1. Trace Elements Ni Zr ppm wt. % SiO 40 50 60 70 80 100 200 300
100
200
300 Ni
SiO 2 Zr
ppm
wt. %
TE often vary by > 103 very useful since so sensitive to distr. & fractionation

2. Today’s lecture Updates: Topics: Finish major elements
Trace element compositions
Trace element behavior
Partitioning
Spider diagrams
TE often vary by > 103 very useful since so sensitive to distr. & fractionation

3. Magma Evolution Harker diagram Smooth trends Model with 3 assumptions:55 65 75 45 2 3 4 8 6 10 14 16
Al2O3
MgO
CaO
Fe2O3
Na2O
K2O
Wt. % SiO2 B BA A D RD R
Harker diagram
Smooth trends
Model with 3 assumptions:
1 Rocks are related
2 Trends = liquid line of descent (mineral control)
3 The basalt is the parent magma from which the others are derived
B=basalt, BA=basaltic-andesite, A=andesite, D=dacite, RD=rhyo-dacite, R=rhyolite

4. Magma Series

5. Alkali vs. Silica -- Hawaiian volcanics:12 10 8 6 4 2 35 40 45 50 55 60 65
%SiO2
%Na2O + K2O
Alkaline
Subalkaline
Figure Total alkalis vs. silica diagram for the alkaline (open circles) and sub-alkaline rocks of Hawaii. After MacDonald (1968). GSA Memoir 116

6. Evolving rocktypes, subalkaline subdivision
(F)
Rhyolite
Dacite
Andesite
Basaltic Andesite
Ferro-Basalt
Basalt
Calc-alkaline
Tholeiitic
B-A A D R
FeO + Fe2O3
K2O + Na2O
(A)
MgO
(M)

7. Occurrence of different series
Calc-alkaline only in subduction zones
Tholeiitic series anywhere
Alkaline not at Mid Ocean Ridges
After Wilson (1989). Igneous Petrogenesis. Unwin Hyman - Kluwer

8. The Basalt TetrahedronDi Q En
Critical plane of
silica
undersaturation Ne Ab
Plane of
silica saturation Fo Ol Ne Ab
Opx Q
Alkaline field
Subalkaline field
Dividing line
Figure Left: the basalt tetrahedron (after Yoder and Tilley, 1962). J. Pet., 3, 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,

9. Types of incompatible elements
W. White

10. Element Distribution Element fits in a crystal if similar:
Ionic size (xl lattice)
Charge (neutral crystal)
Goldschmidt’s rules
Ions of similar size (<15%) can replace each other
Ions of similar size and a charge difference of 1 can replace as long as neutrality is preserved
The ion with the higher ionic potential forms a stronger bond with the anions surrounding the crystal site
W. White
therefore some TE's will follow similar major E
Periodic Table is next slide

11. 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 = (mol) => D = (concentration by weight)
K = equilibrium constant (mol) ≈ D Cs Cl
Xi solid
Xi liquid

12. Compatibility Cs Cl
D =

13. Compatibility and minerals
Not exact, since D varies with the composition of mins & melt

14. 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

15. Enrichment/depletion40 50 60 70 80
100
200
300 Ni
SiO 2 Zr
ppm
wt. %
TE often vary by > 103 very useful since so sensitive to distr. & fractionation

16. 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
K/Rb for amphibole:
Usually behave similarly, so ~ constant ratio
Unless amphibole which has a D of about 1.0 for K and 0.3 for Rb
almost all K and Rb reside in it
Melt of amphibole-bearing rock will -> decrease K/Rb in the partial melt
Other factors being equal, a magma produced by partial melting of an amphibole-bearing source rock would have a lower K/Rb than one derived from amphibole-free source
High absolute K or Rb could also  an amphibole-bearing source, but may result from other causes (high phlogopite, or an alkali-enriched fluid)
The ratio is more indicative of amphibole due to the different D values
Fractional crystallization of amphibole would also -> low K/Rb ratio in the evolved liquid

17. La Ce Nd Sm Eu Tb Er Dy Yb Lu
REE Diagrams
Concentration
La Ce Nd Sm Eu Tb Er Dy Yb Lu

18. Odd-Even in the Solar System
What’s interesting/strange about this pattern?
Chondrite normalization:
Normalize to chondrite meteorites to:
1) avoid Oddo-Harkins (even Z more common)
2) think chondrite = primitive earth, so can compare to initial distribution

19. Normalized diagrams ? sample/chondrite L 0.00 2.00 4.00 6.00 8.00
10.00 56 58 60 62 64 66 68 70 72
sample/chondrite L
La Ce Nd Sm Eu Tb Er Yb Lu ?

20. Spider Diagrams 1 10
100
1000 Rb Ba Th Nb K La Ce Sr Nd Sm Zr Ti Gd Y
Rock/Chondrites
Order of elements based on estimates of increasing incompatibility from right to left in a "typical" mantle undergoing partial melting
Elements are all incompatible (D<1) during most partial melting and fractional crystallization processes. The main exceptions are
Sr, which may be compatible if plagioclase is involved,
Y and Yb with garnet
Ti with magnetite
Troughs at these elements would indicate respective mineral involvement
Oceanic basalts = large degrees of PM, their spider diagrams should reflect the trace element patterns of their source
Less incompatible elements on the right-hand side should be less enriched during PM (particularly for small degrees of it), tilting the curve up on the left -> (-) slope
Additionally, FX subsequent to magma segregation from the source should tip the pattern even further
Fig 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

21. REE/Spider Diagrams II
0.00
2.00
4.00
6.00
8.00 56 58 60 62 64 66 68 70 72
Element
sample/chondrite
Eu*
La Ce Nd Sm Eu Tb Er Yb Lu 2 1
Eu* is the value Eu “should” have if Eu+2 did not -> plagioclase
Another example of how RATIOS can help
Eu alone is inconclusive (low REE of low Eu)
Sm/Eu is slope or Eu anomaly trough (Use Eu*/Eu anyway)
Figure 9-5. From Winter (2001) An Introduction to Igneous and Metamorphic Petrology. Prentice Hall.

22. Examples 67% Ol 17% Opx 17% Cpx La Ce Nd Sm Eu Tb Er Yb Lu
0.00
2.00
4.00
6.00
8.00
10.00 56 58 60 62 64 66 68 70 72
sample/chondrite
La Ce Nd Sm Eu Tb Er Yb Lu
67% Ol 17% Opx 17% Cpx
0.00
2.00
4.00
6.00
8.00
10.00
sample/chondrite
60% Ol 15% Opx 15% Cpx 10%Plag
La Ce Nd Sm Eu Tb Er Yb Lu
0.00
2.00
4.00
6.00
8.00
10.00 56 58 60 62 64 66 68 70 72
sample/chondrite
La Ce Nd Sm Eu Tb Er Yb Lu
57% Ol 14% Opx 14% Cpx 14% Grt

23. C 1 What’s Di? Di (1 F) F = - + Batch Melting D = 1 = even split,O = - +
0.1 1 10
100
1000
0.2
0.4
0.6
0.8 F
D = 0.001
D = 0.1
D = 0.5
D = 1
D = 2
D = 4
D = 10
CL/CO
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
D = No fractionation so CL/CO = 1 for all values of F
Figure 9-2. From Winter (2001) An Introduction to Igneous and Metamorphic Petrology. Prentice Hall.

24. Fractional melting, and others
Separation of each melt drop as it formed
CL/CO = (1/D) * (1-F) (1/D -1)
Crystallization like melting
Wall-rock assimilation
Zone refining
Combinations of processes
Can also apply the Rayleigh equation to Rayleigh fractional melting
Cox, Bell, Pankhurst