Transcript Introduction to Petrology

Introduction
to
Petrology
Francis 2014
Introductory Petrology EPSC-212B
Don Francis:
Documents:
Room: F.D.A. 316, [email protected]
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
- Variation diagrams, calc-alkaline versus tholeiitic suites
- Mafic Intrusions and cumulate rocks
- Volcanic rocks
Jan 16/17
Jan 20
Jan 22
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
- Mid-Term Test (10 marks)
- Sedimentary test (10 marks)
Feb 20/21
Feb 26
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
Philpotts, A.R., and Ague, J.J.; 2009: Principles of Igneous and
Metamorphic Petrology, Cambridge University Press.
Boggs, S.; 2012: Principles of Sedimentology and Stratigraphy.
Prentice Hall, New Jersey. QE471 B66.
T.A.s:
Ryan Libby
Gregor Lucic
Thomas Maguire
Volker Moeller
- FDA 346
- FDA 130A
- FDA 349
- FDA 346
Francis, Intro. Petrology EPSC 212, 2014
Required Component of Course Outlines
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, 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
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
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.
60%
basalt cube - % melted
70%
75%
Two Kinds of Igneous Rocks:
White/Light
Granitoids: light or felsic rocks
dominated by feldspar and quartz .
Constitute the continental crust.
Granite
Black/Dark
Basalt/gabbro: dark or mafic rocks
dominated by Fe-Mg silicates, such as
olivine, and pyroxenes.
Constitute the oceanic crust.
Basalt
Mantle - Ocean & Continent crust
Continental
Crust
Oceanic Crust
Oceanic crust
-
MORB basalt
Continental crust -
granite
-
-
e
p
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.
Major Elements
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).
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.
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
olivine
WT4O8
feldspar
Terrestrial Planets
basalt or
granite crust
Fe-Ni
Crust represents only ~0.7
wt.% of the Earth
basalt or
granite 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
basalt or
granite crust
Fe-Ni
Magnesium
Iron
Rain drop
of
the Sun
basalt or
granite crust
feldspar
peridotite
mantle
Iron
olivine
Chondritic
Meteorite
+ Iron
Metal
In core
Mantle
Xenoliths
= Sun
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
Continental
Crust
Oceanic Crust
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
-
-
e
p
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
Partial Melting of the Mantle
Solid Source
Refractory Solid
Restite
+
Liquid
Fertile Mantle
Refractory Mantle
+
Oceanic
Crust
Cpx-rich Peridotite
Lherzolite
Olivine-rich Peridotite
Harzburgite
+
Basalt
Oceanic
Crust
Whole = Σ Parts
Lever Rule: p/R = x/y
Oceanic Crust
amount of basalt (P) in
fertile mantle = x/(x+y)
y
x
R
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.
amount of granite
in basalt = x/(x+ y)
Cx
y
Continental Crustal Granitoids
Second Stage Melting of Basalt
Continental
Crust
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.
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