Igneous
Petrology
Francis 2013
Igneous Petrology: EPSC 423A, 2013
donald.francis@mcgill.ca
Lectures:
Tues & Thurs: 11:30 - 12:30 pm
Room: FDA 315
Lab: Thursday 2:30-5:30pm
Documents:
www.eps.mcgill.ca/~courses/c423/
Topics:
The Nature of Silicate Melts
Review of Thermodynamics and Simple Phase Diagrams
Phase Equilibria in Complex Systems at elevated P-T
Role of Volatiles
Behaviour of Trace Elements
Implications of Isotopes
Crust / Mantle Reservoirs
Fractionation Processes
Mid-Ocean Ridge Basalts
Ocean Island Basalt Suites
Flood Basalt Volcanism
Calc-Alkaline Magmatism
Ultra-Potassic and Carbonatitic Magmatism
Troctolite - Anorthosite Magmatic Suites
Komatiites and Archean Greenstone - Tonalite Terranes
Magmatism on the Moon, Venus, and Mars
Grading:
Final Theory Exam
Lab Reports
50%
50%
TA’s:
Grant Cox
Ryan Libbey
Jason Coumans
- FDA 311 (grant.cox@mail.mcgill.ca)
- FDA 312 (ryan.libbey@mail.mcgill.ca)
- FDA 202a (jason.coumans@mail.mcgill.ca)
Labs – reports worth 50%
A typed report will be required for each lab, typically due the following Thursday
before the next Lab.
You Will Work in Teams of ~2
1.
2.
3.
4.
5.
6.
7.
8.
9.
10.
11.
12.
Review of Common Rock Forming Minerals
Meteorites and the Mantle
Volcanic Textures, Cooling Rates, and Primary Magmas
Classification of Basalts: Baffin Island and Fort Selkirk
Plutonic Equivalents: The Monteregian Hills (with associated field trip)
Small Intrusions – the Dash Dyke
Large Layered Intrusions – Muskox, Bushveld, Raudot.
Graphical & Numerical Analysis of Crystal Fractionation
Eocene Calc-Alkaline Volcanism
Eocene Granitoid Plutonism
Kimberlites, carbonatites, and other exotica
Precambrian greenstones and granitoids
NB:
Get Microscope and download AlphaMelts program during the first lab, Thursday, Sept. 5.
All questions such as: my microscope does not work, where are the thin sections, who has the rock
samples, etc. should be directed to the TA’s.
Francis, Igneous Petrology EPSC 423A, 2013
Field Trip
Saturday, Oct. 5
Mount St.
Hilaire
The Monteregian Hills
Rougemont
Mount
Yamaska
References on Reserve in PSE Library and/or
my Office
Theory:
Winter, J.D.; 2001: An Introduction to Igneous and Metamorphic Petrology. Prentice
Hall, QE461.W735 2001.
Philpotts,A.R., & Ague, J.J.; 2009: Priciples of Igneous and Metamorphic Petrology.
Cambridge University Press, QE461.P572
Ehlers, E.G.; 1972: The Interpretation of Geological Phase Diagrams. Freeman, San
Francisco, QE364 E35
Rocks in Thin Section:
Nesse, W.D., 2004: Introduction to Optical Mineralogy, 348p. Oxford University, Press,
QE369.06 N47
Williams, H., Turner, F.J., & Gilbert, C.M.; 1982: Petrography: An introduction to the study
of rocks in thin section. Freeman, San Francisco, QE434 W73.
Francis, Igneous Petrology EPSC 423A, 2013
Required Component of Course Outlines
Jane Everett, Dean of Students.
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.
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).
Francis, Igneous Petrology EPSC 423A, 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
Francis, Igneous Petrology EPSC 423A, 2013
Diversity of igneous rocks reflects the action of
crystal – liquid fractionation
processes at high temperature
Solid(xyl)
K
Liquid(liq)
glass
Elemental partitioning between coexisting solid and liquid
Cxyli / Cliqi
=
Ki
followed by the physical separation of solid(s) and liquid
0livine
constant
temperature
(Fe/Mg)oliv / (Fe/Mg)liq ~ 0.3
Francis, Igneous Petrology EPSC 423A, 2013
Two Kinds of Igneous Rocks:
White/Light
Granitoids: light or felsic rocks
dominated by feldspar and quartz that
Granite
Constitute the continental crust.
Black/Dark
Basalt/gabbro: dark or mafic rocks
dominated by Fe-Mg silicates, such as
olivine, and pyroxenes.
Basalt
Constitute the oceanic crust.
Igneous Rocks reflect magmatic
processes in an evolving Earth
Francis, Igneous Petrology EPSC 423A, 2013
Composition of the Sun and the Cosmic
Abundances of the Elements:
The Sun constitutes 99.98 wt.% of the solar
system, thus 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 was 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.
Francis, Igneous Petrology EPSC 423A, 2013
Solar Spectrum
The Sun constitutes 99.98 wt.% of the solar
system, thus the chemical composition of
the Sun is also that of the solar system.
O, Si, Mg, Fe constitute more than 91%
of Condensed Sun’s Composition
>92%
Major Elements
Chondritic Meteorites
have the same solid
composition as the Sun ~
Solar System
Francis, Igneous Petrology EPSC 423A, 2013
Mantle Xenoliths:
Olivine – rich Peridotite nodules of the Earth’s mantle brought to the surface by
volcanoes.
Francis, Igneous Petrology EPSC 423A, 2013
Sun - Chondritic Meteorites - Earth’s Mantle
Sun
~
BulkSilicateEarth (~68 wt.%) + Fe-metal core (~31 wt.%)
The Earth’s upper mantle is similar
in composition to BSE, and is
composed of a rock called
peridotite, which consists largely of
the
minerals
olivine
and
orthopyroxene
basalt or
granite crust
peridotite
mantle
Fe-Ni
metallic
core
Francis, Igneous Petrology EPSC 423A, 2013
SiO2 + MgO + FeO
~ 91%
basalt or
granite crust
feldspar
peridotite
mantle
Iron
olivine
Chondritic
Meteorite
= Sun
+ Iron
Metal
Mantle
Xenoliths
Francis, Igneous Petrology EPSC 423A, 2013
Terrestrial Planets
basalt or
granite crust
peridotite
mantle
Crust represents only ~0.7
wt.% of the Earth
Fe-Ni
metallic
core
Francis, Igneous Petrology EPSC 423A, 2013
Mantle Ocean Continent
crust crust
SiO2
TiO2
Al2O3
MgO
FeO
CaO
Na2O
K2O
Total
45.2
0.7
3.5
37.5
8.5
3.1
0.6
0.1
99.2
49.4
1.4
15.4
7.6
10.1
12.5
2.6
0.3
99.3
60.3
1.0
15.6
3.9
7.2
5.8
3.2
2.5
99.5
Cations normalized to 100 cations
Si
Ti
Al
Mg
Fe
Ca
Na
K
O
38.5
0.5
3.6
47.6
6.0
2.8
0.9
0.1
140.2
46.1
1.0
16.9
10.6
7.9
12.5
4.7
0.5
153.0
56.4
0.7
17.2
5.4
5.6
5.8
5.8
3.0
161.3
Mineralogy (oxygen units, XFe3+ = 0.10)
Quartz
Feldspar
Clinopyroxene
Orthopyroxene
Olivine
Oxides
0.0
13.2
6.7
18.3
59.9
1.8
0.0
57.3
25.7
4.1
9.9
3.0
13.0
64.3
5.9
14.7
0.0
2.0
Oceanic crust
-
MORB basalt
Continental crust -
granite
p
e
Francis, Igneous Petrology EPSC 423A, 2013
Partial Melting of the Mantle
Solid Source
Fertile Mantle
Cpx-rich Peridotite
Lherzolite
Refractory Solid
Restite
+
Refractory Mantle
+
Olivine-rich Peridotite
Harzburgite
Liquid
Oceanic
Crust
+
Basalt
Whole = Σ Parts
Lever Rule: p/R = x/y
amount of basalt (P) in
fertile mantle = x/(x+y)
y
~ 15-20%
x
R
Francis, Igneous Petrology EPSC 423A, 2013
Crystal Fractionation of Basalt
Parent Magma
Crystal Cumulate + Residual Magma
Plutonic
or
Intrusive Rocks
Mafic Magma
Volcanic Rocks
Gabbroic Cumulate + Felsic Magma
Whole = Σ Parts
Lever Rule: e/C = x/y
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.
Francis, Igneous Petrology EPSC 423A, 2013
amount of granite
in basalt = x/(x+y)
Cx
~ 10%
y
Continental Crustal Granitoids
Second 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 silicasaturated basaltic/gabbroic mafic
crust, consisting largely of pyroxene
and plagioclase.
Francis, Igneous Petrology EPSC 423A, 2013
e
Mantle Ocean Continent
crust crust
SiO2
TiO2
Al2O3
MgO
FeO
CaO
Na2O
K2O
Total
45.2
0.7
3.5
37.5
8.5
3.1
0.6
0.1
99.2
49.4
1.4
15.4
7.6
10.1
12.5
2.6
0.3
99.3
60.3
1.0
15.6
3.9
7.2
5.8
3.2
2.5
99.5
Spectrum of Igneous
liquids
Cations normalized to 100 cations
Si
Ti
Al
Mg
Fe
Ca
Na
K
O
38.5
0.5
3.6
47.6
6.0
2.8
0.9
0.1
140.2
46.1
1.0
16.9
10.6
7.9
12.5
4.7
0.5
153.0
56.4
0.7
17.2
5.4
5.6
5.8
5.8
3.0
161.3
Mineralogy (oxygen units, XFe3+ = 0.10)
Quartz
Feldspar
Clinopyroxene
Orthopyroxene
Olivine
Oxides
0.0
13.2
6.7
18.3
59.9
1.8
0.0
57.3
25.7
4.1
9.9
3.0
13.0
64.3
5.9
14.7
0.0
2.0
Oceanic crust
-
MORB basalt
Continental crust -
granite
p
e
Francis, Igneous Petrology EPSC 423A, 2013