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Trace Elements
300
Ni
200
100
ppm
0
300
Zr
200
100
0 40
50
60
SiO 2
70
wt. %
80
Today’s lecture
Updates:
Topics:
•Finish major elements
•Trace element compositions
•Trace element behavior
•Partitioning
•Spider diagrams
Magma Evolution
Harker diagram
B
BA
A
D RD
R
16
Al2O3
14
Smooth trends
 Model with 3 assumptions:
MgO
1 Rocks are related
2 Trends = liquid line of
descent (mineral control)
3 The basalt is the parent
Na O
magma from which the
others are derived
10

2
6
8
2
4
0
8
4
4
CaO
0
3
2
4
2
B=basalt, BA=basaltic-andesite, A=andesite,
D=dacite, RD=rhyo-dacite, R=rhyolite
Fe2O3
0
45
55
65
Wt. % SiO
75
K2O
Magma Series
Alkali vs. Silica -- Hawaiian volcanics:
12
10
Alkaline
8
6
4
2
Subalkaline
35
40
45
50
%SiO
55
60
65
Evolving rocktypes,
subalkaline subdivision
FeO + Fe2O3
Tholeiitic
B-A
A
D
R
Calc-alkaline
K2O + Na2O
MgO
Occurrence of different series
Calc-alkaline only in subduction zones
Tholeiitic series anywhere
Alkaline not at Mid Ocean Ridges
Characteristic
Plate Margin
Series
Convergent Divergent
Alkaline
yes
Tholeiitic
yes
yes
Calc-alkaline
yes
Within Plate
Oceanic Continental
yes
yes
yes
yes
After Wilson (1989). Igneous Petrogenesis. Unwin Hyman - Kluwer
The Basalt Tetrahedron
Di
Ol
Critical plane
of silica
undersaturation
Plane of
silica saturation
Ab
Ne
Opx
Q
En
Fo
Figure 8-12. Left: the basalt tetrahedron (after Yoder and
Tilley, 1962). J. Pet., 3, 342-532. Right: the base of the
basalt tetrahedron using cation normative minerals, with
the compositions of subalkaline rocks (black) and
alkaline rocks (gray) from Figure 8-11, projected from
Cpx. After Irvine and Baragar (1971). Can. J. Earth Sci.,
8, 523-548.
Ne
Ab Dividing line
Q
Types of incompatible elements
W. White
Element
Distribution
Element fits in a crystal if
similar:

Ionic size (xl lattice)

Charge (neutral crystal)
Goldschmidt’s rules
1. Ions of similar size (<15%) can replace each other
W. White
2. Ions of similar size and a charge difference of 1 can replace as
long as neutrality is preserved
3. The ion with the higher ionic potential forms a stronger bond
with the anions surrounding the crystal site
Chemical Fractionation

The uneven distribution of an ion between
two competing phases (melt-xl)
Exchange equilibrium of a component i between
two phases (solid and liquid)
i (liquid) <=> i (solid)
K=
Xi solid
Xi liquid
(mol)
=> D =
Cs
Cl
(concentration by weight)
K = equilibrium constant (mol) ≈ D
Compatibility
Cs
D= C
l
Compatibility and minerals
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
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
Bulk distribution

For a rock, determine the bulk distribution
coefficient D for an element by adding up the
minerals
DEr = (0.6 · 0.026) + (0.25 · 0.23) + (0.10 · 0.583) + (0.05 · 4.7) = 0.366
60% olivine, D = 0.026
25% orthopyroxene, D = 0.23
10% clinopyroxene, D = 0.583
5% garnet, D = 4.7
Enrichment/depletion
300
Ni
200
100
ppm
0
300
Zr
200
100
0 40
50
60
SiO 2
70
wt. %
80
Trace element behavior
Examples of using trace element ratios to evaluate crystallizing minerals:
Incompatible examples:
K/Rb often used for amphibole:
least incompatible in amph => controls K/Rb with its D values
Sr and Ba actually compatible in plagioclase and alkali feldspar, resp.
=> start of fsp crystallization significantly changes bulk D and ends
enrichment
Compatible example:
Ni strongly fractionated  olivine
Cr and Sc  pyroxenes
=> Ni/Cr or Ni/Sc can distinguish the effects of olivine and augite in a
partial melt or a suite of rocks produced by fractional crystallization

Concentration
REE Diagrams
La Ce Nd Sm Eu Tb Er Dy Yb Lu
Odd-Even in the Solar System
What’s interesting/strange about this pattern?
Log (Abundance in CI Chondritic Meteorite)
11
H
He
10
9
8
C
7
6
5
4
3
2
1
Li
O
Ne MgSi
Fe
N
S Ar
Ca Ni
Na
Ti
AlP
K
F Cl
V
B
Sc
Sn
Ba
Pt Pb
0
Be
-1
Th
-2
U
-3
0
10
20
30
40
50
60
Atomic Number (Z)
70
80
90
100
Normalized diagrams
sample/chondrite
10.00
8.00
6.00
?
4.00
2.00
0.00
56 La58
Ce
L
60Nd 62Sm 64
Eu
66
Tb
68Er 70 Yb 72
Lu
Spider Diagrams
Rock/Chondrites
1000
100
10
1
Rb Ba Th
Nb
K La Ce Sr Nd Sm Zr Ti Gd Y
Fig. 9-5. Spider diagram for an alkaline basalt from Gough Island,
southern Atlantic. After Sun and MacDonough (1989). In A. D.
Saunders and M. J. Norry (eds.), Magmatism in the Ocean Basins.
Geol. Soc. London Spec. Publ., 42. pp. 313-345.
REE/Spider Diagrams II
sample/chondrite
8.00
Eu*
2
6.00
1
4.00
2.00
0.00 56La Ce
58
Nd
60
Sm Eu
62
64
Tb
66
Er Yb Lu
68
70
72
Element
Figure 9-5. From Winter (2001) An Introduction to Igneous and Metamorphic Petrology. Prentice Hall.
Examples
10.00
67% Ol
sample/chondrite
8.00
17% Opx
17% Cpx
6.00
4.00
2.00
0.00
56
58 Ce 60 Nd 62Sm Eu
64 Tb66
La
68
Er
70 Lu 72
Yb
10.00
10.00
57% Ol
8.00
14% Opx
14% Cpx 14% Grt
8.00
sample/chondrite
sample/chondrite
60% Ol 15% Opx 15% Cpx 10%Plag
6.00
4.00
6.00
4.00
2.00
2.00
0.00
0.00
La Ce Nd Sm Eu
Tb
Er
Yb Lu
56
58
La
64
Ce60 Nd 62Sm Eu
Tb66
68
Er
70 Lu
Yb
72
Batch Melting
CL =
1
What’s Di?
C O Di(1 - F)+ F
CL, CO = liquid, solid concentration
F = fraction melt produced
= melt/(melt + rock)
D = 1 = even split,
 D < 1 = incompatible in
minerals => enriched in melt
 D > 1 = compatible in
minerals => depleted in melt

1000
100
D = 0.001
10
CL/CO
D = 0.1
D = 0.5
D=1
D=2
1
D=4
D = 10
0.1
0
0.2
0.4
0.6
0.8
F
Figure 9-2. From Winter (2001) An Introduction to Igneous and Metamorphic Petrology. Prentice Hall.
1
Fractional melting, and others
Separation of each melt drop as it formed
CL/CO = (1/D) * (1-F) (1/D

Crystallization like melting

Wall-rock assimilation

Zone refining
Combinations of processes

Cox, Bell, Pankhurst
-1)