Trace ElementsTrace ElementsNoteNotemagnitudemagnitudeof of majormajorelementelementchangeschangesFigure 8-2. Harker variation diagram for310 analyzed volcanic rocks from CraterLake (Mt. Mazama), Oregon Cascades.Data compiled by Rick Conrey (personalcommunication). From Winter (2001) AnFrom Winter (2001) AnIntroduction to Igneous and MetamorphicIntroduction to Igneous and MetamorphicPetrology. Prentice Hall.Petrology. Prentice Hall.wt %wt %Figure 9-1.Figure 9-1. Harker Diagram for Crater Lake. From data Harker Diagram for Crater Lake. From datacompiled by Rick compiled by Rick ConreyConrey. From Winter (2001) An Introduction. From Winter (2001) An Introductionto Igneous and Metamorphic Petrology. Prentice Hall.to Igneous and Metamorphic Petrology. Prentice Hall.NoteNotemagnitudemagnitudeof of tracetraceelementelementchangeschangesTrace ElementsTrace ElementsppmppmppmppmElement DistributionElement DistributionGoldschmidtGoldschmidt’’s rules (simplistic, but useful)s rules (simplistic, but useful)1.1. Two ions with the same valence and radiusTwo ions with the same valence and radiusshould exchange easily and enter a solidshould exchange easily and enter a solidsolution in amounts equal to their overallsolution in amounts equal to their overallproportionsproportionsHow does Rb behave? Ni?How does Rb behave? Ni?GoldschmidtGoldschmidt’’s ruless rules2. If two ions have a similar radius and the same2. If two ions have a similar radius and the samevalence: the smaller ion is preferentially incorporatedvalence: the smaller ion is preferentially incorporatedinto the solid over the liquidinto the solid over the liquidFig. 6-10. Isobaric T-X phasediagram at atmosphericpressure After Bowen andShairer (1932), Amer. J. Sci. 5thSer., 24, 177-213. From WinterFrom Winter(2001) An Introduction to(2001) An Introduction toIgneous and MetamorphicIgneous and MetamorphicPetrology. Prentice Hall.Petrology. Prentice Hall.Relative ionic radii for common valencesand coordination numbersPreference forPreference formineral phasemineral phasePreferencePreferencefor meltfor meltPlot of ionic radius vs. ionic charge fortrace elements of geological interest.Ionic radii are quoted for eight-foldcoordination to allow for comparisonbetween elements. From Rollinson(1993).Ionic chargeIonic chargevs. radiusvs. radius3. If two ions have a similar radius, but differentvalence: the ion with the higher charge ispreferentially incorporated into the solid over theliquidChemical FractionationChemical FractionationThe uneven distribution of an ion betweenThe uneven distribution of an ion betweentwo competing (equilibrium) phasestwo competing (equilibrium) phasesExchange equilibrium of a Exchange equilibrium of a componentcomponent ii betweenbetweentwo two phasesphases (solid and liquid) (solid and liquid)ii (liquid)(liquid) = = ii (solid)(solid)KKDD = = = = K =K = equilibrium constantequilibrium constanta a solidsolida a liquidliquidiiiiγγ XX solidsolidγγ XX liquidliquidiiiiiiiiTrace element concentrations are in theTrace element concentrations are in theHenryHenry’’s Law region of concentration, sos Law region of concentration, sotheir activity varies in direct relation to theirtheir activity varies in direct relation to theirconcentration in the system, where [a] = (c)concentration in the system, where [a] = (c)Thus if Thus if XXNiNi in the system doubles the in the system doubles the XXNiNi ininall all phases will doublephases will doubleThis does not mean that This does not mean that XXNiNi in all phasesin all phasesis the same, since trace elements dois the same, since trace elements dofractionate. Rather the fractionate. Rather the XXNiNi within eachwithin eachphase will vary in proportion to thephase will vary in proportion to thesystem concentrationsystem concentrationincompatibleincompatible elements are concentrated in the elements are concentrated in themeltmelt(K(KDD or D) or D) «« 1 1compatiblecompatible elements are concentrated in the elements are concentrated in thesolidsolidKKDD or D or D »» 1 1where D is the partition coefficient for any given trace where D is the partition coefficient for any given trace element between phases; D is a constant for dilute element between phases; D is a constant for dilute concentrations of elementsconcentrations of elementsFor dilute solutions can substitute D for KFor dilute solutions can substitute D for KDD::D =D =Where CWhere CSS = the concentration of some element in = the concentration of some element inthe solid phasethe solid phaseCCSSCCLL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 moremobile, particularly if a fluid phase is involvedmobile, particularly if a fluid phase is involvedHigh field strength (HFS) elementsHigh field strength (HFS) elementsSmaller, highly chargedSmaller, highly chargedLarge Ion Large Ion Lithophiles Lithophiles ((LILsLILs))Low field strength (large ions, Low field strength (large ions, lower charge), more mobilelower charge), more mobileTable 9-1. Partition Coefficients (CS/CL) for Some Commonly Used Trace Elements in Basaltic and Andesitic RocksOlivine 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 Ni14570.9550.016.8 29Cr 0.70 10 34 1.3450.012.00 7.4La 0.0070.030.056 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 estimatedRare Earth ElementsCompatibility 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