1. G EOL 2312 I GNEOUS AND M ETAMORPHIC P ETROLOGY Lecture 7 Major, Minor and Trace Element Chemistry of Igneous Rocks February 8, 2016

2. Major elements : usually > 1 wt.% control properties of magmas major constituents of essential minerals Minor elements: usually 0.1 – 1 wt.% substitutes for major elements in essential minerals or may form small amounts of accessory mins. Trace elements : usually < 0.1 wt.% substitutes for major and minor elements in essential and accessory minerals 49.260.090.818850.62 2.0395.90.02121.31 16.1101.960.15799.76 2.72159.70.01701.05 7.7771.850.10816.69 0.1870.940.00250.16 6.4440.310.15989.88 10.556.080.187211.58 3.0161.980.04863.00 0.1494.20.00150.09 0.2370.980.00320.20 0.718.020.03882.40 0.9518.02 0.05273.26 99.971.6174100.00 W HOLE R OCK A NALYSIS OF A B ASALT Wt% Molecular Wt. Wt%/ Mol. Wt. Mole% SiO 2 TiO 2 Al 2 O 3 Fe 2 O 3 FeO MnO MgO CaO Na 2 O K2OK2O P2O5P2O5 H2O+H2O+ H2O-H2O- Ba5 Co32 Cr220 Ni87 Pb1.29 Rb1.14 Sr190 Th0.15 U0.16 V280 Zr160 La5.1 Trace Elements (ppm) structural water 1 wt.% = 10,000 ppm 1 ppm = 0.0001 wt.% adsorbed water

3. S PECTROSCOPIC A NALYTICAL T ECHNIQUES Whole Rock Analyses - X-ray Fluorescence (XRF) X-rays excite inner shell electrons producing secondary X-rays - Inductively Coupled Plasma (ICP) dissolved rock mixed with Ar gas is turned into plasma which excites atoms; generates X-rays - Instrumental Neutron Activation (INAA) nuclei bombarded with neutrons turning atoms radioactive; measure emitted X-rays - Mass Spectrometry(MS) atoms ionized and propelled through a curved electromagnet which seperates the ions by weight (good for isotope analysis) Mineral Chemical Analyses - Electron Microprobe (EM) incident electron beam generates X-rays which whose characteristic wavelengths are measured (WDS) - Energy Dispersive Spectrometry (EDS) incident electron beam generates X-rays which whose characteristic energies are measured; attached to UMD’s SEM - X-ray Diffractometry(XRD) Incident X-rays are diffracted by characteristic mineral structure

4. C HEMICAL A NALYSES OF C OMMON R OCK T YPES THAT A PPROXIMATE M AGMA C OMPOSITIONS Rock - PeridotiteBasaltAndesiteRhyolitePhonolite SiO242.2649.2057.9472.8256.19 TiO20.631.840.870.280.62 Al2O34.2315.7417.0213.2719.04 Fe2O33.613.793.271.482.79 FeO6.587.134.041.112.03 MnO0.410.200.140.060.17 MgO31.246.733.330.391.07 CaO5.059.476.791.142.72 Na2O0.492.913.483.557.79 K2O0.341.101.624.305.24 H2O+3.910.950.831.101.57 Total98.7599.0699.399.5099.23 Magma - UltramaficMaficIntermed. Felsic Alkalic

5. CIPW N ORMATIVE C ALCULATIONS Mode is the volume % of minerals observed Norm is the weight % of minerals calculated from whole rock geochemical analyses by distributing major elements among rock-forming minerals 1) 2) 3) 4) 5) 6) 7) 8) 9) 10) 11) 13) 12) 14) 15) Numbers show the order that mineral are figured. See Winter (2001) Appendix for instructions.

6. G EOCHEMICAL P LOTS Objective: to show the co-variation of elemental components that may give insight to magmatic processes such as- partial melting magma mixing country rock assimilation/contamination fractional crystallization (or crystallization differentiation) Types: bivariate (X-Y) triangular normalization plots (spider diagrams)

7. H ARKER V ARIATION D IAGRAMS Winter (2001) Figure 8-2. Harker variation diagram for 310 analyzed volcanic rocks from Crater Lake (Mt. Mazama), Oregon Cascades. Data compiled by Rick Conrey (personal communication). The “Daly” Gap Real or an artifact of the variation of SiO 2 concentration with differentiation Variation of major and minor oxide abundances vs. SiO 2 (thought to be and indication of the evolved character of a magmatic system) Primitive Evolved Liquid Lines of Descent

8. D IFFERENTIATION I NDEXES from Winter (2001)

9. M AGMA S ERIES M AGMA S ERIES R ELATED TO T ECTONIC P ROVINCES Na 2 O + K 2 O SiO 2 Sub- alkaline

10. S UBALKALINE D ISCRIMINATION D IAGRAMS AFM Diagram Tholeiitic--Calc-Alkaline boundary after Irvine and Baragar (1971). Can. J. Earth Sci., 8, 523-548 Na 2 O + K 2 O Fe 2 O 3 + FeO MgO

11. T ECTONIC P ROVINCE D ISCRIMINATION D IAGRAMS Rollinson (1993)

12. T ECTONIC P ROVINCE D ISCRIMINATION D IAGRAMS

13. T RACE E LEMENTS IN I GNEOUS P ROCESSES Transition Metals Rare Earth Elements Goldschmidt’s (1937) Rules of Element Affinity 1.Two ions with the same valence and radius should exchange easily and enter a solid solution in amounts equal to their overall proportions (e.g. Rb~K, Ni~Mg, Mn~Fe) 2.If two ions have a similar radius and the same valence: the smaller ion is preferentially incorporated into the solid over the liquid (e.g., Mg > Fe in Olivine - Ionic Field Strength (Charge/Radius) Alkalis Precious Metals Fe +2 156 A Mg +2 145 A

14. T RACE E LEMENT C OMPATIBILITY Compatibility – degree to which an element prefers to partition into the solid over the liquid phase. Kd (i) 1 – Mineral-Liquid Partition Coefficient for element i in mineral 1 Kd (i) 1 = C (i) mineral 1 / C (i) liquid (C (i) - concentration of element i in wt. %) Kd (i) 1 > 1 – Compatible, Kd (i) 1 < 1 – Incompatible D (i) – Bulk Rock Partition Coefficient for element i D (i) = x 1 Kd (i) 1 + x 2 Kd (i) 2 + x 3 Kd (i) 3 +.... (x 1 – proportion of mineral 1)

15. I NCOMPATABILITY OF T RACE E LEMENTS P ARTITION C OEFFICIENTS (C S /C L ) Compatible

16. B EHAVIOR OF T RACE E LEMENTS DURING P ARTIAL (B ATCH ) M ELTING C L /C o = 1/[D (i) (1-F) + F] F - Fraction of Liquid D (i) - Bulk Distribution Coefficient for Element i As D (i)  0 (strongly IE) C L /C o ≈ 1/F Normal Range of Partial Melting in the Mantle

17. Winter (2001) Figure 9-4. Rare Earth concentrations (normalized to chondrite) for melts produced at various values of F via melting of a hypothetical garnet lherzolite using the batch melting model (equation 9-5). Degree of Partial Melting (F) From Rollinson (1993) Compatible Incompatible B EHAVIOR OF R ARE E ARTH E LEMENTS DURING P ARTIAL (B ATCH ) M ELTING OF THE M ANTLE

18. B EHAVIOR OF T RACE E LEMENTS DURING F RACTIONAL C RYSTALLIZATION Rayleigh Distillation: C L /C o = F (D (i) -1) F - Fraction of Liquid Remaining D (i) - Bulk Distribution Coefficient for Element i From Rollinson (1993)

19. B EHAVIOR OF T RACE E LEMENTS DURING F RACTIONAL C RYSTALLIZATION From Rollinson (1993) Compatible Incompatible Bulk Rock Partition Coefficient of Ce,Yb, and Ni for Crystallization of: 1) Troctolite (70% Pl, 30% Ol) D (Ce) = x Pl Kd (Ce) Pl + x Ol Kd (Ce) Ol =.7*.103 +.3*.007 = 0.092 D (Yb) = x Pl Kd (Yb) Pl + x Ol Kd (Yb) Ol =.7*.07 +.3*.065 = 0.069 D (Ni) = x Pl Kd (Ni) Pl + x Ol Kd (Ni) Ol =.7*.01 +.3*25= 7.5 2) Olivine Gabbro (63% Pl, 12% Ol, 25% Cpx) D (Ce) = x Pl Kd (Ce) Pl + x Ol Kd (Ce) Ol + x Cpx Kd (Ce) Cpx =.63*.103 +.12*.007 +.25*.09 = 0.088 D (Yb) = x Pl Kd (Yb) Pl + x Ol Kd (Yb) Ol + x Cpx Kd (Yb) Cpx =.63*.07 +.12*.065 +.25*.09 = 0.074 D (Ni) = x Pl Kd (Ni) Pl + x Ol Kd (Ni) Ol + x Cpx Kd (Ni) Cpx =.63*.01 +.12*25 +.25*8 = 5

20. T RACE E LEMENT B EHAVIOR DURING F RACTIONAL C RYSTALLIZATION F (fraction of liquid remaining) Rayleigh Distillation: C L /C o = F (D-1) Conclusions: Fractional crystallization of mafic magmas gradually increases the concentrations of similarly incompatible elements, but has a minimal effect on their ratios; and strongly decreases the concentrations of compatible elements F (fraction of liquid remaining) C L /C o TroctoliteOlivine Gabbro

21. T RACE E LEMENT B EHAVIOR DURING F RACTIONAL C RYSTALLIZATION E XAMPLE F ROM THE S ONJU L AKE I NTRUSION E. Compatible Elements

22. R ARE E ARTH E LEMENT (REE)D IAGRAMS C OMPARES R ATIOS AND N ORMALIZES TO A S TANDARD C OMPOSITION Light REEHeavy REE From Rollinson (1993) Fractional crystallization increases the REE abundance, but has a neglible effect on the REE pattern REE commonly normalized to chondrite composition – thought to approximate the unfractionated composition of the earth. Fractional crystallization of olivine from a komatiitic melt

23. REE R ATIO D IAGRAMS S ORTING EFFECTS OF P ARTIAL MELTING VS. F RACTIONAL C RYSTALLIZATION From Rollinson (1993) Fractional Crystallization - minimal change in REE ratios Partial Melting - significant change in REE ratios

24. T RACE E LEMENT N ORMALIZATION P LOTS (S PIDER D IAGRAMS ) Most Least Incompatible Elements (likes magma) Compatible Elements (likes minerals) Rock/Standard Comp* Common Standard Compositions for Normalizing Chondritic meteorite Avg. Mid-ocean Ridge Basalt (MORB) Primitive Mantle Primitive Ocean Island Basalt (OIB) Enriched Depleted Negative Anomaly Positive Anomaly