trace elements note magnitude of major element changes from winter (2001) an introduction to igneous...

Trace ElementsTrace Elements

Note Note magnitudmagnitude of e of majormajor element element changeschanges

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 From Winter (2001) An Introduction to Igneous and Metamorphic Introduction to Igneous and Metamorphic Petrology. Prentice Hall.Petrology. Prentice Hall.

wt %

wt %

Figure 9-1.Figure 9-1. Harker Diagram for Crater Lake. From data Harker Diagram for Crater Lake. From data compiled by Rick Conrey. From Winter (2001) An Introduction compiled by Rick Conrey. From Winter (2001) An Introduction to Igneous and Metamorphic Petrology. Prentice Hall.to Igneous and Metamorphic Petrology. Prentice Hall.

Note Note magnitudmagnitude of e of tracetrace element element changeschanges

Trace ElementsTrace Elements

ppm

ppm

ppm

ppm

Element DistributionElement DistributionGoldschmidt’s rules (simplistic, but useful)Goldschmidt’s rules (simplistic, but useful)

1.1. Two ions with the same valence and radius Two ions with the same valence and radius should exchange easily and enter a solid should exchange easily and enter a solid solution in amounts equal to their overall solution in amounts equal to their overall proportionsproportions

How does Rb behave? Ni?How does Rb behave? Ni?

Goldschmidt’s rulesGoldschmidt’s rules

2. If two ions have a similar radius and the same 2. If two ions have a similar radius and the same valence: the smaller ion is preferentially incorporated valence: the smaller ion is preferentially incorporated into the solid over the liquidinto the solid over the liquid

Fig. 6-10. Isobaric T-X phase diagram at atmospheric pressure After Bowen and Shairer (1932), Amer. J. Sci. 5th Ser., 24, 177-213. From Winter From Winter (2001) An Introduction to (2001) An Introduction to Igneous and Metamorphic Igneous and Metamorphic Petrology. Prentice Hall.Petrology. Prentice Hall.

Relative ionic radii for common valencesand coordination numbers

Preference forPreference formineral phasemineral phase

PreferencePreferencefor meltfor melt

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).

Ionic chargeIonic chargevs. radiusvs. radius

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

Chemical FractionationChemical Fractionation

The uneven distribution of an ion between The uneven distribution of an ion between two competing (equilibrium) phasestwo competing (equilibrium) phases

Exchange equilibrium of a Exchange equilibrium of a componentcomponent ii between between two two phasesphases (solid and liquid) (solid and liquid)

ii (liquid)(liquid) = = ii (solid)(solid)

KKDD = = = =

K =K = equilibrium constantequilibrium constant

a a solidsolid

a a liquidliquidii

ii

XX solidsolid

XX liquidliquidii

ii

ii

ii

Trace element concentrations are in the Trace element concentrations are in the Henry’s Law region of concentration, so Henry’s Law region of concentration, so their activity varies in direct relation to their their activity varies in direct relation to their concentration in the system, where [a] = (c)concentration in the system, where [a] = (c)

Thus if XThus if XNiNi in the system doubles the X in the system doubles the XNiNi in in

all all phases will doublephases will double This does not mean that XThis does not mean that XNiNi in all phases in all phases

is the same, since trace elements do is the same, since trace elements do fractionate. Rather the Xfractionate. Rather the XNiNi within each within each

phase will vary in proportion to the phase will vary in proportion to the system concentrationsystem concentration

incompatibleincompatible elements are concentrated in the elements are concentrated in the melt melt

(K(KDD or D) « 1 or D) « 1

compatiblecompatible elements are concentrated in the elements are concentrated in the solid solid

KKDD or D » 1 or D » 1

where D is the partition coefficient for any given trace where D is the partition coefficient for any given trace element between phases; D is a constant for dilute element between phases; D is a constant for dilute concentrations of elementsconcentrations of elements

For dilute solutions can substitute D for KFor dilute solutions can substitute D for KDD::

D =D =

Where CWhere CSS = the concentration of some element in = the concentration of some element in

the solid phasethe solid phase

CCSS

CCLL

IncompatibleIncompatible elements commonly elements commonly two subgroups two subgroups

Smaller, highly charged Smaller, highly charged high field strength (HFS)high field strength (HFS) elementselements (REE, Th, U, Ce, Pb(REE, Th, U, Ce, Pb4+4+, Zr, Hf, Ti, Nb, , Zr, Hf, Ti, Nb, Ta)Ta)

Low field strength Low field strength large ion lithophile (LIL)large ion lithophile (LIL) elements elements (K, Rb, Cs, Ba, Pb(K, Rb, Cs, Ba, Pb2+2+, Sr, Eu, Sr, Eu2+2+)) are more are more mobile, particularly if a fluid phase is involvedmobile, particularly if a fluid phase is involved

High field strength (HFS) elementsHigh field strength (HFS) elementsSmaller, highly chargedSmaller, highly charged

Large Ion Lithophiles (LILs)Large Ion Lithophiles (LILs)Low field strength (large ions, Low field strength (large ions, lower charge), more mobilelower charge), more mobile

Table 9-1. Partition Coefficients (CS/CL) for Some Commonly Used Trace

Elements in Basaltic and Andesitic Rocks

Olivine Opx Cpx Garnet Plag Amph MagnetiteRb 0.010 0.022 0.031 0.042 0.071 0.29 Sr 0.014 0.040 0.060 0.012 1.830 0.46 Ba 0.010 0.013 0.026 0.023 0.23 0.42 Ni 14 5 7 0.955 0.01 6.8 29Cr 0.70 10 34 1.345 0.01 2.00 7.4La 0.007 0.03 0.056 0.001 0.148 0.544 2Ce 0.006 0.02 0.092 0.007 0.082 0.843 2Nd 0.006 0.03 0.230 0.026 0.055 1.340 2Sm 0.007 0.05 0.445 0.102 0.039 1.804 1Eu 0.007 0.05 0.474 0.243 0.1/1.5* 1.557 1Dy 0.013 0.15 0.582 1.940 0.023 2.024 1Er 0.026 0.23 0.583 4.700 0.020 1.740 1.5Yb 0.049 0.34 0.542 6.167 0.023 1.642 1.4Lu 0.045 0.42 0.506 6.950 0.019 1.563Data from Rollinson (1993). * Eu3+/Eu2+ Italics are estimated

Rare Earth Elements

Compatibility depends on minerals and melts involved. Compatibility depends on minerals and melts involved.

Which are incompatible? Why?Which are incompatible? Why?

For a For a rock,rock, determine the determine the bulk distribution bulk distribution coefficient Dcoefficient D for an element by calculating for an element by calculating the contribution for each mineralthe contribution for each mineral

DDii = = W WAA D DiAiA

WWAA = weight % of mineral A in the rock = weight % of mineral A in the rock

DDii = partition coefficient of element i in = partition coefficient of element i in

mineral Amineral A

AA

AA

Example: hypothetical garnet lherzolite = 60% olivine, 25% Example: hypothetical garnet lherzolite = 60% olivine, 25% orthopyroxene, 10% clinopyroxene, and 5% garnet (all by orthopyroxene, 10% clinopyroxene, and 5% garnet (all by weightweight), ), using the data in Table 9-1, is:using the data in Table 9-1, is:

DDErEr = (0.6 · 0.026) + (0.25 · 0.23) + (0.10 · 0.583) + (0.05 · 4.7) = = (0.6 · 0.026) + (0.25 · 0.23) + (0.10 · 0.583) + (0.05 · 4.7) =

0.3660.366




Rare Earth Elements

Trace elements strongly partitioned into a single mineralTrace elements strongly partitioned into a single mineral Ni - olivine = 14Ni - olivine = 14

Figure 9-1a.Figure 9-1a. Ni Harker Diagram for Crater Lake. From data compiled by Rick Conrey. From Ni Harker Diagram for Crater Lake. From data compiled by Rick Conrey. From Winter (2001) An Introduction to Igneous and Metamorphic Petrology. Prentice Hall.Winter (2001) An Introduction to Igneous and Metamorphic Petrology. Prentice Hall.

Incompatible trace elements concentrate Incompatible trace elements concentrate liquid liquid

Reflect the proportion of liquid at a given state of Reflect the proportion of liquid at a given state of crystallization or meltingcrystallization or melting

Figure 9-1b.Figure 9-1b. Zr Harker Diagram for Crater Lake. From data compiled by Rick Conrey. Zr Harker Diagram for Crater Lake. From data compiled by Rick Conrey. From Winter (2001) An Introduction to Igneous and Metamorphic Petrology. Prentice Hall.From Winter (2001) An Introduction to Igneous and Metamorphic Petrology. Prentice Hall.

Trace Element BehaviorTrace Element Behavior The concentration of a The concentration of a majormajor element in a phase is element in a phase is

usually buffered by the system, so that it varies usually buffered by the system, so that it varies little in a phase as the system composition changeslittle in a phase as the system composition changes

At a given T we could vary At a given T we could vary XXmeltmelt from 20 from 20 60 % 60 % Mg/Fe without changing the Mg/Fe without changing the composition of the melt or composition of the melt or the olivinethe olivine

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

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

Thus if XThus if XNiNi in the system doubles the X in the system doubles the XNiNi in all in all

phases will doublephases will double

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

Thus if XThus if XNiNi in the system doubles the X in the system doubles the XNiNi in all in all

phases will doublephases will double

Because of this, the Because of this, the ratiosratios of trace elements of trace elements are often superior to the concentration of a are often superior to the concentration of a single element in identifying the role of a single element in identifying the role of a specific mineralspecific mineral

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




Rare Earth Elements

Sr and Ba (also Sr and Ba (also incompatibleincompatible elements) elements) SrSr is excluded from most common minerals is excluded from most common minerals

except except plagioclaseplagioclase BaBa similarly excluded except in similarly excluded except in alkali feldsparalkali feldspar




Rare Earth Elements

CompatibleCompatible example: example: NiNi strongly fractionated strongly fractionated olivineolivine > pyroxene > pyroxene CrCr and and ScSc pyroxenespyroxenes » olivine » olivine Ni/Cr or Ni/Sc can distinguish the effects of olivine Ni/Cr or Ni/Sc can distinguish the effects of olivine

and augite in a partial melt or a suite of rocks and augite in a partial melt or a suite of rocks produced by fractional crystallizationproduced by fractional crystallization

Models of Magma EvolutionModels of Magma Evolution Batch MeltingBatch Melting

The melt remains resident until at some point it is The melt remains resident until at some point it is released and moves upwardreleased and moves upward

Equilibrium melting process with variable % Equilibrium melting process with variable % meltingmelting

Models of Magma EvolutionModels of Magma Evolution Batch MeltingBatch Melting

CCLL = trace element concentration in the liquid = trace element concentration in the liquid

CCOO = trace element concentration in the original rock = trace element concentration in the original rock

before melting beganbefore melting began

F = wt fraction of melt F = wt fraction of melt producedproduced = melt/(melt + rock) = melt/(melt + rock)

CCCC

11DDii(1(1 F)F) FF

LL

OO

Batch MeltingBatch Melting

A plot of CA plot of CLL/C/COO vs. F for various vs. F for various

values of Dvalues of Dii using the using the

previous equationprevious equation DDii = 1.0 = 1.0

Figure 9-2.Figure 9-2. Variation in the relative concentration of a Variation in the relative concentration of a trace element in a liquid vs. source rock as a fiunction trace element in a liquid vs. source rock as a fiunction of D and the fraction melted, using equation (9-5) for of D and the fraction melted, using equation (9-5) for equilibrium batch melting. From Winter (2001) An equilibrium batch melting. From Winter (2001) An Introduction to Igneous and Metamorphic Petrology. Introduction to Igneous and Metamorphic Petrology. Prentice Hall.Prentice Hall.

DDii » 1.0 ( » 1.0 (compatible compatible element)element)

Very low concentration in Very low concentration in meltmelt

Especially for low % Especially for low % melting (low F)melting (low F)


Highly Highly incompatibleincompatible elements elements

• • Greatly concentrated in the Greatly concentrated in the initial small fraction of melt initial small fraction of melt produced by partial meltingproduced by partial melting

• • Subsequently diluted as F Subsequently diluted as F increasesincreases


As F As F 1 the concentration of 1 the concentration of everyevery trace element in the liquid trace element in the liquid = the source rock (C= the source rock (CLL/C/COO 1) 1)

As F As F 11

CCLL/C/COO

1 1

CC

1Di (1 F) F

L

O


As F As F 0 0 CCLL/C/COO 1/D 1/Dii

If we know CIf we know CLL of a magma derived of a magma derived

by a small degree of batch melting, by a small degree of batch melting, and we know Dand we know Dii we can estimate we can estimate

the concentration of that element the concentration of that element in the source region (Cin the source region (COO))

CC

1Di (1 F) F

L

O


For very For very incompatibleincompatible elements as D elements as Dii 0 0

reduces reduces to:to:

C

C

1

FL

O

CC

1Di (1 F) F

L

O

If we know the concentration of a very If we know the concentration of a very incompatible element in both a magma and the incompatible element in both a magma and the source rock, we can determine the fraction of source rock, we can determine the fraction of partial melt producedpartial melt produced

Worked Example of Batch Melting: Worked Example of Batch Melting: Rb and Rb and SrSrBasalt with the mode:Basalt with the mode:

1.1. Convert to Convert to weightweight % minerals (W % minerals (Wolol W Wcpxcpx etc.) 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

Worked Example of Batch Melting: Worked Example of Batch Melting: Rb and Rb and SrSr

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

Basalt with the mode:Basalt with the mode:

1.1. Convert to Convert to weightweight % minerals (W % minerals (Wolol W Wcpxcpx etc.) etc.)

2.2. Use: Use: DDii = = W WAA D Dii

and the table of D values for Rb and Sr in each mineral and the table of D values for Rb and Sr in each mineral to calculate the bulk distribution coefficients: Dto calculate the bulk distribution coefficients: DRbRb = =

0.045 and D0.045 and DSrSr = 0.848 = 0.848

Table 9-3 . Batch Fractionation Model for Rb and Sr

CL/CO = 1/(D(1-F)+F)

DRb DSr

F 0.045 0.848 Rb/Sr0.05 9.35 1.14 8.190.1 6.49 1.13 5.730.15 4.98 1.12 4.430.2 4.03 1.12 3.610.3 2.92 1.10 2.660.4 2.29 1.08 2.110.5 1.89 1.07 1.760.6 1.60 1.05 1.520.7 1.39 1.04 1.340.8 1.23 1.03 1.200.9 1.10 1.01 1.09

3.3. Use the batch melting equation to calculate C Use the batch melting equation to calculate CLL/C/COO

for various values of Ffor various values of F

From Winter (2001) An Introduction to Igneous and Metamorphic Petrology. Prentice Hall.From Winter (2001) An Introduction to Igneous and Metamorphic Petrology. Prentice Hall.

4.4. Plot C Plot CLL/C/COO vs. F for each element vs. F for each element

Figure 9-3.Figure 9-3. Change in the concentration Change in the concentration of Rb and Sr in the melt derived by of Rb and Sr in the melt derived by progressive batch melting of a basaltic progressive batch melting of a basaltic rock consisting of plagioclase, augite, rock consisting of plagioclase, augite, and olivine. From Winter (2001) An and olivine. From Winter (2001) An Introduction to Igneous and Introduction to Igneous and Metamorphic Petrology. Prentice Hall.Metamorphic Petrology. Prentice Hall.

Incremental Batch MeltingIncremental Batch Melting

Calculate batch melting for successive Calculate batch melting for successive batches (same equation)batches (same equation)

Must recalculate DMust recalculate Dii as solids change as as solids change as

minerals are minerals are selectivelyselectively melted (computer) melted (computer)

Fractional CrystallizationFractional Crystallization1. Crystals remain in equilibrium with each 1. Crystals remain in equilibrium with each

melt incrementmelt increment

Rayleigh fractionationRayleigh fractionation The other extreme: separation of each The other extreme: separation of each

crystal as it formed = perfectly continuous crystal as it formed = perfectly continuous fractional crystallization in a magma fractional crystallization in a magma chamberchamber

Rayleigh fractionationRayleigh fractionation

The other extreme: separation of each The other extreme: separation of each crystal as it formed = perfectly continuous crystal as it formed = perfectly continuous fractional crystallization in a magma fractional crystallization in a magma chamber chamber Concentration of some element in the Concentration of some element in the residualresidual

liquid, Cliquid, CLL is modeled by the Rayleigh equation: is modeled by the Rayleigh equation:

CCLL/C/COO = F = F (D -1)(D -1) Rayleigh FractionationRayleigh Fractionation

Other models are used to analyzeOther models are used to analyze Mixing of magmasMixing of magmas Wall-rock assimilationWall-rock assimilation Zone refiningZone refining Combinations of processes Combinations of processes

The Rare Earth Elements (REE)The Rare Earth Elements (REE)

Contrasts and similarities in the D values:Contrasts and similarities in the D values:

All are incompatibleAll are incompatibleTable 9-1 . Partition Coefficients for some commonly used

trace elements in basaltic and andesitic rocks Bulk D calculation

Olivine Opx Cpx Garnet Plag Amph

Rb 0.006 0.02 0.04 0.001 0.1 0.3

Sr 0.01 0.01 0.14 0.001 1.8 0.57

Ba 0.006 0.12 0.07 0.002 0.23 0.31

Ni 14 5 2.6 0.4 0.01 3

Cr 2.1 10 8.4 0.17 10 1.6

La 0.007 0.02 0.08 0.05 0.14 0.27

Ce 0.009 0.02 0.34 0.05 0.14 0.34

Nd 0.009 0.05 0.6 0.07 0.08 0.19

Sm 0.009 0.05 0.9 0.06 0.08 0.91

Eu 0.008 0.05 0.9 0.9 0.1/1.5* 1.01

Tb 0.01 0.05 1 5.6 0.03 1.4

Er 0.013 0.31 1 18 0.08 0.48

Yb 0.014 0.34 0.2 30 0.07 0.97

Lu 0.016 0.11 0.82 35 0.08 0.89

data from Henderson (1982) * Eu3+/Eu2+ Italics are estimated

Rare Earth Elements

Also Note:Also Note:

HREEHREE are less are less incompatibleincompatible

Especially in Especially in garnetgarnet

EuEu can can 2+ 2+ which conc. which conc. in in plagioclaseplagioclase

REE DiagramsREE DiagramsPlots of concentration as the ordinate (y-axis) Plots of concentration as the ordinate (y-axis)

against increasing atomic numberagainst increasing atomic number Degree of compatibility increases from left Degree of compatibility increases from left

to right across the diagramto right across the diagram

Con

cent

rati

onC

once

ntra

tion

La Ce Nd Sm Eu Tb Er Dy Yb LuLa Ce Nd Sm Eu Tb Er Dy Yb Lu

-3

-2

-1

0

1

2

3

4

5

6

7

8

9

10

11

0 10 20 30 40 50 60 70 80 90 100

Atomic Number (Z)

Log (Abundance in CI Chondritic Meteorite)

HHe

Li

Be

B

C

N

O

F

Sc

Fe

Ni

Ne MgSi

SCa

Ar

Ti

PbPtSn Ba

VK

NaAlP

Cl

ThU

Eliminate Eliminate Oddo-Harkins effectOddo-Harkins effect and make y-scale more and make y-scale more functional by normalizing to a standardfunctional by normalizing to a standard

estimates of primordial mantle REEestimates of primordial mantle REE chondrite meteorite concentrationschondrite meteorite concentrations

What would an REE diagram look What would an REE diagram look like for an analysis of a chondrite like for an analysis of a chondrite

meteorite?meteorite?

0.00

2.00

4.00

6.00

8.00

10.00

56 58 60 62 64 66 68 70 72

sam

ple

/ch

on

dri

te

L La Ce Nd Sm Eu Tb Er Yb Lu

?

Divide each element in analysis by the Divide each element in analysis by the concentration in a chondrite standardconcentration 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

sam

ple

/ch

on

dri

te

L La Ce Nd Sm Eu Tb Er Yb Lu

REE diagrams using batch melting model of REE diagrams using batch melting model of a garnet lherzolite for various values of F:a garnet lherzolite for various values of F:

Figure 9-4.Figure 9-4. Rare Earth Rare Earth concentrations (normalized to concentrations (normalized to chondrite) for melts produced at chondrite) for melts produced at various values of F via melting of a various values of F via melting of a hypothetical garnet lherzolite using hypothetical garnet lherzolite using the batch melting model (equation the batch melting model (equation 9-5). From Winter (2001) An 9-5). From Winter (2001) An Introduction to Igneous and Introduction to Igneous and Metamorphic Petrology. Prentice Metamorphic Petrology. Prentice Hall.Hall.

Europium anomalyEuropium anomaly when plagioclase is when plagioclase is a fractionating phenocrysta fractionating phenocryst

oror a residual solid in sourcea residual solid in source

Figure 9-5.Figure 9-5. REE diagram for 10% REE diagram for 10% batch melting of a hypothetical batch melting of a hypothetical lherzolite with 20% plagioclase, lherzolite with 20% plagioclase, resulting in a pronounced negative resulting in a pronounced negative Europium anomaly. From Winter Europium anomaly. From Winter (2001) An Introduction to Igneous (2001) An Introduction to Igneous and Metamorphic Petrology. and Metamorphic Petrology. Prentice Hall.Prentice Hall.

Spider DiagramsSpider DiagramsAn extension of the normalized REE An extension of the normalized REE technique to a broader spectrum of elementstechnique to a broader spectrum of elements

Fig. 9-6. 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.

Chondrite-normalized spider Chondrite-normalized spider diagrams are commonly diagrams are commonly organized by (the author’s organized by (the author’s estimate) of increasing estimate) of increasing incompatibility L incompatibility L R R

Different estimates Different estimates different ordering (poor different ordering (poor standardization)standardization)

MORB-normalized Spider MORB-normalized Spider Separates LIL and HFSSeparates LIL and HFS

Figure 9-7.Figure 9-7. Ocean island basalt Ocean island basalt plotted on a mid-ocean ridge plotted on a mid-ocean ridge basalt (MORB) normalized basalt (MORB) normalized spider diagram of the type used spider diagram of the type used by Pearce (1983). Data from by Pearce (1983). Data from Sun and McDonough (1989). Sun and McDonough (1989). From Winter (2001) An From Winter (2001) An Introduction to Igneous and Introduction to Igneous and Metamorphic Petrology. Metamorphic Petrology. Prentice Hall.Prentice Hall.

Application of Trace Elements to Igneous Systems

1. Use like major elements on variation diagrams to 1. Use like major elements on variation diagrams to document FX, assimilation, etc. in a suite of rocksdocument FX, assimilation, etc. in a suite of rocks More sensitive More sensitive larger variations as process larger variations as process

continuescontinues

Figure 9-1a.Figure 9-1a. Ni Harker Diagram for Ni Harker Diagram for Crater Lake. From data compiled by Crater Lake. From data compiled by Rick Conrey. From Winter (2001) An Rick Conrey. From Winter (2001) An Introduction to Igneous and Introduction to Igneous and Metamorphic Petrology. Prentice Metamorphic Petrology. Prentice Hall.Hall.

2. Identification of the source rock or a particular 2. Identification of the source rock or a particular mineral involved in either partial melting or mineral involved in either partial melting or fractional crystallization processesfractional crystallization processes

Table 9-1 . Partition Coefficients for some commonly used trace elements in basaltic and andesitic rocks Bulk D calculation

Olivine Opx Cpx Garnet Plag Amph

Rb 0.006 0.02 0.04 0.001 0.1 0.3

Sr 0.01 0.01 0.14 0.001 1.8 0.57

Ba 0.006 0.12 0.07 0.002 0.23 0.31

Ni 14 5 2.6 0.4 0.01 3

Cr 2.1 10 8.4 0.17 10 1.6

La 0.007 0.02 0.08 0.05 0.14 0.27

Ce 0.009 0.02 0.34 0.05 0.14 0.34

Nd 0.009 0.05 0.6 0.07 0.08 0.19

Sm 0.009 0.05 0.9 0.06 0.08 0.91

Eu 0.008 0.05 0.9 0.9 0.1/1.5* 1.01

Tb 0.01 0.05 1 5.6 0.03 1.4

Er 0.013 0.31 1 18 0.08 0.48

Yb 0.014 0.34 0.2 30 0.07 0.97

Lu 0.016 0.11 0.82 35 0.08 0.89

data from Henderson (1982) * Eu3+/Eu2+ Italics are estimated

Rare Earth Elements

GarnetGarnet concentrates the HREE and fractionates among them concentrates the HREE and fractionates among them

Thus if garnet is in equilibrium with the partial melt (a residual Thus if garnet is in equilibrium with the partial melt (a residual phase in the source left behind) expect a steep (-) slope in REE phase in the source left behind) expect a steep (-) slope in REE and and HREEHREE

Shallow (< 40 Shallow (< 40 km) partial km) partial melting of the melting of the mantle will have mantle will have plagioclaseplagioclase in in the resuduum the resuduum and a Eu and a Eu anomaly will anomaly will resultresult

0.00

2.00

4.00

6.00

8.00

10.00

56 58 60 62 64 66 68 70 72

sa

mp

le/c

ho

nd

rite

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

56 58 60 62 64 66 68 70 72

sa

mp

le/c

ho

nd

rite


57% Ol 14% Opx 14% Cpx 14% Grt

Garnet and Plagioclase effect on HREE

0.00

2.00

4.00

6.00

8.00

10.00

sam

ple

/ch

on

dri

te

60% Ol 15% Opx 15% Cpx 10%Plag


Figure 9-3.Figure 9-3. Change in the concentration Change in the concentration of Rb and Sr in the melt derived by of Rb and Sr in the melt derived by progressive batch melting of a basaltic progressive batch melting of a basaltic rock consisting of plagioclase, augite, rock consisting of plagioclase, augite, and olivine. From Winter (2001) An and olivine. From Winter (2001) An Introduction to Igneous and Introduction to Igneous and Metamorphic Petrology. Prentice Hall.Metamorphic Petrology. Prentice Hall.

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 andclinopyroxene. High concentrations indicate a mantle source.

V, Ti Both show strong fractionation into Fe-Ti oxides (ilmenite or titanomagnetite). If they behavedifferently, 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 mayreplace Ti in sphene or rutile).

Ba, Rb Incompatible element that substitutes for K in K-feldspar, micas, or hornblende. Rb substitutesless readily in hornblende than K-spar and micas, such that the K/Ba ratio may distinguish thesephases.

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, butas an incompatible at higher pressure where plagioclase is no longer stable.

REE Garnet accommodates the HREE more than the LREE, and orthopyroxene and hornblende doso to a lesser degree. Sphene and plagioclase accommodates more LREE. Eu2+

is stronglypartitioned into plagioclase.

Y Commonly incompatible (like HREE). Strongly partitioned into garnet and amphibole. Spheneand apatite also concentrate Y, so the presence of these as accessories could have asignificant effect.

Table 9-6.Table 9-6. After Green (1980). Tectonophys., After Green (1980). Tectonophys., 6363, 367-385. From Winter (2001) An Introduction to Igneous , 367-385. From Winter (2001) An Introduction to Igneous and Metamorphic Petrology. Prentice Hall.and Metamorphic Petrology. Prentice Hall.

Trace elements as a tool to Trace elements as a tool to determine paleotectonic determine paleotectonic

environmentenvironment Useful for rocks in mobile belts that are no Useful for rocks in mobile belts that are no

longer recognizably in their original settinglonger recognizably in their original setting Can trace elements be discriminators of Can trace elements be discriminators of

igneous environment?igneous environment? Approach is Approach is empiricalempirical on on modernmodern occurrences occurrences Concentrate on elements that are immobile Concentrate on elements that are immobile

during low/medium grade metamorphismduring low/medium grade metamorphism

Figure 9-8.Figure 9-8. (a)(a) after Pearce and Cann (1973), after Pearce and Cann (1973), Earth Planet, Sci. Lett., Earth Planet, Sci. Lett., 1919, 290-300, 290-300. . (b)(b) after Pearce (1982) after Pearce (1982) in Thorpe (ed.), in Thorpe (ed.), Andesites: Orogenic andesites and related rocks. Wiley. Chichester. pp. 525-548Andesites: Orogenic andesites and related rocks. Wiley. Chichester. pp. 525-548 , Coish et al. (1986), , Coish et al. (1986), Amer. J. Sci., Amer. J. Sci., 286286, 1-28, 1-28.. (c)(c) after Mullen (1983), after Mullen (1983), Earth Planet. Sci. Lett., Earth Planet. Sci. Lett., 6262, 53-62., 53-62.

trace elements note magnitude of major element changes from winter (2001) an introduction to igneous...

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