Chapter 9: Trace Elements Chapter 9: Trace Elements

Chapter 9: Trace Elements Chapter 9: Trace Elements

Note small magnitude Note small magnitude of major element

of major element changes. However changes. However (next slide) …

(next slide) …

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.

Please bring to the Field Trip on Saturday a color copy of

http://www.kean.edu/~csmart/Petr ology/Lectures/Field%20Trip%201%

20Maps.pptx

Transition Elements Transition Elements

Transition elements often vary by > 10

wrt SiO

. Very useful since so

sensitive to distribution &

fractionation

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.

Zr, a transition element Incompatible HFSE

See slide 43

Goldschmidt’s rules Goldschmidt’s rules

(simplistic, but useful) (simplistic, but useful)

1. 1. 2 ions with the same valence and radius 2 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 proportions

proportions

How does Rb

How does Rb

behave? As K behave? As K

, ,

concentrated in K-spars, micas, and evolved concentrated in K-spars, micas, and evolved melts

melts

Ni Ni

behaves as Mg behaves as Mg

, concentrates in Olivine , concentrates in Olivine

TAKE OUT YOUR COORDINATION NUMBERS AND IONIC RADII CHART

Rb⁺ [6] 1.57 Å follows K⁺ [6] 1.46 Å &

conc. in K-Spar, mica, & late melt.

Ni⁺⁺ [6] 0.77 Å follows Mg⁺⁺ [6] 0.8 Å

& conc in Mg-Olivine “Forsterite”

Goldschmidt’s rules Goldschmidt’s rules

2. If 2 ions have a similar radius and the same valence:

2. If 2 ions have a similar radius and the same valence:

the smaller ion is preferentially incorporated into the the smaller ion is preferentially incorporated into the

solid over the liquid 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.

Smaller ion

preferentially -> solid (Mg⁺⁺ is smaller than Fe⁺⁺ so more Mg⁺⁺ in high temp Olivine than in melt)

Bounces off the rim less

3. If 2 ions have a similar radius, but different If 2 ions have a similar radius, but different valence: the ion with the higher charge is valence: the ion with the higher charge is

preferentially incorporated into the solid preferentially incorporated into the solid

over the liquid over the liquid

Example Ti

[6] r=0.69 Angstrom Other ions this size Fe

r=0.68 A Mn

[6] r=.70 A

Ti

is always preferred in solids over liquids.

Example Cr

[6] r=0.76

Other ions this size Ni

[6] r=0.77 A Fe

[6] r=.77

Cr

is always preferred in solids over liquids.

1 Ångström = 1.0 × 10

meters

Rutile TiO

versus

Hematite Fe

O

Chemical Fractionation Chemical Fractionation



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

two competing (equilibrium) phases



Example: the ratio of Ca Example: the ratio of Ca

/Na /Na

is always is always greater in plagioclase crystals than in the greater in plagioclase crystals than in the

coexisting melt. Ca

coexisting melt. Ca

higher valance than higher valance than Na Na

, goes into Plag xtals. first. , goes into Plag xtals. first.

If melting Plag, Na+ goes to melt first. If melting Plag, Na+ goes to melt first.



Example: the ratio of Mg Example: the ratio of Mg

/Fe /Fe

is always is always greater in Olivine than in the coexisting greater in Olivine than in the coexisting

melt.

melt.

Anorthite higher T than Albite

Forsterite higher T than Fayalite

If the reaction between solid and liquid phases is a If the reaction between solid and liquid phases is a

phase change of some component i phase change of some component i

i i _{(liquid) (liquid)}   i i _{(solid) (solid)}

A distribution constant K

is

Where X

is the mole fraction of component i in some phase. mole fraction K

the ratio of solubility of component i in these two phases.

Recall that we

used the lever

principle to

estimate this

ratio from our

phase diagrams

As long as the concentrations of the components are dilute, call K

the partition coefficient

Where C is the concentration of a trace element in the phase indicated, solid and liquid, in ppm or wt%

Table 9.1 (three slides below this) gives partition coefficients for commonly used trace elements in minerals precipitating from basaltic or andesitic melts.

Different units

 Trace element activity varies in direct relation to their concentration in the system.

 Thus if for Nickel X

in the system doubles the X

in all phases will double

– This does not mean that X

in all phases is the same, since trace elements do

fractionate. Rather the X

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

 Incompatible elements concentrate in the Incompatible elements concentrate in the melt

melt

K K

« 1 much less than 1 « 1 much less than 1

Lesson: incompatibles don’t stick on crystal faces unless the Lesson: incompatibles don’t stick on crystal faces unless the

Temps are low. Melt a xtal, incompatibles go to the melt.

Temps are low. Melt a xtal, incompatibles go to the melt.

 Compatible elements concentrate in the Compatible elements concentrate in the solid

solid

K K

» 1 much more than 1 » 1 much more than 1

Compatibility depends on minerals and melts involved.

Compatibility depends on minerals and melts involved.

Which are incompatible? K

Which are incompatible? K

<< 1 , in liquid melt << 1 , in liquid melt

I marked some

extreme

examples

 For a rock, determine the bulk distribution For a rock, determine the bulk distribution

coefficient D for an element by calculating the coefficient D for an element by calculating the

contribution for each mineral contribution for each mineral

eq. 9-4: D

eq. 9-4: D

= =   W W

D D

W W

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

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

mineral A mineral A

AA

AA

Garnet Lherzolite Garnet Lherzolite

Mantle Xenolith (Garnet Lherzolite) Kimberley, SOUTH AFRICA

Photographed by Tony Peterson

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 weight weight ), ),

using the data in Table 9-1, the bulk distribution coefficient D for Er is:

using the data in Table 9-1, the bulk distribution coefficient D for Er is:

DD_ErEr = (0.6 · 0.026) + (0.25 · 0.23) + (0.10 · 0.583) + (0.05 · 4.7) = 0.366 = (0.6 · 0.026) + (0.25 · 0.23) + (0.10 · 0.583) + (0.05 · 4.7) = 0.366

Table 9-1. Partition Coefficients (CS/CL) for Some Commonly Used Trace Elements in Basaltic and Andesitic Rocks

Olivine Opx Cpx Garnet Plag Amph Magnetite

Rb 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 29

Cr 0.70 10 34 1.345 0.01 2.00 7.4

La 0.007 0.03 0.056 0.001 0.148 0.544 2

Ce 0.006 0.02 0.092 0.007 0.082 0.843 2

Nd 0.006 0.03 0.230 0.026 0.055 1.340 2

Sm 0.007 0.05 0.445 0.102 0.039 1.804 1

Eu 0.007 0.05 0.474 0.243 0.1/1.5* 1.557 1

Dy 0.013 0.15 0.582 1.940 0.023 2.024 1

Er 0.026 0.23 0.583 4.700 0.020 1.740 1.5

Yb 0.049 0.34 0.542 6.167 0.023 1.642 1.4

Lu 0.045 0.42 0.506 6.950 0.019 1.563

Data from Rollinson (1993). * Eu³⁺/Eu²⁺ Italics are estimated

Rare Earth Elements

http://earthref.or g/KDD/e:68/

Er = Erbium

 Coef. D for Ni in Olivine in Tb 9-1 = 14>>1 Coef. D for Ni in Olivine in Tb 9-1 = 14>>1

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.

Nippm

We mentioned earlier

Transition elements often vary by > 10

wrt SiO2. Very useful since so sensitive to distribution & fractionation

The abrupt drop in Ni below 55% SiO2

indicates fractionation

of Olivine there. At

SiO2 > 55% another

mineral or process is

removing Ni



Incompatible trace elements D<< 1 concentrate Incompatible trace elements D<< 1 concentrate in the in the liquid until the melt cools, which is when it has more liquid until the melt cools, which is when it has more

silica. So Trace Elements reflect the proportion of silica. So Trace Elements reflect the proportion of liquid at a given state of crystallization or melting liquid at a given state of crystallization 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.

Zrppm

Zr, a transition element Incompatible HFSE

See slide 43

Trace element concentrations are in the Trace element concentrations are in the Henry’s Law* region of concentration, Henry’s Law* region of concentration,

so their activity varies in direct relation so their activity varies in direct relation

to their concentration in the system to their concentration in the system Thus if X

Thus if X

in the system doubles the X in the system doubles the X

in in all phases will double

all phases will double Because of this, the

Because of this, the ratios ratios of trace _{of trace} elements are often superior to the elements are often superior to the

concentration of a single element in concentration of a single element in

identifying the role of a specific mineral identifying the role of a specific mineral

* "At a constant temperature, the amount of a given gas that dissolves in a given type and volume of liquid is directly proportional to the partial pressure of that gas in

equilibrium with that liquid."



K/Rb often used to measure the importance of K/Rb often used to measure the importance of amphibole amphibole

in a source rock in a source rock

– K & Rb behave very similarly, so K/Rb should be ~ K & Rb behave very similarly, so K/Rb should be ~ constant

constant

– If amphibole important, almost all K and Rb reside in it If amphibole important, almost all K and Rb reside in it – Amphibole has a D of about 1.0 for K and 0.3 for Rb Amphibole has a D of about 1.0 for K and 0.3 for Rb

Table 9-1. Partition Coefficients (CS/CL) for Some Commonly Used Trace Elements in Basaltic and Andesitic Rocks

Olivine Opx Cpx Garnet Plag Amph Magnetite

Rb 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 29

Cr 0.70 10 34 1.345 0.01 2.00 7.4

La 0.007 0.03 0.056 0.001 0.148 0.544 2

Ce 0.006 0.02 0.092 0.007 0.082 0.843 2

Nd 0.006 0.03 0.230 0.026 0.055 1.340 2

Sm 0.007 0.05 0.445 0.102 0.039 1.804 1

Eu 0.007 0.05 0.474 0.243 0.1/1.5* 1.557 1

Dy 0.013 0.15 0.582 1.940 0.023 2.024 1

Er 0.026 0.23 0.583 4.700 0.020 1.740 1.5

Yb 0.049 0.34 0.542 6.167 0.023 1.642 1.4

Lu 0.045 0.42 0.506 6.950 0.019 1.563

Data from Rollinson (1993). * Eu³⁺/Eu²⁺ Italics are estimated

Rare Earth Elements

 Sr and Ba (also incompatible elements) Sr and Ba (also incompatible elements)

 Sr is excluded from most common minerals Sr is excluded from most common minerals except plagioclase

except plagioclase

 Ba similarly excluded except in alkali Ba similarly excluded except in alkali

feldspar (Sanidine, Orthoclase, Microcline) feldspar (Sanidine, Orthoclase, Microcline)

 ratio Ba/Sr increases w plagioclase, ratio Ba/Sr increases w plagioclase,

decreases when orthoclase xtals present decreases when orthoclase xtals present

Table 9-1. Partition Coefficients (CS/CL) for Some Commonly Used Trace Elements in Basaltic and Andesitic Rocks

Olivine Opx Cpx Garnet Plag Amph Magnetite

Rb 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 29

Cr 0.70 10 34 1.345 0.01 2.00 7.4

La 0.007 0.03 0.056 0.001 0.148 0.544 2

Ce 0.006 0.02 0.092 0.007 0.082 0.843 2

Nd 0.006 0.03 0.230 0.026 0.055 1.340 2

Sm 0.007 0.05 0.445 0.102 0.039 1.804 1

Eu 0.007 0.05 0.474 0.243 0.1/1.5* 1.557 1

Dy 0.013 0.15 0.582 1.940 0.023 2.024 1

Er 0.026 0.23 0.583 4.700 0.020 1.740 1.5

Yb 0.049 0.34 0.542 6.167 0.023 1.642 1.4

Lu 0.045 0.42 0.506 6.950 0.019 1.563

Data from Rollinson (1993). * Eu³⁺/Eu²⁺ Italics are estimated

Rare Earth Elements

Compatible example:

Compatible example:

 Ni strongly fractionated (goes to solids) from olivines Ni strongly fractionated (goes to solids) from olivines to pyroxenes

to pyroxenes

 Cr and Sc Cr and Sc   pyroxenes > olivine pyroxenes > 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 crystallization

produced by fractional crystallization

Sc Scandium element 21

Models of Magma Evolution Models of Magma Evolution



Batch Melting Batch Melting



The melt remains in equilibrium with the solid until The melt remains in equilibrium with the solid until at some point it floats upward, separating from the at some point it floats upward, separating from the

solids

solids

Models of Magma Evolution Models of Magma Evolution

 Batch Melting Batch Melting (Shaw) (Shaw) eq. 9-5

eq. 9-5

C C

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

C C

= trace element concentration in the original = trace element concentration in the original rock before melting began

rock before melting began F = wt fraction of melt

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

rock)

D D

= bulk distribution coefficient for element i = bulk distribution coefficient for element i

C C

C C 1 1

D D

(1 (1 F) F) F F

LL OO

 

   

Batch Melting Batch Melting

A plot of C

A plot of C

/C /C

vs. F for vs. F for various values of D

various values of D

using using eq. 9-5

eq. 9-5 For D

For D

= 1.0 there is = 1.0 there is (by (by definition)

definition) no fractionation, no fractionation, concentration of element i concentration of element i the same in solid and liquid the same in solid and liquid

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.

Unlikely F values

low D = incompatible low F little partial melting

no fractionation

– Especially true for low % melting Especially true for low % melting (low F) and D

(low F) and D

<< 1.0 << 1.0

(= (= incompatible incompatible element) element)

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 function trace element in a liquid vs. source rock as a function 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.

The concentration of the trace element in the The concentration of the trace element in the

liquid varies more as D

liquid varies more as D

deviates from 1. deviates from 1.

Example: D near 0.001, and

F near 0.02, C

/C

varies from 20

to 100

Highly

Highly incompatible incompatible elements

elements

– Greatly concentrated Greatly concentrated in the initial small

in the initial small fraction of melt fraction of melt

produced by partial produced by partial

melting melting

– Subsequently diluted Subsequently diluted as F increases

as F increases

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.

Find a small early partial melt, concentrated

incompatibles there

Incompatibles go to liquid

 As F As F   1, everything is 1, everything is melted, so the

melted, so the

concentration of every trace concentration of every trace element in the liquid => the element in the liquid => the

source rock (C

source rock (C

/C /C

  1) 1)

As F

As F   1 1 C C

/C /C

  1 1 C

C

1

D

(1 F) F

L O

  

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.

D_i the bulk distribution coefficient

As F

As F   0 0 C C

/C /C

  1/D 1/D

If we know the concentration of If we know the concentration of

a trace element in a magma a trace element in a magma C C

, derived by a small degree , derived by a small degree

of batch melting, and we know of batch melting, and we know D D

we can estimate the we can estimate the

concentration of that element concentration of that element

in the

in the source source region (C region (C

). This ). This tells us which area was the

tells us which area was the source.

source.

C C

1

D

(1 F) F

L O

  

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.

Recall then:

D_i the bulk distribution coefficient



For very incompatible elements as D For very incompatible elements as D

  0 0 equation 9-5 equation 9-5 reduces to: reduces to:

eq. 9-7

eq. 9-7 C C

1 F

L O



C C

1

D

(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 produced partial melt produced

D_i the bulk distribution coefficient

Worked Example of Batch Melting:

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

Basalt with the “mode” = Volume% [cm Basalt with the “mode” = Volume% [cm

]: ]:

1. Convert to weight % minerals (W 1. Convert to weight % minerals (W

W W

etc.) etc.) Done, see rightmost column above.

Done, see rightmost column above.

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

15 cm cm

x 3.6g/ cm cm

= 54g 54g/303.9g ~ 0.18

so W W

~ 0.18 ~ 0.18

Worked Example of Batch Worked Example of Batch

Melting:

Melting: Rb and SrRb and Sr

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

A Basalt (ol, cpx, plag) with the mode:

A Basalt (ol, cpx, plag) with the mode:

1. Convert to weight % minerals (W 1. Convert to weight % minerals (W

W W

W W

) )

2. Use equation eq. 9-4: D 2. Use equation eq. 9-4: D

= =   W W

D D

and the table of D (Table 9.1) values for Rb and Sr in each and the table of D (Table 9.1) values for Rb and Sr in each mineral to calculate the bulk distribution coefficients:

mineral to calculate the bulk distribution coefficients:

D D

= 0.045 (Rb incompatible) and D = 0.045 (Rb incompatible) and D

= 0.848 (close to 1) = 0.848 (close to 1)

D

= 0.01 x 0.18 + 0.031 x 0.37 + 0.071 x 0.45 = 0.045

3. 3. Use the batch melting equation Use the batch melting equation

to calculate C

to calculate C

/C /C

for various values of F for various values of F

From Winter (2010) 2

From Winter (2010) 2^ndnd edition An Introduction to Igneous and edition An Introduction to Igneous and Metamorphic Petrology. Prentice Hall.

Metamorphic Petrology. Prentice Hall.

Similarly for F = 0.05 and Sr C_L/C_o = 1.18

Then the ratio

Rb/Sr = 10.78/1.18 = 9.12 Continue with remaining F

For F =0.05 and for Rb: C_L/C_o = 1/ ((0.045(1-0.05)) +0.05) = 10.78

4. 4. Plot C Plot C

/C /C

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.

Rubidium incompatible

strongly partitions i.e. strongly

concentrated in the early small melt

Sr doesn’t change much, so Rb/Sr is approximately the Rb value

Discussion Discussion

 Any ratio of Incompatible to Compatible Any ratio of Incompatible to Compatible elements will be sensitive to the degree of elements will be sensitive to the degree of

partial melting in initial stages partial melting in initial stages

 Our experience with Ternary systems tells us Our experience with Ternary systems tells us it is unrealistic to expect a ratio of the

it is unrealistic to expect a ratio of the minerals in the solid residues to remain minerals in the solid residues to remain

constant.

constant.

 What should we do? What should we do?

Incremental Batch Melting Incremental Batch Melting

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

batches (same equation)

 Must recalculate D Must recalculate D

as solids change and as solids change and minerals are selectively melted

minerals are selectively melted

 Figure 9-2 and 9-3 (earlier slides) show Figure 9-2 and 9-3 (earlier slides) show that the model we just used is most

that the model we just used is most sensitive to D

sensitive to D

at low values of F, so it is at low values of F, so it is most important to use small increments most important to use small increments

in that area. Once F > 0.4, batch melts in that area. Once F > 0.4, batch melts

vary less and are less likely anyway.

vary less and are less likely anyway.

Crystallization Extremes Crystallization Extremes

Either: Crystals remain in equilibrium with Either: Crystals remain in equilibrium with

each melt increment each melt increment

OR The other extreme: separation of each OR 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

 Rayleigh fractional crystallization Rayleigh fractional crystallization

The second extreme: separation of The second extreme: separation of each crystal as it formed = perfectly each crystal as it formed = perfectly

continuous fractional crystallization in a continuous fractional crystallization in a

magma chamber magma chamber

Crystals accumulate on floor of magma Crystals accumulate on floor of magma

chamber, isolating formed crystals chamber, isolating formed crystals

– Concentration of some element in the Concentration of some element in the residual

residual liquid, C _{liquid, C}

is modeled by the is modeled by the Rayleigh equation:

Rayleigh equation:

eq. 9-8

eq. 9-8 C C

/C /C

= F = F

C C

conc. of element in original melt conc. of element in original melt

F fraction of melt remaining after xtals removed

F fraction of melt remaining after xtals removed

Other models are used to analyze Other models are used to analyze



Mixing of magmas Mixing of magmas



Wall-rock assimilation Wall-rock assimilation



Zone refining Zone refining



Combinations of processes Combinations of processes

End of Part 1

The Rare Earth Elements (REE)

Begins Part 2

REEs REEs

 Group IIIA, +3 oxidation state, ionic radius Group IIIA, +3 oxidation state, ionic radius

decreases with increasing atomic number (the decreases with increasing atomic number (the

“Lanthanide contraction”) so right side smaller

“Lanthanide contraction”) so right side smaller ions, fit more readily, more compatible.

ions, fit more readily, more compatible.

bigger smaller

Density Groups of REEs Density Groups of REEs



LREE = light rare earth elements (Sc, La, Ce, Pr, Nd, LREE = light rare earth elements (Sc, La, Ce, Pr, Nd, Pm, Sm, Eu, and Gd; also known as the cerium group) Pm, Sm, Eu, and Gd; also known as the cerium group)



HREE = heavy rare earth elements (Y, Tb, Dy, Ho, Er, HREE = heavy rare earth elements (Y, Tb, Dy, Ho, Er, Tm, Yb, and Lu; also known as the yttrium group)

Tm, Yb, and Lu; also known as the yttrium group)



The densities of the LREEs (as pure elements) range The densities of the LREEs (as pure elements) range from 2.989 (scandium) to 7.9 g/cc (gadolinium), while from 2.989 (scandium) to 7.9 g/cc (gadolinium), while

those of the HREEs are from 8.2 to 9.8, except for those of the HREEs are from 8.2 to 9.8, except for

yttrium (4.47) and ytterbium (between 6.9 and 7) The yttrium (4.47) and ytterbium (between 6.9 and 7) The

latter are groups with the HREE due to similar geological latter are groups with the HREE due to similar geological

behavior.

behavior.

Oxygen Fugacity Oxygen Fugacity

 Fugacity is the partial pressure of a gas phase which takes into account that the gas is able Fugacity is the partial pressure of a gas phase which takes into account that the gas is able to chemically react with other components in the system. A measure of departure from to chemically react with other components in the system. A measure of departure from

Ideal Gas behavior.

Ideal Gas behavior.

 Oxygen fugacity is the measure of the availability of oxygen (within a given system) to Oxygen fugacity is the measure of the availability of oxygen (within a given system) to partake in chemical reactions. It represents the chemical potential of oxygen. It is also a partake in chemical reactions. It represents the chemical potential of oxygen. It is also a

way to quantify the redox state of a given system.

way to quantify the redox state of a given system.

This is very important in terms of determining the stable mineral present in a given This is very important in terms of determining the stable mineral present in a given

geological system.

geological system.

More oxidizing conditions, in igneous or hydrothermal systems for example, favor the More oxidizing conditions, in igneous or hydrothermal systems for example, favor the

crystallization (and stability) of the more oxidized mineral phases.

crystallization (and stability) of the more oxidized mineral phases.

More available oxygen in the system = more oxidizing More available oxygen in the system = more oxidizing

 System precipitates components with more oxygen (i.e. System precipitates components with more oxygen (i.e.

Hematite FeHematite Fe₂₂OO₃₃ (ratio 3/2 = 1.5) would crystallize, rather than Magnetite Fe (ratio 3/2 = 1.5) would crystallize, rather than Magnetite Fe₃₃OO₄₄ (ratio 4/3 (ratio 4/3

= 1.333).

= 1.333).

Incompatible elements Incompatible elements

 An element unsuitable in size and/or charge to the cation sites of the rock forming minerals. The An element unsuitable in size and/or charge to the cation sites of the rock forming minerals. The partition coefficient for them between rock-forming minerals and melt is much smaller than 1.

partition coefficient for them between rock-forming minerals and melt is much smaller than 1.

 During the partial melting of the Earth's mantle and crust, elements that have difficulty in During the partial melting of the Earth's mantle and crust, elements that have difficulty in

entering cation sites of the basaltic minerals (Olivine, Clinopyroxenes, Ca-rich Plagioclases) are entering cation sites of the basaltic minerals (Olivine, Clinopyroxenes, Ca-rich Plagioclases) are concentrated in the liquid phase of the magma. They are destined for later minerals and glasses.

concentrated in the liquid phase of the magma. They are destined for later minerals and glasses.

For example, Potassium K enters the K-spars: Sanidine, Orthoclase, Microcline very late in For example, Potassium K enters the K-spars: Sanidine, Orthoclase, Microcline very late in fractionation.

fractionation.

 Two groups of incompatible elements are known by acronyms. One group includes elements Two groups of incompatible elements are known by acronyms. One group includes elements having large ionic radius, (called LILE, or large-ion lithophile elements. This LILE group includes having large ionic radius, (called LILE, or large-ion lithophile elements. This LILE group includes potassium, rubidium, cesium, strontium, and barium.

potassium, rubidium, cesium, strontium, and barium.

 The other group includes elements of large ionic valences (or high charges), such as zirconium The other group includes elements of large ionic valences (or high charges), such as zirconium

ZrZr⁺⁴⁺⁴ , niobium, hafnium, rare earth elements (REE), thorium, uranium and tantalum (called , niobium, hafnium, rare earth elements (REE), thorium, uranium and tantalum (called HFSE, or high field strength elements). These can occur in pegmatites, for example the alkaline HFSE, or high field strength elements). These can occur in pegmatites, for example the alkaline pegmatites we will see at Cranberry Lake.

pegmatites we will see at Cranberry Lake.

Europium Europium



Note: at low Oxygen fugacity, Europium can have a +2 Note: at low Oxygen fugacity, Europium can have a +2 valence, and Eu

valence, and Eu

can be more abundant than Eu can be more abundant than Eu

Eu

is a Large Ion Lithophile (LIL)

Eu

is a high field strength (HFS) element.

LILs include K, Rb, Cs, Ba, Pb

, Sr and Eu

LIL’s are low field strength, e.g. Potassium’s ion is K

, and are

generally more mobile if a fluid is adjacent.



The term LILE is The term LILE is restricted to

restricted to lithophile trace lithophile trace

elements having a elements having a

large

large ionic radius ionic radius to charge ratio;

to charge ratio;

that have ionic that have ionic

radii greater than radii greater than

those of Ca

those of Ca

and and Na Na

, some of the , some of the

largest cations largest cations

common to rock common to rock

forming minerals.

forming minerals.

By this definition, By this definition,

LILEs are K, Rb, LILEs are K, Rb,

Cs, Sr, Ba, Pb and

Cs, Sr, Ba, Pb and

Eu Eu

-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) H

He

Li Be

B C

N O

F

Sc Fe

Ni Ne MgSi

S ArCa Ti

Pt Pb Sn Ba

V K NaAlP

Cl

Th U

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

more functional by normalizing to a standard

 estimates of primordial mantle REE estimates of primordial mantle REE

 chondrite meteorite concentrations chondrite meteorite concentrations

Oddo-Harkins Rule: atoms with even atomic numbers are more stable, and thus more abundant, than their odd-numbered neighbors:

elements with odd atomic numbers have one unpaired proton and are more likely to capture another

 Europium anomaly Europium anomaly

 A negative dip is evidence liquid was in A negative dip is evidence liquid was in

equilibrium with now-absent plagioclase*, equilibrium with now-absent plagioclase*,

which captured Eu which captured Eu

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.

* It floated away

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 fractionation, assimilation, etc. in a document fractionation, assimilation, etc. in a

suite of rocks suite of rocks



TE more sensitive TE more sensitive   larger variations as larger variations as process continues

process continues

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 processes fractional crystallization processes

Example: can use REE to distinguish between high Example: can use REE to distinguish between high

pressure and low pressure sources of a mantle- pressure and low pressure sources of a mantle-

derived magma derived magma

In the deep continental crust, and at depths over In the deep continental crust, and at depths over

about 100 km in the mantle, garnet and about 100 km in the mantle, garnet and

clinopyroxene are important phases, which remain clinopyroxene are important phases, which remain

as residual solids during the generation of up to as residual solids during the generation of up to

15-20% partial melting 15-20% partial melting

Application of Trace Elements to

Igneous Systems

Garnet

Garnet 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 concentration of Tb, Er, phase in the source left behind) expect a concentration of Tb, Er, Yb, and Lu in the Garnet

Yb, and Lu in the Garnet Shallow (< 40

Shallow (< 40 km) partial km) partial melting of the melting of the mantle will have mantle will have plagioclase in plagioclase in the residuum the residuum and a Eu

and a Eu

anomaly will anomaly will result

result

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. Eu²⁺ 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.

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

Igneous and Metamorphic Petrology. Prentice Hall.

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 in Thorpe (ed.), Andesites: Orogenic andesites and related rocks. Wiley. Chichester. pp. 525-548

Thorpe (ed.), Andesites: 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.

Petrology Field Trip to Bemco Mining District, a side trip

Ores from weathered Sulfide deposits

• Mineral deposits containing sulfide

minerals, e.g. copper sulfides that are

subjected to weathering, can go into solution and trickle down to the

reducing conditions

below the water table, where native metals or rich concentrations of ores are precipitated.

Black Smokers, hydrothermal circulations

Gossan Intensely oxidized, weathered or decomposed rock, usually the upper and exposed part of an ore deposit or mineral vein. In the classic gossan or iron cap all that remains is iron oxides and quartz often in the form of boxworks, quartz lined cavities retaining the shape of the dissolved ore minerals

.

Solubility in water

The Solubility Rules

1. Salts containing Group I elements are soluble (Li⁺, Na⁺, K⁺, Cs⁺, Rb⁺). Exceptions to this rule are rare. Salts containing the ammonium ion (NH4+) are also soluble.

2. Salts containing nitrate ion (NO3-) are generally soluble.

3. Salts containing Cl ^-, Br ^-, I ^- are generally soluble. Important exceptions to this rule are halide salts of Ag⁺, Pb²⁺, and (Hg2)²⁺. Thus, AgCl, PbBr2, and Hg2Cl2 are all insoluble.

4. Most silver salts are insoluble. AgNO3 and Ag(C2H3O2) are common soluble salts of silver; virtually anything else is insoluble.

5. Most sulfate salts are soluble, for example FeSO

is soluble.

6. Most hydroxide salts are only slightly soluble. Hydroxide salts of Group I elements are soluble. Hydroxide salts of Group II elements (Ca, Sr, and Ba) are slightly soluble. Hydroxide salts of transition metals and Al³⁺ are insoluble. Thus, Fe(OH)3, Al(OH)3, Co(OH)2 are not soluble.

7. Most sulfides of transition metals are highly insoluble. Thus, CuS, FeS, FeS

, ZnS, Ag

S are all insoluble. Arsenic, antimony, bismuth, and lead sulfides are also insoluble.

8. Carbonates are frequently insoluble. Group II carbonates (Ca, Sr, and Ba) are insoluble. Some other insoluble carbonates include FeCO3 and PbCO3. 9. Chromates are frequently insoluble. Examples: PbCrO4, BaCrO4

10. Phosphates are frequently insoluble. Examples: Ca3(PO4)2, Ag3PO4

11. Fluorides are frequently insoluble. Examples: BaF2, MgF2 PbF2.

Putting insoluble sulfides into solution

• Oxidizing Zone above the water table

• Sulfide minerals, for example ferrous and copper sulfides, are subject to

weathering.

• Sulfide minerals are oxidized near the surface and produce sulfuric acid. For example:

• FeS

(s) + 7O + H

O →FeSO

(aq) + H

SO

Reaction and Trickling Down

• Iron sulfate reacts with sulfides, they go into solution as sulfates, acid rainwater then carries, for example copper, as copper sulfate, down to the water table.

• CuS(s) + Fe

(SO

)

(aq) →2FeSO

(aq) + S(s) + CuSO

(aq)

• The net result is that dissolved copper sulfide

trickles down from the oxidizing upper portion of

the deposit to that portion at and just below the

water table.

Reducing Zone below the water table

• Below the water table, where additional sulfide minerals remain solid and unoxidized (e.g. Pyrite FeS

), any iron sulfide grains present will react

with the copper sulfate solution, putting iron into solution and precipitating copper.

• FeS

(s) + CuSO

(aq) → FeSO

(aq) + Cu(s) + 2S(s)

Hydrothermal Deposit, Bemco Mine

Hydrothermal Deposit, Bemco Mine