatic textures Jan 16/17

- Variation diagrams, calc-alkaline versus tholeiitic suites Jan 20

- Mafic Intrusions and cumulate rocks Jan 22

- Volcanic rocks Jan 23/24

- Phase diagrams for simple felsic systems Jan 27

- Granitoids and continental crust Jan 29

- Plutonic rocks Jan 30/31

Introductory Petrology EPSC-212B

2. Sedimentary:

- Weathering and erosion Feb 3

- Transport and deposition Feb 5

- Igneous test (10 marks), sedimentary structures and textures Feb 6/7

- Siliciclastics Feb 10

- Bio-chemical precipitates I: carbonates Feb 12

- Siliciclastic rocks Feb 13/14

- Bio-chemical precipitates II: dolostones, evaporites, chert, etc. Feb 17

- Depositional environments Feb 19

- Limestones, dolomites, cherts, etc Feb 20/21

- Mid-Term Test (10 marks) Feb 26

- Sedimentary test (10 marks) Feb 27/28

- Cementation and diagenesis Mar 10

- Sedimentary basins and sequence stratigraphy Mar 12

Introductory Petrology EPSC-212B

3. Metamorphic:

- Metamorphic minerals and textures Mar 13/14

- Reactions: solid - solid, dehydration and decarbonation Mar 17

- Reactions: mixed volatile, net transfer, exchange Mar 19

- Meta-pelites Mar 20/21

- Meta-pelites Mar 24

- Meta-basites Mar 26

- Meta-basites and meta-carbonates Mar 27/28

- Meta-carbonates Mar 31

- P-T regimes, geothermometry, and geobarometry Apr 2

- Lab review Apr 3/4

- Buffering Apr 7

- Metamorphism and tectonics Apr 9

- Final lab test Apr 10/11

Introductory Petrology EPSC-212B

Marking:

2 Lab Spotting Tests (20 marks)

Final Lab Exam (20 marks)

Mid-Term Exam (10 marks)

Final Theory Exam (50 marks)

Lectures:

Mon & Weds 11:30 - 12:30 am Room: FDA 315

Lab:

Thurs 2:30 - 5:30 pm Room: FDA 315

or

Fri 2:30 - 5:30 pm Room: FDA 315

Francis, Intro. Petrology EPSC 212, 2014

Texts/References on Reserve in PSE Library and/or my Office Winter, J.D.; 2001: An Introduction to Igneous and

Metamorphic Petrology. Prentice Hall, QE461.W735 200

Francis, Intro. Petrology EPSC 212, 2014

Boggs, S.; 2012: Principles of Sedimentology and Stratigraphy. Prentice Hall, New Jersey. QE471 B66.

T.A.s: Ryan Libby - FDA 346Gregor Lucic - FDA 130AThomas Maguire - FDA 349Volker Moeller - FDA 346

Philpotts, A.R., and Ague, J.J.; 2009: Principles of Igneous and Metamorphic Petrology, Cambridge University Press.

Required Component of Course Outlines

Integrity:

McGill University values academic integrity.  Therefore all students must understand the meaning and consequences of cheating, plagiarism and other academic offences under the Code of Student Conduct and Disciplinary Procedures (seewww.mcgill.ca/students/srr/honest/  for more information).

Language:

In accord with McGill University’s Charter of Students’ Rights, students in this course have the right to submit in English or in French any written work that is to be graded.

Francis, Intro. Petrology EPSC 212, 2013

Igneous Petrology

The study of rocks that form by the:

crystallization of a cooling melt (“liquid”) or magma

Fundamental challenge : to understand high temperature crystal-liquid processes by studying cold solid rocks

Solid(xyl) Liquid(liq)

Cxyli / Cliq

i = Ki

Elemental partitioning between coexisting solid and liquid

followed by the physical separation of solid(s) and liquid 0livine

glass

K

constanttemperature

Diversity of igneous rocks reflects the action of

crystal – liquid fractionation

processes at high temperature

(Fe/Mg)oliv / (Fe/Mg)liq ~ 0.3

Natural silicate melts are complex systems with many components and thus melt over a range of temperatures. Because of the high aspect ratios of plagioclase, basalt becomes rigid in the range of 30 to 40% solidification. Note how a cube of solid basalt retains its shape to 70% melting, even as the partial melt drains out of the bottom.

basalt cube - % melted60% 70% 75%

Two Kinds of Igneous Rocks:

Basalt/gabbro: dark or mafic rocks dominated by Fe-Mg silicates, such as olivine, and pyroxenes.

Constitute the oceanic crust.

Granitoids: light or felsic rocks dominated by feldspar and quartz .

Constitute the continental crust.

Black/Dark

White/Light

Basalt

Granite

Mantle - Ocean & Continent crust

Oceanic crust - MORB basalt - p

Continental crust - granite - e

ContinentalCrust

Oceanic Crust

Composition of the Sun and the Cosmic Abundances of the Elements: 

As the Sun constitutes 99.98 wt.% of the solar system, the chemical composition of the Sun is also that of the solar system.  

To determine the proportion of the elements in the Sun, we make use of the energy levels between the electron orbitals of the atoms of the different elements. The electromagnetic spectra of the Sun were noted to contain dark lines in 1802 by Wollaston and later studied by Fraunhofer (early 1800's), indicating adsorption at selective wavelengths or energies. Radiation emerging from the Sun's interior passes though the gas of its photosphere (outermost visible layer), in which the different elements selectively absorb radiation whose wavelength corresponds to the difference in the energy (E = hc/l) levels of its electron orbitals. The intensity of the absorption lines is a measure of the proportion of each element. 

Solar Spectrum

There is a saw-toothed exponential drop off in the abundances of the elements with increasing atomic number, with even numbered elements are always more abundant than adjacent odd numbered elements (Oddo-Harkins rule). The latter presumable reflects the fact that 4He nuclei are the basic component of most element formation reactions in stars. Notice the spike in abundances centered on Fe.

An analysis of the electromagnetic spectra of the Sun indicates that apart Hydrogen and Helium (98 wt.%), 8 other elements constitute 99 wt.% of the remaining matter (C, N, Ne, O, Mg, Si, Fe).

Major Elements

  Element Sun (Solar System)

Earth's Crust Crystal Site

O 39.7 46.6 A

Fe 27.9 5.0 Y

Si 5.5 27.7 T

Mg 11.3 2.1 Y

Ca 1.3 1.3 X > W

Al 1.1 8.1 T ~ Y

Na 0.7 2.8 W > X

K 0.1 2.1 W

Si/Fe 0.197 5.5 (28 × Sun)

K/Fe 0.0036 0.42 (100 × Sun)

atomic units atomic units

T/Y 0.6 7.3

W/T 0.06 0.18

Dominant Mineral

Y2TO4

olivineWT4O8

feldspar

Compared to the Earth's crust, the Sun exhibits a number of important compositional differences. It is depleted in Si, Al, Na, and K, and enriched in Fe and Mg. What has caused these chemical differences between the Sun (~ solar nebula or the solar system as a whole) and the crust of the Earth, and the terrestrial planets in general?

This is the story of igneous petrology.

Terrestrial Planets

basalt orgranite crust

Crust represents only ~0.7 wt.% of the Earth

Fe-Ni

basalt orgranite crust

Fe-Ni

opx

cpx

oliv

Allende

Chondritic Meteorites = Sun

Sun Mantle (~68 wt.%) + Fe-metal core (~31 wt.%)~SiO2 + MgO + FeO ~ 90+%

The Earth’s upper mantle is similar in composition to the Sun minus enough Fe to form the core. The Earth’s mantle is composed of a rock called peridotite, which consists largely of the minerals olivine and pyroxene

Silicon

Magnesium Iron

basalt orgranite crust

Fe-Ni

Mantle Xenoliths

Chondritic Meteorite

+ IronMetal

In core

Iron

basalt orgranite crust

peridotite mantle

olivine

feldspar

= Sun

Rain drop of

the Sun

SiO2 45.2 49.4 60.3

TiO2 0.7 1.4 1.0

Al2O3 3.5 15.4 15.6

MgO 37.5 7.6 3.9 FeO 8.5 10.1 7.2 CaO 3.1 12.5 5.8 Na2O 0.6 2.6 3.2

K2O 0.1 0.3 2.5

Total 99.2 99.3 99.5

Cations normalized to 100 cations Si 38.5 46.1 56.4 Ti 0.5 1.0 0.7 Al 3.6 16.9 17.2 Mg 47.6 10.6 5.4 Fe 6.0 7.9 5.6 Ca 2.8 12.5 5.8 Na 0.9 4.7 5.8 K 0.1 0.5 3.0 O 140.2 153.0 161.3

Mineralogy (oxygen units, XFe3+ = 0.10) Quartz 0.0 0.0 13.0 Feldspar 13.2 57.3 64.3 Clinopyroxene 6.7 25.7 5.9 Orthopyroxene 18.3 4.1 14.7 Olivine 59.9 9.9 0.0 Oxides 1.8 3.0 2.0

Mantle Ocean Continent crust crust

Oceanic crust - MORB basalt - p

Continental crust - granite - e

ContinentalCrust

Oceanic Crust

Solid – Liquid Fractionation

The diversity of igneous rocks is a reflection of the fact that in a partially melted multi-component system, the composition of the liquid will typically be different than the composition of the solid with which it coexists.

Any physical process that separates crystals from liquid, in such a system, will produce a chemical fractionation.

liq

oliv

Solid Source Refractory Solid + Liquid Restite

Refractory Mantle + Oceanic Crust

Cpx-rich PeridotiteLherzolite

Olivine-rich Peridotite + Basalt Harzburgite

Partial Melting of the Mantle

Fertile Mantle

Whole = Σ Parts

Lever Rule: p/R = x/y

y

x

R

amount of basalt (P) infertile mantle = x/(x+y)

Oceanic Crust

Oceanic Crust

Parent Magma Crystal Cumulate + Residual Magma

Volcanic RocksPlutonic or

Intrusive Rocks

Mafic Magma Gabbroic Cumulate + Felsic Magma

Volcanic rocks approximate the compositions of magmatic liquids. They represent aliquots of liquid that have escaped to the surface. The compositional variation observed in the liquids that the volcanic rocks represent is produced by varying degrees of crystal fractionation of a largely “gabbroic” mineral assemblage that now comprises plutonic intrusions.

Crystal Fractionation of Basalt

Whole = Σ Parts

Lever Rule: e/C = x/y

y

x

amount of granitein basalt = x/(x+ y)C

Continental Crustal GranitoidsSecond Stage Melting of Basalt

The majority of crustal granitoids are, however, thought to be liquids produced at the eutectic point e by the second stage melting of silica-saturated basaltic/gabbroic mafic crust, consisting largely of pyroxene and plagioclase.

e

ContinentalCrust

SiO2 45.2 49.4 60.3

TiO2 0.7 1.4 1.0

Al2O3 3.5 15.4 15.6

MgO 37.5 7.6 3.9 FeO 8.5 10.1 7.2 CaO 3.1 12.5 5.8 Na2O 0.6 2.6 3.2

K2O 0.1 0.3 2.5

Total 99.2 99.3 99.5

Cations normalized to 100 cations Si 38.5 46.1 56.4 Ti 0.5 1.0 0.7 Al 3.6 16.9 17.2 Mg 47.6 10.6 5.4 Fe 6.0 7.9 5.6 Ca 2.8 12.5 5.8 Na 0.9 4.7 5.8 K 0.1 0.5 3.0 O 140.2 153.0 161.3

Mineralogy (oxygen units, XFe3+ = 0.10) Quartz 0.0 0.0 13.0 Feldspar 13.2 57.3 64.3 Clinopyroxene 6.7 25.7 5.9 Orthopyroxene 18.3 4.1 14.7 Olivine 59.9 9.9 0.0 Oxides 1.8 3.0 2.0

Mantle Ocean Continent crust crust

Oceanic crust - MORB basalt p

Continental crust - granite e

Spectrum of Igneousliquids