Post on 20-Jan-2016
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).
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
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
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
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
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
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
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
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.
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
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.
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
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.
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
La Ce Nd Sm Eu Tb Er Yb Lu
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
La Ce Nd Sm Eu Tb Er Yb Lu
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?
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
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
==
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