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O-H_Stable_Isotopes - Earth Sciences 6510 H and O Isotopes...

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Earth Sciences 6510 H and O Isotopes and Applications Stephen J. Piercey Department of Earth Sciences Memorial University St. John’s, NL, Canada A1B 3X5 [email protected] Wednesday, 15 August, 12
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Outline Stable Isotopes: Definitions Isotopic fractionation and theoretical nomenclature. O and H isotopes, fluid-rock interaction, solvent tracing, and applications. C and S isotopes, solute (source) tracing, and applications. Stable isotope geothermometry. Wednesday, 15 August, 12
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Stable Isotopes Isotopes that have different isotopes but do not undergo radiogenic decay are referred to as stable isotopes. Stable isotopes tend to fractionate from each other rather than decay like radiogenic isotopes. Fractionation can occur either by: Equilibrium Fractionation (i.e., evaporation, mineral- crystal) Kinetic Fractionation (i.e., biogenic fractionation – metabolism). Wednesday, 15 August, 12
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Light Stable Isotopes (note S just above diagram) From Wilton (2010) Wednesday, 15 August, 12
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Light Stable Isotopes Element Natural Isotopes Natural Abundances Ratio Measured Reference Standard* Hydrogen 1 H 2 D 99.9844% 0.0156% D/H V-SMOW Boron 10 B 11 B 98.988% 1.02% 11 B/ 10 B None Carbon 12 C 13 C 98.89% 1.11% 13 C/ 12 C PDB Nitrogen 14 N 15 N 99.64% 0.36% 15 N/ 14 N ATM Oxygen 16 O 17 O 18 O 99.763% 0.0375% 0.1995% 18 O/ 16 O V-SMOW Sulphur 32 S 33 S 34 S 36 S 95.02% 0.75% 4.21% 0.02% 34 S/ 32 S CDT ATM = atmosphere, CDT = Canon Diablo troilite, PDB = Pedee Formation belemnite, V-SMOW = Vienna standard mean ocean water Wednesday, 15 August, 12
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Wednesday, 15 August, 12
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Information from Stable Isotopes Composition and source of fluids and solutes Temperature of deposition Physicochemical conditions or mechanisms of mineral precipitation Ore-related alteration signatures Fluid flow paths Exploration vectors These phenomena are based on the fractionation of stable isotopes from one another Wednesday, 15 August, 12
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Stable Isotope Fractionation Isotopic Exchange Reactions (Equilibrium Fractionation) ½ Si 16 O 2 + H 2 18 O = ½ Si 18 O 2 + H 2 16 O Zn 32 S + Pb 34 S = Zn 34 S + Pb 32 S Wednesday, 15 August, 12
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Stable Isotope Fractionation Degree = f( Δ mass , temperature) Significant for light stable isotopes 2 D vs. 1 H 13 C vs. 12 C 15 N vs. 14 N 18 O vs. 16 O 34 S vs. 32 S Insignificant for heavy radiogenic isotopes (e.g., 87 Sr vs. 86 Sr, 143 Nd vs. 144 Nd, 187 Os vs. 188 Os, 208 Pb vs. 207 Pb vs. 206 Pb) Wednesday, 15 August, 12
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easier to measure ratios and easier to interpret differences , so values expressed as a relative difference function: where R x = ratio of heavy (rare) to light (abundant) isotope of element x expressed in parts per thousand or permil (‰) +ve values are isotopically heavier than standard, -ve values are isotopically lighter than standard Delta Function, δ δ x = 10 3 R x R std R std R std Λ Ν Μ Ξ Π Ο = 10 3 R x R std R std Λ Ν Μ Ξ Π Ο = 10 3 R x R std 1 Λ Ν Μ Ξ Π Ο Wednesday, 15 August, 12
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Standards for Stable Isotopes Measure isotope ratios on GCMS or SIMS using appropriate standards Standards Element Standard
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