GEOL 5310
ADVANCED IGNEOUS AND
METAMORPHIC PETROLOGY
Chemistry of Igneous Rocks
Nov. 2, 2009
WHOLE ROCK ANALYSIS OF A BASALT
Molecular
Wt%
Wt.
49.2
2.03
16.1
2.72
7.77
0.18
6.44
10.5
3.01
0.14
0.23
0.7
0.95
99.97
structural water
SiO2
TiO2
Al2O3
Fe2O3
FeO
MnO
MgO
CaO
Na2O
K2O
P2O5
H2O+
H2O-
adsorbed water Trace
Ba
Co
Cr
Ni
Pb
Rb
Wt%/
Mol. Wt. Mole%
60.09
95.9
101.96
159.7
71.85
70.94
40.31
56.08
61.98
94.2
70.98
18.02
18.02
0.8188
0.0212
0.1579
0.0170
0.1081
0.0025
0.1598
0.1872
0.0486
0.0015
0.0032
0.0388
0.0527
1.6174
Elements (ppm)
5
32
220
87
1.29
1.14
Sr
Th
U
V
Zr
La
190
0.15
0.16
280
160
5.1
50.62
1.31
9.76
1.05
6.69
0.16
9.88
11.58
3.00
0.09
0.20
2.40
3.26
100.00
Major elements:
usually > 1 wt.%
control properties of magmas
major constituents of essential
minerals
Minor elements:
usually 0.1 – 1 wt.%
substitutes for major elements in
essential minerals or may form small
amounts of accessory mins.
Trace elements:
usually < 0.1 wt.%
substitutes for major and minor elements
in essential and accessory minerals
1 wt.% = 10,000 ppm
1 ppm = 0.0001 wt.%
ANALYTICAL TECHNIQUES
Emitted
radiation
Energy Source
Emission
Detector
Absorbed
radiation
Sample
Output with
emission peak
Absorption
Detector
Whole Rock Analyses
- X-ray Fluorescence (XRF)
X-rays excite inner shell electrons producing
secondary X-rays
- Inductively Coupled Plasma (ICP)
dissolved rock mixed with Ar gas is turned into
plasma which excites atoms; generates X-rays
- Instrumental Neutron Activation (INAA)
nuclei bombarded with neutrons turning atoms
radioactive; measure emitted X-rays
- Mass Spectrometry(MS)
atoms ionized and propelled through a curved
electromagnet which seperates the ions by weight
(good for isotope analysis)
Output with
absorption trough
Mineral Chemical Analyses
- Electron Microprobe (EM)
incident electron beam generates X-rays
which whose characteristic wavelengths
are measured (WDS)
- Energy Dispersive Spectrometry (EDS)
incident electron beam generates X-rays
which whose characteristic energies are
measured; attached to UMD’s SEM
- X-ray Diffractometry(XRD)
Incident X-rays are diffracted by
characteristic mineral structure
CHEMICAL ANALYSES OF COMMON ROCK TYPES
THAT APPROXIMATE MAGMA COMPOSITIONS
Magma - Ultramafic
Rock SiO2
TiO2
Al2O3
Fe2O3
FeO
MnO
MgO
CaO
Na2O
K2O
H2O+
Total
Mafic
Intermed.
Peridotite
42.26
0.63
4.23
3.61
6.58
0.41
31.24
5.05
0.49
0.34
3.91
Basalt
49.20
1.84
15.74
3.79
7.13
0.20
6.73
9.47
2.91
1.10
0.95
Andesite
57.94
0.87
17.02
3.27
4.04
0.14
3.33
6.79
3.48
1.62
0.83
98.75
99.06
99.3
Felsic
Alkalic
Rhyolite Phonolite
72.82
56.19
0.28
0.62
13.27
19.04
1.48
2.79
1.11
2.03
0.06
0.17
0.39
1.07
1.14
2.72
3.55
7.79
4.30
5.24
1.10
1.57
99.50
99.23
CIPW NORMATIVE CALCULATIONS
Mode is the volume % of minerals observed
 Norm is the weight % of minerals calculated from
whole rock geochemical analyses by distributing
major elements among rock-forming minerals

Numbers show the order that
mineral are figured.
See Winter (2001) Appendix for
instructions.
13)
14)
15)
11)
7)
8)
9)
10)
12)
4)
5)
2)
1)
6)
3)
GEOCHEMICAL PLOTS
Objective: to show the co-variation of elemental
components that may give insight to magmatic
processes such aspartial melting
 magma mixing
 country rock assimilation/contamination
 fractional crystallization
(or crystallization differentiation)

Types:
bivariate (X-Y)
 triangular
 normalization plots (spider diagrams)

MOST PLOTS ARE APPROPRIATE FOR
LIQUID COMPOSITIONS ONLY!!!
HARKER
VARIATION
DIAGRAMS
Liquid
Lines of
Descent
Variation of major and
minor oxide abundances
vs. SiO2 (thought to be and
indication of the evolved character
of a magmatic system)
The “Daly” Gap
Real or an artifact of
the variation of SiO2
concentration with
differentiation
Winter (2001) Figure 8-2. Harker
variation diagram for 310
analyzed volcanic rocks from
Crater Lake (Mt. Mazama),
Oregon Cascades. Data compiled
by Rick Conrey (personal
communication).
Primitive
Evolved
DIFFERENTIATION INDEXES
from Winter (2001)
INTERPRETING TRENDS ON
VARIATION DIAGRAMS
Extraction Calculations
Addition-Subtraction Diagram
Figure 8.7.
Stacked variation
diagrams of
hypothetical
components X
and Y (either
weight or mol %).
P = parent, D =
daughter, S = solid
extract, A, B, C =
possible extracted
solid phases. For
explanation, see text.
From Ragland (1989).
Basic Analytical
Petrology, Oxford Univ.
Press. (From Winter
Rollinson (1993)
INTERPRETING TRENDS ON
VARIATION DIAGRAMS
Scattered Trends
-not all liquids
-not comagmatic
-polybaric fractionation
-sample heterogeneity
-varied data sources
MAGMA SERIES
RELATED TO TECTONIC PROVINCES
Subalkaline
Characteristic
Plate Margin
Series
Convergent Divergent
Alkaline
yes
Tholeiitic
yes
yes
Calc-alkaline
yes
Within Plate
Oceanic Continental
yes
yes
yes
yes
16
Phonolite
14
Tephriphonolite
12
Na2O + K2O
10
Na 2O+K 2O
Trachyte
PhonoTephrite
Foidite
Trachy- Trachydacite
andesite
Rhyolite
Basaltic
Tephrite
trachyBasaniteTrachy-andesite
basalt
Dacite
Andesite
Basaltic
Basalt
andesite
Picrobasalt
8
6
4
2
0
Winter (2001) Figure 8.11. Total alkalis vs. silica diagram for
the alkaline and sub-alkaline rocks of Hawaii. After MacDonald
(1968). GSA Memoir 116
35
40
45
50
55
SiO
SiO
22
60
65
70
75
SUBALKALINE DISCRIMINATION DIAGRAMS
AFM Diagram
Calc-Alkaline
Fe2O3 + FeO
20
Tholeiitic--Calc-Alkaline
boundary after Irvine and
Baragar (1971). Can. J. Earth
Sci., 8, 523-548
Al 2O3
15
10
100
Tholeiitic
90
80
70
AN
Na2O + K2O
MgO
60
50
40
ALUMINA/ALKALI DISCRIMINATION DIAGRAMS
Winter (2001) Figure 18.2. Alumina saturation classes
based on the molar proportions of
Al2O3/(CaO+Na2O+K2O) (“A/CNK”) after Shand (1927).
Common non-quartzo-feldspathic minerals for each
type are included. After Clarke (1992). Granitoid
Rocks. Chapman Hall.
Winter (2001) Figure 8-10 b. Alumina saturation
indices (Shand, 1927) with analyses of the
peraluminous granitic rocks from the Achala
Batholith, Argentina (Lira and Kirschbaum, 1990). In
S. M. Kay and C. W. Rapela (eds.), Plutonism from
Antarctica to Alaska. Geol. Soc. Amer. Special
Paper, 241. pp. 67-76.
TECTONIC
PROVINCE
DISCRIMINATION
DIAGRAMS
Rollinson (1993)
TECTONIC PROVINCE DISCRIMINATION DIAGRAMS
Figure 9.8 Examples of discrimination diagrams used to infer tectonic setting of ancient (meta)volcanics. (a) after Pearce and Cann
(1973), (b) after Pearce (1982), Coish et al. (1986). Reprinted by permission of the American Journal of Science, (c) after Mullen
(1983) Copyright © with permission from Elsevier Science, (d) and (e) after Vermeesch (2005) © AGU with permission.
TRACE ELEMENTS IN IGNEOUS PROCESSES
Ionic Field Strength
(Charge/Radius)
Transition Metals
Precious
Metals
Rare Earth Elements
Goldschmidt’s (1937) Rules of Element Affinity
1.
2.
Two ions with the same valence and radius should
exchange easily and enter a solid solution in amounts equal
to their overall proportions (e.g. Rb~K, Ni~Mg, Mn~Fe)
If two ions have a similar radius and the same valence: the
smaller ion is preferentially incorporated into the solid over
the liquid (e.g., Mg > Fe in Olivine)
TRACE ELEMENT COMPATIBILITY
Compatibility – degree to which an element prefers to partition into the solid over
the liquid phase .
Kd(i)1 – Mineral-Liquid Partition Coefficient for element i in mineral 1
Kd(i)1 = C(i)mineral 1/ C(i)liquid
(C(i) - concentration of element i in wt. %)
Kd(i)1 > 1 – Compatible,
Kd(i)1 < 1 – Incompatible
D(i) – Bulk Rock Partition Coefficient for element i
D(i) = x1 Kd(i)1 + x2 Kd(i)2 + x3 Kd(i)3 + ....
(x1 – proportion of mineral 1)
INCOMPATABILITY OF TRACE ELEMENTS
PARTITION COEFFICIENTS (CS/CL)
Rb
Sr
Ba
Ni
Cr
La
Ce
Nd
Sm
Eu
Dy
Er
Yb
Lu
Rare Earth Elements
Table 9-1. Partition Coefficients (CS/CL) for Some Commonly Used Trace
Elements in Basaltic and Andesitic Rocks
Olivine
0.010
0.014
0.010
14
0.70
0.007
0.006
0.006
0.007
0.007
0.013
0.026
0.049
0.045
Opx
0.022
0.040
0.013
5
10
0.03
0.02
0.03
0.05
0.05
0.15
0.23
0.34
0.42
Data from Rollinson (1993).
Cpx
Garnet
0.031
0.042
0.060
0.012
0.026
0.023
7
0.955
34
1.345
0.056
0.001
0.092
0.007
0.230
0.026
0.445
0.102
0.474
0.243
0.582
1.940
0.583
4.700
0.542
6.167
0.506
6.950
Plag
Amph Magnetite
0.071
0.29
Compatible
1.830
0.46
0.23
0.42
0.01
6.8
29
0.01
2.00
7.4
0.148
0.544
2
0.082
0.843
2
0.055
1.340
2
0.039
1.804
1
0.1/1.5*
1.557
1
0.023
2.024
1
0.020
1.740
1.5
0.023
1.642
1.4
0.019
1.563
* Eu3+/Eu2+
Italics are estimated
BEHAVIOR OF TRACE ELEMENTS DURING
PARTIAL (BATCH) MELTING
Normal Range
of Partial
Melting in the
Mantle
CL/Co = 1/[D(i)(1-F) + F]
F - Fraction of Liquid
D(i)- Bulk Distribution
Coefficient for Element i
As D(i)  0 (strongly IE)
CL/Co ≈ 1/F
Degree of
Partial
Melting (F)
Incompatible
Compatible
BEHAVIOR OF RARE EARTH ELEMENTS DURING
PARTIAL (BATCH) MELTING OF THE MANTLE
From Rollinson (1993)
Winter (2001) Figure 9-4. Rare Earth concentrations
(normalized to chondrite) for melts produced at various
values of F via melting of a hypothetical garnet lherzolite
using the batch melting model (equation 9-5).
BEHAVIOR OF TRACE ELEMENTS DURING
FRACTIONAL CRYSTALLIZATION
Rayleigh Distillation:
CL/Co = F(D(i)-1)
F - Fraction of Liquid Remaining
D(i)- Bulk Distribution
Coefficient for Element i
From Rollinson (1993)
BEHAVIOR OF TRACE ELEMENTS DURING FRACTIONAL
CRYSTALLIZATION
Compatible
Bulk Rock Partition Coefficient of Ce,Yb, and Ni
for Crystallization of:
1) Troctolite (70% Pl, 30% Ol)
D(Ce) = xPl Kd(Ce)Pl + xOl Kd(Ce)Ol
= .7*.103 + .3*.007 = 0.092
D(Yb) = xPl Kd(Yb)Pl + xOl Kd(Yb)Ol
= .7*.07 + .3*.065 = 0.069
Incompatible
D(Ni) = xPl Kd(Ni)Pl + xOl Kd(Ni)Ol
= .7*.01 + .3*25= 7.5
2) Olivine Gabbro (63% Pl, 12% Ol, 25% Cpx)
D(Ce) = xPl Kd(Ce)Pl + xOl Kd(Ce)Ol + xCpx Kd(Ce)Cpx
= .63*.103 + .12*.007 + .25*.09 = 0.088
D(Yb) = xPl Kd(Yb)Pl + xOl Kd(Yb)Ol + xCpx Kd(Yb)Cpx
= .63*.07 + .12*.065 + .25*.09 = 0.074
D(Ni) = xPl Kd(Ni)Pl + xOl Kd(Ni)Ol + xCpx Kd(Ni)Cpx
= .63*.01 + .12*25 + .25*8 = 5
From Rollinson (1993)
TRACE ELEMENT BEHAVIOR DURING
FRACTIONAL CRYSTALLIZATION
Rayleigh Distillation: CL/Co = F(D-1)
100.000
100.000
CL/Co
Troctolite
CL/Co
Olivine Gabbro
10.000
10.000
Tr(Yb)
OG(Yb)
OG(Ce)
Ce/Yb
OG(Ni)
Tr(Ce)
Ce/Yb
Tr(Ni)
1.000
1.000
0.100
0.00
0.100
0.00
0.20
0.40
0.60
0.80
F (fraction of liquid remaining)
1.00
0.20
0.40
0.60
0.80
F (fraction of liquid remaining)
Conclusions: Fractional crystallization of mafic magmas gradually increases the
concentrations of similarly incompatible elements, but has a minimal effect on their
ratios; and strongly decreases the concentrations of compatible elements
1.00
TRACE ELEMENT BEHAVIOR DURING
FRACTIONAL CRYSTALLIZATION
EXAMPLE FROM THE SONJU LAKE INTRUSION
E. Compatible Elements
RARE EARTH ELEMENT(REE)DIAGRAMS
COMPARES RATIOS AND NORMALIZES TO A STANDARD COMPOSITION
Fractional crystallization of olivine from a komatiitic melt
REE commonly normalized
to chondrite composition –
thought to approximate the
unfractionated composition
of the earth.
Fractional crystallization
increases the REE abundance,
but has a neglible effect on the
REE pattern
Light REE
Heavy REE
From Rollinson (1993)
REE RATIO DIAGRAMS
From Rollinson (1993)
Fractional Crystallization
- minimal change in
REE ratios
Partial Melting
- significant
change in REE
ratios
TRACE ELEMENT NORMALIZATION PLOTS
(SPIDER DIAGRAMS)
Rock/Standard Comp*
Positive
Anomaly
Enriched
Negative
Anomaly
Depleted
Most
Least
Incompatible Elements
(likes magma)
Common Standard Compositions for Normalizing
• Chondritic meteorite
• Avg. Mid-ocean Ridge Basalt (MORB)
• Primitive Mantle
• Primitive Ocean Island Basalt (OIB)
Compatible
Elements
(likes minerals)