rock suites, trace elements and radiogenic isotopes geos 408/508 lectures 4-6

Rock suites, trace elements and Rock suites, trace elements and radiogenic isotopesradiogenic isotopes

GEOS 408/508GEOS 408/508

Lectures 4-6Lectures 4-6

MgO and FeOMgO and FeO

AlAl22OO33 and CaO and CaO

SiO2SiO2

NaNa22O, KO, K22O, TiOO, TiO22, ,

PP22OO55

Rock suitesRock suites

The totality of major compositions found in a spatio-temporal domain The totality of major compositions found in a spatio-temporal domain of interest;of interest;

Typically display a range of major, trace and isotopic compositions;Typically display a range of major, trace and isotopic compositions; Examples: calc-alkaline (banatite) suites in arc regions; bimodal Examples: calc-alkaline (banatite) suites in arc regions; bimodal

(basalt-rhyolite) suites in continental extension, etc;(basalt-rhyolite) suites in continental extension, etc; Perhaps the most important lesson to take home regarding rocks suites Perhaps the most important lesson to take home regarding rocks suites

is that no single magmatic rock composition can be indicative of a past is that no single magmatic rock composition can be indicative of a past tectonic setting - use instead the range of rock compositions.tectonic setting - use instead the range of rock compositions.

More Trace ElementsMore Trace Elements

Note magnitue Note magnitue of major of major element element changeschanges

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.

Generating diversityGenerating diversity

Fractionation = selective crystallization and removal of crystals from an Fractionation = selective crystallization and removal of crystals from an evolving magma;evolving magma;

Mixing= co-aggregation of two (or more) different magmas;Mixing= co-aggregation of two (or more) different magmas; Unmixxing (not common) = Generation of two liquids out of one via melt Unmixxing (not common) = Generation of two liquids out of one via melt

immiscibility;immiscibility; Assimilation and fractional crystallization (AFC)= wall rock incorporation Assimilation and fractional crystallization (AFC)= wall rock incorporation

coupled with internal fractionation;coupled with internal fractionation; Source heterogeneity;Source heterogeneity; ““secondary”, postmagmatic processes = hydrothermal alteration, weathering, secondary”, postmagmatic processes = hydrothermal alteration, weathering,

etc.etc.

Bivariate Bivariate (x-y) (x-y)

diagramsdiagrams

HarkerHarkerdiagram diagram

forforCraterCraterLakeLake

Figure 2. Harker variation diagram for 310 analyzed volcanic rocks from Crater Lake (Mt. Mazama), Oregon Cascades. Data compiled by Rick Conrey (personal communication).

Models of Magmatic EvolutionModels of Magmatic Evolution

hypothetical set of related volcanics.

Oxide B BA A D RD R

SiO2 50.2 54.3 60.1 64.9 66.2 71.5

TiO2 1.1 0.8 0.7 0.6 0.5 0.3

Al2O3 14.9 15.7 16.1 16.4 15.3 14.1

Fe2O3* 10.4 9.2 6.9 5.1 5.1 2.8

MgO 7.4 3.7 2.8 1.7 0.9 0.5

CaO 10.0 8.2 5.9 3.6 3.5 1.1

Na2O 2.6 3.2 3.8 3.6 3.9 3.4

K2O 1.0 2.1 2.5 2.5 3.1 4.1

LOI 1.9 2.0 1.8 1.6 1.2 1.4

Total 99.5 99.2 100.6 100.0 99.7 99.2

B = basalt, BA = basaltic andesite, A = andesite, D = dacite,

RD = rhyo-dacite, R = rhyolite. Data from Ragland (1989)

Table 5 . Chemical analyses (wt. %) of a

Harker diagramHarker diagram Smooth trendsSmooth trends Model with 3 assumptions:Model with 3 assumptions:

1 Rocks are related by FX1 Rocks are related by FX

2 Trends = liquid line of 2 Trends = liquid line of descentdescent

3 The basalt is the parent 3 The basalt is the parent magma from which the others magma from which the others are derivedare derived

Figure 7. Stacked variation diagrams of hypothetical components X and Y (either weight or mol %). P = parent, D = daughter, S = solid extract, A, B, C = possible extracted solid phases. For explanation, see text. From Ragland (1989). Basic Analytical Petrology, Oxford Univ. Press.

Extrapolate BA Extrapolate BA B and B and further to low SiOfurther to low SiO22

KK22O is first element to O is first element to 0 0 (at SiO(at SiO22 = 46.5) = 46.5)

46.5% SiO2 is interpreted to be the concentration in the bulk solid extract and the blue line the concentration of all other oxides

Figure 7. Stacked Harker diagrams for the calc-alkaline volcanic series of Table 8-5 (dark circles). From Ragland (1989). Basic Analytical Petrology, Oxford Univ. Press.

Extrapolate the other curves Extrapolate the other curves back BA back BA B B blue line and blue line and read off X of mineral extractread off X of mineral extract

Oxide Wt% Cation Norm

SiO2 46.5 ab 18.3TiO2 1.4 an 30.1Al2O3 14.2 di 23.2Fe2O3* 11.5 hy 4.7MgO 10.8 ol 19.3CaO 11.5 mt 1.7Na2O 2.1 il 2.7K2O 0Total 98.1 100

Results:Results: Remove plagioclase, olivine, Remove plagioclase, olivine, pyroxene and Fe-Ti oxidepyroxene and Fe-Ti oxide

Then repeat for each increment BA Then repeat for each increment BA A etc. A etc.

Now note Now note magnitude of magnitude of trace element trace element changeschanges

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

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

Goldschmidt’s rulesGoldschmidt’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 liquidsolid over the liquid

3. If 2 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)

eq. 2eq. 2 K = =K = =

K =K = equilibrium constantequilibrium constant

a a solidsolid

a a liquidliquidii

ii

XX solidsolid

XX liquidliquid

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 systemconcentration in the system

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

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

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

eq. 4:eq. 4: DDii = = W WAA D Dii

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

Homework 3Homework 3

Calculate partition coefficient of Sr for one Calculate partition coefficient of Sr for one (any) one of the rocks in Cecil’s data, (any) one of the rocks in Cecil’s data, assuming that the actual minerals are the assuming that the actual minerals are the norms you calculated for that rock. Get the norms you calculated for that rock. Get the Kd’s from GERM’s tabulated source online Kd’s from GERM’s tabulated source online and use mineral-silicic melt coefficient.and use mineral-silicic melt coefficient.

Trace elements strongly partitioned into a single Trace elements strongly partitioned into a single mineralmineral

Ni - olivine = 14Ni - olivine = 14

Figure 1a.Figure 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 1b.Figure 1b. Zr Harker Diagram for Crater Lake. From data compiled by Rick Conrey. From Zr 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.

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

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

eq. 5eq. 5

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 eq. 5 using eq. 5

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)

Figure 2.Figure 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.

Highly Highly incompatibleincompatible elements elements Greatly concentrated in Greatly concentrated in

the initial small fraction the initial small fraction of melt produced by of melt produced by partial meltingpartial melting

Subsequently diluted as Subsequently diluted as F increasesF increases


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

1) 1)

As F As F 1 1

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

equation 5 equation 5 reduces reduces to:to:

eq. 7eq. 7

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 -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 equation eq. 4: Use equation eq. 4: 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 Use the batch melting equation

(5)(5) to calculate Cto calculate CLL/C/COO for various values of F for 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 3.Figure 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:

eq. 8eq. 8 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 elem ents in basaltic and andes itic 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 f rom 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 4.Figure 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 5.Figure 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. 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 7.Figure 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 1a.Figure 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 elem ents in basaltic and andes itic 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 f rom 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 3.Figure 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 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 6.Table 6. After Green (1980). Tectonophys., After Green (1980). Tectonophys., 6363, 367-, 367-385. From Winter (2001) An Introduction to Igneous 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 8.Figure 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 in Thorpe (ed.), Andesites: Orogenic andesites and related rocks. Wiley. Chichester. pp. 525-548(ed.), Andesites: Orogenic andesites and related rocks. Wiley. Chichester. pp. 525-548 , Coish et al. (1986), , Coish et al. (1986), Amer. Amer. J. Sci., 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.

Degree of melting, incompatible, compatible elements

Partial melting

Melt

Residue

Melt

Cumulate

Fractional

crystallization

Source region Magma chamber

melts

solids

cl

c0

=

1

D + F ( 1 − D )

REEs, spidergrams, HFSE, “anomalies”

HFSE

IsotopesIsotopes

Same Z, different A (variable # of neutrons)Same Z, different A (variable # of neutrons)

General notation for a nuclide:General notation for a nuclide: 661414CC

IsotopesIsotopes

Same Z, different A (variable # of neutrons)Same Z, different A (variable # of neutrons)

General notation for a nuclide:General notation for a nuclide: 661414CC

As n varies As n varies different isotopes of an element different isotopes of an element

1212C C 1313C C 1414CC

HW 4HW 4 Use the Cecil database to plot the incompatible Use the Cecil database to plot the incompatible

trace element data relative to primitive mantle trace element data relative to primitive mantle values for granitoids; do they exhibit any values for granitoids; do they exhibit any significant anomalies, are there any trends significant anomalies, are there any trends worthwhile interpreting?worthwhile interpreting?

Determine the REE patterns (rel. to PM) and the Determine the REE patterns (rel. to PM) and the magnitude of Eu anomalies;magnitude of Eu anomalies;

Use the Girardi et al 2012 paper as an example to Use the Girardi et al 2012 paper as an example to make interpretations re the origin of magmas from make interpretations re the origin of magmas from the Rotberg area.the Rotberg area.

Stable IsotopesStable Isotopes

Stable: last ~ foreverStable: last ~ forever Chemical fractionationChemical fractionation is is impossible impossible Mass fractionationMass fractionation is the only type possible is the only type possible

Example: Oxygen IsotopesExample: Oxygen Isotopes

Concentrations expressed by reference to a standardConcentrations expressed by reference to a standard

International standard for O isotopes = International standard for O isotopes = standard mean standard mean ocean water (SMOW)ocean water (SMOW)

1616OO 99.756% of natural 99.756% of natural oxygenoxygen1717OO 0.039% 0.039% ““1818OO 0.205% 0.205% ““

1818OO and and 1616OO are the commonly used isotopes are the commonly used isotopes and their ratio is expressed as and their ratio is expressed as ::

1818O/O/1616O) = O) = eqeq11

result expressed in per mille (‰)result expressed in per mille (‰)

(( O/O/ O)O) (( O/O/ O)O)

(( O/O/ O)O)xx10001000

1818 1616samplesample

1818 1616SMOWSMOW

1818 1616SMOWSMOW

What is What is of SMOW?? of SMOW??

What is What is for meteoric water? for meteoric water?


Evaporation seawater Evaporation seawater water vapor (clouds) water vapor (clouds) Light isotope enriched in vapor > liquidLight isotope enriched in vapor > liquid Pretty efficient, since Pretty efficient, since mass = 1/8 total mass mass = 1/8 total mass


Evaporation seawater Evaporation seawater water vapor (clouds) water vapor (clouds) Light isotope enriched in vapor > liquidLight isotope enriched in vapor > liquid Pretty efficient, since Pretty efficient, since mass = 1/8 total mass mass = 1/8 total mass

==

therefore therefore < <

thusthus cloudsclouds is (-) is (-)

(( O/O/ O)O) (( O/O/ O)O)

(( O/O/ O)O)xx 10001000

1818 1616vaporvapor

1818 1616SMOWSMOW

1818 1616SMOWSMOW

(( O/O/ O)O)1818 1616VaporVapor (( O/O/ O)O)1818 1616

SMOWSMOW

Figure 9-9. Relationship between d(18O/16O) and mean annual temperature for meteoric precipitation, after Dansgaard (1964). Tellus, 16, 436-468.

Oxygen isotopes Can determine crustal recycling

Mantle-derived rocks = delta18O ~ 5-6.5 permilMantle-derived rocks = delta18O ~ 5-6.5 permil

Crustal Rocks that have interacted with waters: Crustal Rocks that have interacted with waters: Anything between -2 to +24 permilAnything between -2 to +24 permil

Oxygen has the mass advantage over other isotopesOxygen has the mass advantage over other isotopes

O and H isotopes - juvenile vs. meteoric vs. O and H isotopes - juvenile vs. meteoric vs. brine waterbrine water

1818O for mantle rocks O for mantle rocks surface-reworked surface-reworked sediments: evaluate contamination of mantle-sediments: evaluate contamination of mantle-derived magmas by crustal sedimentsderived magmas by crustal sediments

Stable isotopes useful in assessing relative Stable isotopes useful in assessing relative contribution of various reservoirs, each with contribution of various reservoirs, each with a distinctive isotopic signaturea distinctive isotopic signature

Radioactive IsotopesRadioactive Isotopes

Unstable isotopes decay to other nuclidesUnstable isotopes decay to other nuclides The rate of decay is constant, and not The rate of decay is constant, and not

affected by P, T, X…affected by P, T, X… ParentParent nuclide = nuclide = radioactiveradioactive nuclide that nuclide that

decaysdecays DaughterDaughter nuclide(s) are the nuclide(s) are the radiogenicradiogenic

atomicatomic products products

Isotopic variations between rocks, etc. due to:Isotopic variations between rocks, etc. due to:1. Mass fractionation1. Mass fractionation (as for stable isotopes) (as for stable isotopes)

Only effective for light isotopes: H He C O SOnly effective for light isotopes: H He C O S

Isotopic variations between rocks, etc. due to:Isotopic variations between rocks, etc. due to:1. Mass fractionation (as for stable isotopes)1. Mass fractionation (as for stable isotopes)

2. Daughters produced in varying proportions 2. Daughters produced in varying proportions resulting from previous event of resulting from previous event of chemicalchemical fractionationfractionation

40K 40Ar by radioactive decay

Basalt rhyolite by FX (a chemical fractionation process)

Rhyolite has more K than basalt

40K more 40Ar over time in rhyolite than in basalt

40Ar/39Ar ratio will be different in each

Isotopic variations between rocks, etc. due to:Isotopic variations between rocks, etc. due to:1. Mass fractionation (as for stable isotopes)1. Mass fractionation (as for stable isotopes)

2. Daughters produced in varying proportions 2. Daughters produced in varying proportions resulting from previous event of chemical resulting from previous event of chemical fractionationfractionation

3. Time3. TimeThe longer The longer 4040K K 4040Ar decay takes place, the greaterAr decay takes place, the greater

the difference between the basalt and rhyolite will bethe difference between the basalt and rhyolite will be

Radioactive DecayRadioactive Decay

The Law of Radioactive Decay

eq. 11 dN

dtN or

dN

dt= N

# pa

rent

ato

ms

# pa

rent

ato

ms

time time

11

½½

¼¼

D = NeD = Nett - N - N = N(e= N(ett -1) eq 14 -1) eq 14

age of a sample (t) age of a sample (t) if we know:if we know: DD the amount of the daughter nuclide produced the amount of the daughter nuclide produced

NN the amount of the original parent nuclide remaining the amount of the original parent nuclide remaining

the decay constant for the system in questionthe decay constant for the system in question

The appropriate decay equation is:The appropriate decay equation is:

eq 16eq 16 4040Ar = Ar = 4040ArAroo + + 4040K(eK(e--t t -1)-1)

Where Where ee = 0.581 x 10 = 0.581 x 10-10-10 a a-1-1 (proton capture) (proton capture)

and and = 5.543 x 10 = 5.543 x 10-10-10 a a-1 -1 (whole process) (whole process)

e

Sr-Rb System Sr-Rb System

8787Rb Rb 8787SrSr + a beta particle ( + a beta particle ( = 1.42 x 10 = 1.42 x 10-11-11 a a-1-1))

Rb behaves like K Rb behaves like K micas and alkali feldspar micas and alkali feldspar

Sr behaves like Ca Sr behaves like Ca plagioclase and apatite (but not plagioclase and apatite (but not clinopyroxene)clinopyroxene)

8888Sr : Sr : 8787Sr : Sr : 8686Sr : Sr : 8484Sr ave. sample = 10 : 0.7 : 1 : 0.07Sr ave. sample = 10 : 0.7 : 1 : 0.07

8686SrSr is a stable isotope, and not created by breakdown is a stable isotope, and not created by breakdown of any other parentof any other parent

Isochron TechniqueIsochron Technique

Requires 3 or more cogenetic samples with a range of Requires 3 or more cogenetic samples with a range of Rb/SrRb/Sr

Could be:Could be:

• 3 cogenetic rocks derived 3 cogenetic rocks derived from a single source by from a single source by partial melting, FX, etc.partial melting, FX, etc.

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

Isochron TechniqueIsochron Technique

Requires 3 or more cogenetic samples with a range Requires 3 or more cogenetic samples with a range of Rb/Srof Rb/Sr

Could be:Could be:

• 3 cogenetic rocks derived 3 cogenetic rocks derived from a single source by from a single source by partial melting, FX, etc.partial melting, FX, etc.

• 3 coexisting minerals with 3 coexisting minerals with different K/Ca ratios in a different K/Ca ratios in a single rocksingle rock

For values of For values of t less than 0.1: et less than 0.1: ett-1 -1 tt

Thus eq. 9-15 for t < 70 Ga (!!) reduces to:Thus eq. 9-15 for t < 70 Ga (!!) reduces to:

eq 9-18 eq 9-18 8787Sr/Sr/8686Sr = (Sr = (8787Sr/Sr/8686Sr)Sr)oo + ( + (8787Rb/Rb/8686Sr)Sr)tt

y = b + x y = b + x m m

= equation for a line in = equation for a line in 8787Sr/Sr/8686Sr vs. Sr vs. 8787Rb/Rb/8686Sr plotSr plot

Recast age equation by dividing through by stable Recast age equation by dividing through by stable 8686SrSr

8787Sr/Sr/8686Sr = (Sr = (8787Sr/Sr/8686Sr)Sr)oo + ( + (8787Rb/Rb/8686Sr)(eSr)(ett -1) eq 9-17 -1) eq 9-17

= 1.4 x 10= 1.4 x 10-11-11 a a-1-1

a b c to86Sr

87Sr

o( )

86Sr

87Sr

86Sr

87Rb

Begin with 3 rocks plotting at Begin with 3 rocks plotting at a b ca b c at time at time ttoo

After some time increment (tAfter some time increment (t00 tt11) each sample loses ) each sample loses

some some 8787Rb and gains an equivalent amount of Rb and gains an equivalent amount of 8787SrSr

a b c

a1b1

c1t1

to

86Sr

87Sr

86Sr

87Rb

86Sr

87Sr

o( )

At timeAt time t t22 each rock system has evolved each rock system has evolved new line new line

Again still linear and steeper lineAgain still linear and steeper line

a b c

a1b1

c1a2

b2

c2t1

to

t2

86Sr

87Sr

86Sr

87Sr

o( )

86Sr

87Rb

Isochron technique produces 2 valuable things:Isochron technique produces 2 valuable things:

1. The age of the rocks (from the slope = 1. The age of the rocks (from the slope = t)t)

2. 2. ((8787Sr/Sr/8686Sr)Sr)oo = the initial value of = the initial value of 8787Sr/Sr/8686SrSr

Figure 9-9. Rb-Sr isochron for the Eagle Peak Pluton, central Sierra Nevada Batholith, California, USA. Filled circles are whole-rock analyses, open circles are hornblende separates. The regression equation for the data is also given. After Hill et al. (1988). Amer. J. Sci., 288-A, 213-241.

Figure 9-13.Figure 9-13. Estimated Rb and Sr isotopic evolution of the Earth’s upper mantle, assuming a large-scale melting Estimated Rb and Sr isotopic evolution of the Earth’s upper mantle, assuming a large-scale melting event producing granitic-type continental rocks at 3.0 Ga b.p After Wilson (1989). Igneous Petrogenesis. Unwin event producing granitic-type continental rocks at 3.0 Ga b.p After Wilson (1989). Igneous Petrogenesis. Unwin Hyman/Kluwer.Hyman/Kluwer.

The Sm-Nd System The Sm-Nd System

Both Sm and Nd are LREEBoth Sm and Nd are LREE Incompatible elements fractionate Incompatible elements fractionate melts melts Nd has lower Z Nd has lower Z larger larger liquids > does Sm liquids > does Sm

147147Sm Sm 143143Nd by alpha decayNd by alpha decay = 6.54 x 10= 6.54 x 10-13-13 a a-1 -1 (half life 106 Ga)(half life 106 Ga)

Decay equation derived by reference to Decay equation derived by reference to the the non-radiogenicnon-radiogenic 144144Nd Nd 143143Nd/Nd/144144Nd = (Nd = (143143Nd/Nd/144144Nd)Nd)oo

+ (+ (147147Sm/Sm/144144Nd)Nd)tt

Evolution curve is opposite to Rb - SrEvolution curve is opposite to Rb - Sr

Figure 9-15.Figure 9-15. Estimated Nd isotopic evolution of the Earth’s upper mantle, assuming a large-scale melting Estimated Nd isotopic evolution of the Earth’s upper mantle, assuming a large-scale melting or enrichment event at 3.0 Ga b.p. After Wilson (1989). Igneous Petrogenesis. Unwin Hyman/Kluwer.or enrichment event at 3.0 Ga b.p. After Wilson (1989). Igneous Petrogenesis. Unwin Hyman/Kluwer.

Systematic geographic distribution of isotopic ratios

The 0.706 line through the Sierra Nevada and north

Fractionation, assimilation, mixing

15.70

15.80

15.90

16.00

16.10

16.20

16.30

16.40

16.50

16.60

0 5 10 15 20 25 30

eruption sequence time to right

Al2O3 (wt%)

44.50

45.00

45.50

46.00

46.50

47.00

47.50

48.00

0 5 10 15 20 25 30

eruption sequence time to right

SiO

2 (wt%)

Simple Mixing ModelsSimple Mixing ModelsBinaryBinary

All analyses fall between All analyses fall between two reservoirs as magmas two reservoirs as magmas

mixmix

TernaryTernaryAll analyses fall within All analyses fall within

triangle determined triangle determined by three reservoirsby three reservoirs

Figure 14-5. Winter (2001) An Introduction to Igneous and Metamorphic Petrology. Prentice Hall.

HW5HW5

Determine the initial Sr and Nd isotopes for the Cecil Determine the initial Sr and Nd isotopes for the Cecil database;database;

Plot the initial Sr vs. Nd isotopes, 87Sr/86Sr vs. 1/Sr and Plot the initial Sr vs. Nd isotopes, 87Sr/86Sr vs. 1/Sr and 143Nd/144Nd vs. 1/Nd; is there one or are there more 143Nd/144Nd vs. 1/Nd; is there one or are there more sources of magmas? How many? sources of magmas? How many?

Do the isotopes and isotope-elemental plots indicate any Do the isotopes and isotope-elemental plots indicate any mixing curves? How many components? Plot at least one mixing curves? How many components? Plot at least one mixing line using IgPet (or similar).mixing line using IgPet (or similar).

Other radiogenic systems and Other radiogenic systems and utilitiesutilities

Pb-Pb (u and Th decay)- good for identifying Pb-Pb (u and Th decay)- good for identifying sedimentary sources in magma (high U/Pb)sedimentary sources in magma (high U/Pb)

He isotopes - can detect pristine, undegassed He isotopes - can detect pristine, undegassed mantle in some plumesmantle in some plumes

Ca isotopes - can trace old crustal componentsCa isotopes - can trace old crustal components Hf isotopes - useless except perhaps when used in Hf isotopes - useless except perhaps when used in

situ with U-Pb dating of zirconssitu with U-Pb dating of zircons Re-Os - can effectively fingerprint crustal sources Re-Os - can effectively fingerprint crustal sources

and date mantle events. and date mantle events.

The U-Pb-Th SystemThe U-Pb-Th SystemVery complex system. Very complex system.

3 radio3 radioactiveactive isotopes of U: isotopes of U: 234234U, U, 235235U, U, 238238UU 3 radio3 radiogenicgenic isotopes of Pb: isotopes of Pb: 206206Pb, Pb, 207207Pb, and Pb, and 208208PbPb

Only Only 204204Pb is strictly non-radiogenicPb is strictly non-radiogenic U, Th, and Pb are U, Th, and Pb are incompatibleincompatible elements, & elements, &

concentrate in early meltsconcentrate in early melts Isotopic composition of Pb in rocks = function ofIsotopic composition of Pb in rocks = function of

238238U U 234234U U 206206PbPb (( = 1.5512 x 10 = 1.5512 x 10-10-10 a a-1-1)) 235235U U 207207PbPb (( = 9.8485 x 10 = 9.8485 x 10-10-10 a a-1-1)) 232232Th Th 208208PbPb (( = 4.9475 x 10 = 4.9475 x 10-11-11 a a-1-1))

Common PbCommon Pb

He isotopes

rock suites, trace elements and radiogenic isotopes geos 408/508 lectures 4-6

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