1. Trace Elements Note magnitude of major element changes wt %
Element Distribution...as a tool in the interpretation of the history of igneous rocks
Different elements have diff. affinities for environments to reside: Si later melts - Mg early xls.
Remember from Chapter 1: A. Goldschmidt:
some elements metals "Siderophile" Fe, Pt, Mo
some elements sulfides "Chalcophile" S,Cu,Zn
some elements silicates "Lithophile" Si,K,Ca,REE
SIMPLISTIC Xl Field Theory best results. Study of elec. envir. in lattice & melt...
Trace Elements: very low conc.
TE's don't govern the appearance of a phase (as K req. Ksp or Bi), but enter various phases by substitution.
Compare Harkers
Major E usually vary by < 101
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). From Winter (2001) An Introduction to Igneous and Metamorphic Petrology. Prentice Hall.

2. Trace Elements Note magnitude of trace element changes ppm ppm
TE often vary by > 103 very useful since so sensitive to distr. & fractionation
ppm
Figure 9-1. Harker Diagram for Crater Lake. From data compiled by Rick Conrey. From Winter (2001) An Introduction to Igneous and Metamorphic Petrology. Prentice Hall.

3. Element Distribution Goldschmidt’s rules (simplistic, but useful)
1. Two ions with the same valence and radius should exchange easily and enter a solid solution in amounts equal to their overall proportions
How does Rb behave? Ni?
therefore some TE's will follow similar major E
Periodic Table is next slide

4. Rb follows K & conc. in Ksp, mica, & late melt
Ni follows Mg & conc in olivine

5. Goldschmidt’s rules
2. If two ions have a similar radius and the same valence: the smaller ion is preferentially incorporated into the solid over the liquid
smaller ion preferentially -> solid (Mg is smaller than Fe so more Mg in Ol than in melt)
Fig Isobaric T-X phase diagram at atmospheric pressure After Bowen and Shairer (1932), Amer. J. Sci. 5th Ser., 24, From Winter (2001) An Introduction to Igneous and Metamorphic Petrology. Prentice Hall.

6. Relative ionic radii for common valences and coordination numbers

7. Ionic charge vs. radius Preference for melt Preference for
mineral phase
Plot of ionic radius vs. ionic charge for
trace elements of geological interest.
Ionic radii are quoted for eight-fold
coordination to allow for comparison
between elements. From Rollinson
(1993).

8. 3. If two ions have a similar radius, but different valence: the ion with the higher charge is preferentially incorporated into the solid over the liquid
(Cr+3 and Ti+4 are always preferred in solids/liquids)

9. Chemical Fractionation
The uneven distribution of an ion between two competing (equilibrium) phases

10. K = equilibrium constant
Exchange equilibrium of a component i between two phases (solid and liquid)
i (liquid) = i (solid)
KD = =
K = equilibrium constant
a solid
a liquid
 X solid
 X liquid i i i i i i

11. Thus if XNi in the system doubles the XNi in all phases will double
Trace element concentrations are in the Henry’s Law region of concentration, so their activity varies in direct relation to their concentration in the system, where [a] = (c)
Thus if XNi in the system doubles the XNi in all phases will double
This does not mean that XNi in all phases is the same, since trace elements do fractionate. Rather the XNi within each phase will vary in proportion to the system concentration
For example: suppose C(Ni) = 20 ppm in a system
C(Ni) in olivine may be 100 ppm
C(Ni) in plagioclase may be 1 ppm
C(Ni) in liquid may be 10 ppm
Double C(Ni) in system to 40 ppm: Ol -> 200 ppm, Plag -> 2 ppm and liquid -> 20 ppm

12. incompatible elements are concentrated in the melt (KD or D) « 1
compatible elements are concentrated in the solid
KD or D » 1
where D is the partition coefficient for any given trace
element between phases; D is a constant for dilute
concentrations of elements

13. For dilute solutions can substitute D for KD: D =
Where CS = the concentration of some element in the solid phase CS CL
Since the concentration of a trace element (unlike major elements--note Fo-Fa) in any phase is proportional to the overall concentration of that element, a more convenient constant is commonly used for them. It is commonly referred to as "D" for TE's (although some authors still use KD) and is called a partition coefficient:
D = C(S)/C(L)
Where CS and CL are the concentration of a trace element in the solid and liquid phases, respectively (the wt% or ppm value directly). As long as the element occurs in very dilute concentrations, D is a constant.

14. Incompatible elements commonly  two subgroups
Smaller, highly charged high field strength (HFS) elements (REE, Th, U, Ce, Pb4+, Zr, Hf, Ti, Nb, Ta)
Low field strength large ion lithophile (LIL) elements (K, Rb, Cs, Ba, Pb2+, Sr, Eu2+) are more mobile, particularly if a fluid phase is involved
Depends on the minerals involved!
Sr -> melt as ol & px separate -> plag (Ca) & not melt if plag is phenocryst phase
Commonly standardized to mantle compositions (olivine, pyroxenes, and perhaps garnet)
Thus the major elements Mg and Fe would usually be referred to as compatible, while K and Na as incompatible

15. High field strength (HFS) elements
Smaller, highly charged

16. Large Ion Lithophiles (LILs)
Low field strength (large ions,
lower charge), more mobile
Rb follows K & conc. in Ksp, mica, & late melt
Ni follows Mg & conc in olivine

17. Compatibility depends on minerals and melts involved.
Which are incompatible? Why?
Not exact, since D varies with the composition of mins & melt

18. For a rock, determine the bulk distribution coefficient D for an element by calculating the contribution for each mineral
Di =  WA DiA
WA = weight % of mineral A in the rock
Di = partition coefficient of element i in mineral A A

19. Note that 85% Ol + Opx, but 5% Grt raises bulk D to 0.366
Example: hypothetical garnet lherzolite = 60% olivine, 25% orthopyroxene, 10% clinopyroxene, and 5% garnet (all by weight), using the data in Table 9-1, is:
DEr = (0.6 · 0.026) + (0.25 · 0.23) + (0.10 · 0.583) + (0.05 · 4.7) = 0.366

20. Trace elements strongly partitioned into a single mineral
Ni - olivine = 14
Figure 9-1a. Ni Harker Diagram for Crater Lake. From data compiled by Rick Conrey. From Winter (2001) An Introduction to Igneous and Metamorphic Petrology. Prentice Hall.

21. Incompatible trace elements concentrate  liquid
Reflect the proportion of liquid at a given state of crystallization or melting
Figure 9-1b. Zr Harker Diagram for Crater Lake. From data compiled by Rick Conrey. From Winter (2001) An Introduction to Igneous and Metamorphic Petrology. Prentice Hall.

22. Trace Element Behavior
The concentration of a major element in a phase is usually buffered by the system, so that it varies little in a phase as the system composition changes
At a given T we could vary Xmelt from 20  60 % Mg/Fe without changing the composition of the melt or the olivine

23. Trace element concentrations are in the Henry’s Law region of concentration, so their activity varies in direct relation to their concentration in the system

24. Trace element concentrations are in the Henry’s Law region of concentration, so their activity varies in direct relation to their concentration in the system
Thus if XNi in the system doubles the XNi in all phases will double

25. Trace element concentrations are in the Henry’s Law region of concentration, so their activity varies in direct relation to their concentration in the system
Thus if XNi in the system doubles the XNi in all phases will double
Because of this, the ratios of trace elements are often superior to the concentration of a single element in identifying the role of a specific mineral

26. K/Rb often used  the importance of amphibole in a source rock
K & Rb behave very similarly, so K/Rb should be ~ constant
If amphibole, almost all K and Rb reside in it
Amphibole has a D of about 1.0 for K and 0.3 for Rb
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

27. Sr and Ba (also incompatible elements)
Sr is excluded from most common minerals except plagioclase
Ba similarly excluded except in alkali feldspar
Ba/Sr will help identify Kspar vs Plag
Both are incompatible -> first partial melts (or residual liquids of FX)
Effect depends on the mineral phases involved
Sr is excluded from most common minerals except plagioclase
Ba similarly excluded except in alkali feldspar
Thus the ratio Ba/Sr increases with crystallization of plagioclase, but may decrease when orthoclase begins to crystallize

28. Compatible example: Ni strongly fractionated  olivine > pyroxene
Cr and Sc  pyroxenes » olivine
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
In all of the above cases using ratios, the idea is to find a mineral with a unique pair of elements for which it alone has a relatively high value of D for one element and a relatively low value of D for the other. The ratio of these elements is then sensitive only to liquid/crystal fractionation associated with that particular mineral

29. Models of Magma Evolution
Batch Melting
The melt remains resident until at some point it is released and moves upward
Equilibrium melting process with variable % melting

30. Models of Magma Evolution
Batch Melting
CL = trace element concentration in the liquid
CO = trace element concentration in the original rock before melting began
F = wt fraction of melt produced = melt/(melt + rock) C 1 Di (1 F) F L O = - +

31. A plot of CL/CO vs. F for various values of Di using the
Batch Melting
A plot of CL/CO vs. F for various values of Di using the
previous equation
Di = 1.0
D = No fractionation so CL/CO = 1 for all values of F
Figure 9-2. Variation in the relative concentration of a trace element in a liquid vs. source rock as a fiunction of D and the fraction melted, using equation (9-5) for equilibrium batch melting. From Winter (2001) An Introduction to Igneous and Metamorphic Petrology. Prentice Hall.

32. Di » 1.0 (compatible element) Very low concentration in melt
Especially for low % melting (low F)
Values of F > 0.4 unlikely for batch melting since greater amounts should separate and rise
Figure 9-2. Variation in the relative concentration of a trace element in a liquid vs. source rock as a fiunction of D and the fraction melted, using equation (9-5) for equilibrium batch melting. From Winter (2001) An Introduction to Igneous and Metamorphic Petrology. Prentice Hall.

33. Highly incompatible elements
• Greatly concentrated in the initial small fraction of melt produced by partial melting
• Subsequently diluted as F increases
Highly incompatible elements are greatly concentrated in the initial small fraction of melt that is produced by partial melting, and subsequently get diluted as F increases
Figure 9-2. Variation in the relative concentration of a trace element in a liquid vs. source rock as a fiunction of D and the fraction melted, using equation (9-5) for equilibrium batch melting. From Winter (2001) An Introduction to Igneous and Metamorphic Petrology. Prentice Hall.

34. As F  1 the concentration of every trace element in the liquid = the source rock (CL/CO 1)Di (1 F) F L O = - +
All -> 1.0 because all of the source is melted
Figure 9-2. Variation in the relative concentration of a trace element in a liquid vs. source rock as a fiunction of D and the fraction melted, using equation (9-5) for equilibrium batch melting. From Winter (2001) An Introduction to Igneous and Metamorphic Petrology. Prentice Hall.

35. C 1 Di (1 F) F L O = - +
As F  0 CL/CO  1/Di
If we know CL of a magma derived by a small degree of batch melting, and we know Di we can estimate the concentration of that element in the source region (CO)
If know (CL) for magma derived by a small degree of batch melting, and we know D, we can estimate the concentration of that element in the source region (CO).
This can provide very valuable information in constraining and characterizing the source region.
Figure 9-2. Variation in the relative concentration of a trace element in a liquid vs. source rock as a fiunction of D and the fraction melted, using equation (9-5) for equilibrium batch melting. From Winter (2001) An Introduction to Igneous and Metamorphic Petrology. Prentice Hall.

36. For very incompatible elements as Di  0 reduces to:1 Di (1 F) F L O = - + C 1 F L O =
If we know the concentration of a very incompatible element in both a magma and the source rock, we can determine the fraction of partial melt produced

37. Worked Example of Batch Melting: Rb and Sr
Basalt with the mode:
1. Convert to weight % minerals (Wol Wcpx etc.)
Table 9-2
. Conversion from mode to
weight percent
Mineral
Mode
Density
Wt prop
Wt% ol 15
3.6 54
0.18
cpx 33
3.4
112.2
0.37
plag 51
2.7
137.7
0.45
Sum
303.9
1.00
Suppose that a source rock with a mode of 51% plagioclase, 33% clinopyroxene, and 18% olivine undergoes batch melting

38. Worked Example of Batch Melting: Rb and Sr
Basalt with the mode:
1. Convert to weight % minerals (Wol Wcpx etc.)
2. Use: Di =  WA Di
and the table of D values for Rb and Sr in each mineral to calculate the bulk distribution coefficients: DRb = and DSr = 0.848
Table 9-2
. Conversion from mode to
weight percent
Mineral
Mode
Density
Wt prop
Wt% ol 15
3.6 54
0.18
cpx 33
3.4
112.2
0.37
plag 51
2.7
137.7
0.45
Sum
303.9
1.00
Rb is incompatible and Sr only slightly so, but near unity

39. 3. Use the batch melting equation to calculate CL/CO
3. Use the batch melting equation to calculate CL/CO for various values of F
Table 9-3
. Batch Fractionation Model for
Rb and Sr C L /C O
= 1/(D(1-F)+F) D Rb Sr F
0.045
0.848
Rb/Sr
0.05
9.35
1.14
8.19
0.1
6.49
1.13
5.73
0.15
4.98
1.12
4.43
0.2
4.03
3.61
0.3
2.92
1.10
2.66
0.4
2.29
1.08
2.11
0.5
1.89
1.07
1.76
0.6
1.60
1.05
1.52
0.7
1.39
1.04
1.34
0.8
1.23
1.03
1.20
0.9
1.01
1.09
From Winter (2001) An Introduction to Igneous and Metamorphic Petrology. Prentice Hall.

40. 4. Plot CL/CO vs. F for each element
Figure 9-3. Change in the concentration of Rb and Sr in the melt derived by progressive batch melting of a basaltic rock consisting of plagioclase, augite, and olivine. From Winter (2001) An Introduction to Igneous and Metamorphic Petrology. Prentice Hall.
Results:
Incompatible element Rb (no K minerals) strongly concentrated in the early small melt proportions (low F)
Thus  a sensitive measure of the progress of fractional crystallization (at least until rock half melted)
As melting proceeds, the incompatible element is gradually diluted by more compatible ones
Since D(Sr) is close to 1.0, the ratio Rb/Sr vs. F is nearly the same as Rb alone
Any ratio of incompatible to compatible element should then be sensitive to the degree of partial melting (at least in the initial stages).
Important for Rb/Sr isotopic systems
Note that can create a series of melts from a single source each with diff Rb/Sr

41. Incremental Batch Melting
Calculate batch melting for successive batches (same equation)
Must recalculate Di as solids change as minerals are selectively melted (computer)

42. Fractional Crystallization
1. Crystals remain in equilibrium with each melt increment
Incremental batch melting in reverse
Equation 9-5 would still apply
Batch FX: F = proportion of liquid remaining

43. Rayleigh fractionation
The other extreme: separation of each crystal as it formed = perfectly continuous fractional crystallization in a magma chamber
Rayleigh: Crystals form and accumulate -> isolated from reaction with the remaining liquid

44. Rayleigh fractionation
The other extreme: separation of each crystal as it formed = perfectly continuous fractional crystallization in a magma chamber
Concentration of some element in the residual liquid, CL is modeled by the Rayleigh equation:
CL/CO = F (D -1) Rayleigh Fractionation
Can also apply the Rayleigh equation to Rayleigh fractional melting

45. Other models are used to analyze
Mixing of magmas
Wall-rock assimilation
Zone refining
Combinations of processes

46. The Rare Earth Elements (REE)
Members of Group IIIA of the Periodic Table La -> to Lutetium (Z = 57  71)
All have very similar chemical and physical properties -> behave as a coherent series
All have a 3+ oxidation state
Ionic radius decreases steadily with increasing atomic number (lanthanide contraction)

47. Contrasts and similarities in the D values: All are incompatible
Also Note:
HREE are less incompatible
Especially in garnet
Eu can  2+ which conc. in plagioclase

48. La Ce Nd Sm Eu Tb Er Dy Yb Lu
REE Diagrams
Plots of concentration as the ordinate (y-axis) against increasing atomic number
Degree of compatibility increases from left to right across the diagram
Concentration
La Ce Nd Sm Eu Tb Er Dy Yb Lu

49. estimates of primordial mantle REE chondrite meteorite concentrations
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
Eliminate Oddo-Harkins effect and make y-scale more functional by normalizing to a standard
estimates of primordial mantle REE
chondrite meteorite concentrations

50. What would an REE diagram look like for an analysis of a chondrite meteorite?
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 ?

51. Divide each element in analysis by the concentration in a chondrite standard
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

52. REE diagrams using batch melting model of a garnet lherzolite for various values of F:
Diagram created in similar way to Rb-Sr diagram in Example Problem
Calculate D(La) for lherzolite and model conc. in melt at F = 0.1 -> point on this diagram for La …
LREE are less compatible than HREE, so melts enriched in LREE -> (-) slopes
Slope is steeper for low values of F (low % partial melting)
As F  1 slope  0 at S/C = 1.0 since all of mantle sample is melted
Note again the use of RATIOS to -> slope on REE
La/Lu ratio -> REE slope
Tb/Lu for HREE only (garnet)
La/Sm -> LREE only
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). From Winter (2001) An Introduction to Igneous and Metamorphic Petrology. Prentice Hall.

53. Europium anomaly when plagioclase is
a fractionating phenocryst or
a residual solid in source
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. REE diagram for 10% batch melting of a hypothetical lherzolite with 20% plagioclase, resulting in a pronounced negative Europium anomaly. From Winter (2001) An Introduction to Igneous and Metamorphic Petrology. Prentice Hall.

54. Spider Diagrams
An extension of the normalized REE technique to a broader spectrum of elements
Chondrite-normalized spider diagrams are commonly organized by (the author’s estimate) of increasing incompatibility L  R
Different estimates  different ordering (poor standardization)
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

55. MORB-normalized Spider
Separates LIL and HFS
MORB-normalization
LIL on left and HFS on right. Incr. incompatibility toward center.
Coherent magma with enrichment has hump shape
Figure 9-7. Ocean island basalt plotted on a mid-ocean ridge basalt (MORB) normalized spider diagram of the type used by Pearce (1983). Data from Sun and McDonough (1989). From Winter (2001) An Introduction to Igneous and Metamorphic Petrology. Prentice Hall.

56. Application of Trace Elements to Igneous Systems
1. Use like major elements on variation diagrams to document FX, assimilation, etc. in a suite of rocks
More sensitive  larger variations as process continues
Figure 9-1a. Ni Harker Diagram for Crater Lake. From data compiled by Rick Conrey. From Winter (2001) An Introduction to Igneous and Metamorphic Petrology. Prentice Hall.

57. 2. Identification of the source rock or a particular mineral involved in either partial melting or fractional crystallization processes
Example: can use REE to distinguish between high pressure and low pressure sources of a mantle-derived magma
In the deep continental crust, and at depths over about 100 km in the mantle, garnet and clinopyroxene are important phases, which remain as residual solids during the generation of up to 15-20% partial melting

58. Garnet concentrates the HREE and fractionates among them
Thus if garnet is in equilibrium with the partial melt (a residual phase in the source left behind) expect a steep (-) slope in REE and HREE
Shallow (< 40 km) partial melting of the mantle will have plagioclase in the resuduum and a Eu anomaly will result

59. Garnet and Plagioclase effect on HREE
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
Garnet and Plagioclase effect on HREE
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

60. Trace elements have much broader general application in petrology than indicating individual mineral involvement
They have been used to indicate mama mixing, assimilation, the degree of partial melting of fractional crystallization, etc.
We will see numerous examples in forthcoming chapters
Figure 9-3. Change in the concentration of Rb and Sr in the melt derived by progressive batch melting of a basaltic rock consisting of plagioclase, augite, and olivine. From Winter (2001) An Introduction to Igneous and Metamorphic Petrology. Prentice Hall.

61. Use as a petrogenetic indicator
Table 9-6 A brief summary of some particularly useful trace elements in igneous petrology
Element
Use as a petrogenetic indicator
Ni, Co, Cr
Highly compatible elements. Ni (and Co) are concentrated in olivine, and Cr in spinel and
clinopyroxene. High concentrations indicate a mantle source.
V, Ti
Both show strong fractionation into Fe-Ti oxides (ilmenite or titanomagnetite). If they behave
differently, Ti probably fractionates into an accessory phase, such as sphene or rutile.
Zr, Hf
Very incompatible elements that do not substitute into major silicate phases (although they may
replace Ti in sphene or rutile).
Ba, Rb
Incompatible element that substitutes for K in K-feldspar, micas, or hornblende. Rb substitutes
less readily in hornblende than K-spar and micas, such that the K/Ba ratio may distinguish these
phases. Sr
Substitutes for Ca in plagioclase (but not in pyroxene), and, to a lesser extent, for K in K-
feldspar. Behaves as a compatible element at low pressure where plagioclase forms early, but
as an incompatible at higher pressure where plagioclase is no longer stable.
REE
Garnet accommodates the HREE more than the LREE, and orthopyroxene and hornblende do
so to a lesser degree. Sphene and plagioclase accommodates more LREE. Eu 2+
is strongly
partitioned into plagioclase. Y
Commonly incompatible (like HREE). Strongly partitioned into garnet and amphibole. Sphene
and apatite also concentrate Y, so the presence of these as accessories could have a
significant effect.
Table 9-6. After Green (1980). Tectonophys., 63, From Winter (2001) An Introduction to Igneous and Metamorphic Petrology. Prentice Hall.

62. Trace elements as a tool to determine paleotectonic environment
Useful for rocks in mobile belts that are no longer recognizably in their original setting
Can trace elements be discriminators of igneous environment?
Approach is empirical on modern occurrences
Concentrate on elements that are immobile during low/medium grade metamorphism
A bit ambiguous, since many variables (country rx, %PM, %FX)
Need immobile TE's, so met has no effect. Ti, Zr, Y, Hf
& apply to basic volc's to eliminate high %FX

63. Figure 9-8. (a) after Pearce and Cann (1973), Earth Planet, Sci. Lett
Figure 9-8. (a) after Pearce and Cann (1973), Earth Planet, Sci. Lett., 19, (b) after Pearce (1982) in Thorpe (ed.), Andesites: Orogenic andesites and related rocks. Wiley. Chichester. pp , Coish et al. (1986), Amer. J. Sci., 286, (c) after Mullen (1983), Earth Planet. Sci. Lett., 62,