new frontiers in stable isotope geosciencecrcleme.org.au/pubs/monographs/mxtc2008/session...
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New Frontiers in Stable Isotope Geoscience (in South
Australia)Galen P. Halverson
Geology & Geophysics, School of Earth & Environmental Sciences The University of Adelaide
AcknowledgmentsARC-LIEF (2007)
CSIRO
Mike McLaughlin
Jason Kirby
John Foden
Current and potential capability in stable isotope geochemistry at UA
•Light stable isotopes (C, N, O, S) by
conventional gas source mass spectrometry
•Non-traditional isotope systems via MC ICP-MS
•Fe, Zn, Cu
•Other methods
Our Current Stable Isotope Facilities
Fisons Optima with an ISOCARB and Elemental Analyzer for analyses by Dual Inlet (DI) or Continuous Flow
(CF)
EA (CF)EA (CF)
SulphidesBarite
δ34S
EA (CF)Organicsδ15N
Isocarb (DI)Carbonateδ18O
Isocarb (DI)EA (CF)
CarbonateOrganics
δ13C
MethodMaterialIsotope ratio
Current Capability
Future Capability?
•δ18O on sulphates and organics (TC/EA)
•Simultaneous δ13C and δ18O on tooth enamel
•Simultaneous δ13C and δ15N measurements on
organics
Ultra-Trace Element and Isotope Analysis Laboratory (Waite
Campus)
The Finnigan Neptune High-Resolution Multi-Collector (MC
ICP-MS)
New Wave 193 nm Excimer Laser
Analysis by MC ICP-MS
Advantages•High precision
•High sample throughput
•Rapid switching between elements
Sample introduction via•Solution
•Laser Ablation
Stable isotope fractionation is a function of relative mass difference
between isotopes
Johnson et al., 2004
Likely stable isotope methods to be developed in
the early days:Fe, Zn, Cu, Mo
Other likely methods to be developed:
Fe, Zn, Cu, Mo
Likely stable isotope methods to be developed in
the early days:
Mg, Si, Se, Hg …
QuickTime™ and aTIFF (Uncompressed) decompressor
are needed to see this picture.
Analysis on a Neptune MC ICP-MS
Isobaric Interferences:
54Fe: 40Ar14N56Fe: 40Ar16O
57Fe: 40Ar16O1H58Fe: 40Ar18O54Fe: 54Cr58Fe: 58Ni
Analyses by high resolution MC-ICP-MS
M/ΔM = ~9000-11000Plateau: 180-220 ppm
To correct for internal mass fractionation:
Use a standard-sample-standard bracketing
±Ni/Zn/Cu doping
Analytical uncertainty of ~0.02‰/amu
Measuring multiple isotope ratios to monitor for untoward mass biases and interferences
y = 0.6774x + 0.0033
R2 = 0.9999
y = 0.6754x - 0.0004
R2 = 0.9997-1.0
-0.5
0.0
0.5
1.0
1.5
2.0
2.5
-1.0 0.0 1.0 2.0 3.0 4.0δ57Fe (‰ vs. IRMM-14)
6 M HCl leachBulk dissolution
Expression of isotopic ratios:
δ57FeIRMM-14 (‰) =57Fesamp54Fesamp
57FeIRMM-1454FeIRMM-14
- 1( 1000
δ57FeIRMM-14= 3/2(δ56FeIGN + 0.09)
Geochemical applications of iron isotopes:Igneous Petrology
Planetary Geology
As a biosignature?
Mn-Fe crusts and other seawater precipitates
Iron cycling in soils and groundwater
Iron cycling in sediments; origin of BIFs
0 1 2 3 4 5-1
redoxtransformations
redoxtransformations
Δ57Fe (‰)
Δ57Fe (‰)
Fe(II)aq - Fe(III)aq
Fe(III)aq - Hematite
0 1 2 3 4 5-1
Fe(II)aq - FeS
Fe(II)aq - Fe(III) (oxy)hydroxide
-2-3-4-5
Fe(II)aq - Hematite
Fe(II)aq - FeCO3
Fe(II)aq - Fe(II)adsorbed
-3-4-5 -2
Fe(III) (oxy)hydroxide - Fe(II)aq (DIR)Fe(II)aq - Magnetite
Fe(II)aq - FeCO3
Fe(II)aq - Fe(III)-(hydr)oxideFe(II)aq - Ca0.15Fe0.85CO3
Experimentally determined fractionations
Natural variationsin δ57Fe
Beard & Johnson (2004)
Mantle and terrestrial igneous rocks cluster around 0‰
Large variation in chemical precipitates and black shales
Beard & Johnson (2004)
→ Departures from 0‰ reflect redoxprocessing on the earth’s surface.
Beard & Johnson (2004)
Iron isotope data on Precambrian sediments
(Johnson et al., 2008)
Application of iron isotopes to Neoproterozoic syn-glacial iron-
formationRapitan Group BIF in northwestern Canada
Zn isotopes: 64Zn, 66Zn, 67Zn, 68Zn, 70Zn
δ66Zn(‰): 66Zn/64Zn vs. JMC 3-0749L
Natural variations: (-1‰< δ66Zn <1.3‰)
Applications:
•Seawater composition and evolution (bioproductivity)
(Carbonates; Manganese nodules)
•Zn ores
•Tracing Zn sources
•Biological uptake
•Soil processing
δ66Zn variation in deep sea carbonates over the past 180,000 years (Pichat et al., 2003)
Natural variationsin δ66Zn in geological materials.
Wilkinson et al. (2005)
δ66Zn variations in different parts of the Irish Midlands hydrothermal sphalerite ore system
Wilkinson et al.
Negative fractionation during incorporation of Zn into sphalerite?
Wilkinson et al.
Plants may generate large Zn fractionations:
Enrichment during Zn adsorption
Progressive depletion from roots to leaves (Weiss et al., 2005)
Viers et al. (2007)
Cu isotope fractionation:
• Large fractionation due to multiple oxidation states of Cu
• 3‰ fractionation associated with oxidation of Cu-sulphides (at surface temperatures)
• -3 to -4‰ fractionation associated with reduction of aqueous Cu(II) to Cu(I)
• Positive fractionation during Cu absorption (e.g. onto iron oxyhydroxides)
Cu isotopes: 63Cu, 65Cu
δ65Cu(‰): 65Cu/63Cu vs. SRM 976
Large fractionations:-3‰< δ65Cu <2.5‰
Applications:
•Cu ores•Biological uptake•Soil processing
Natural variations in Cu Isotopes
Ehrlich et al. (2004)
Distribution in δ65Cu in hydrothermal and weathered ore deposits
Larson et al.
Cu isotope fractionation:
•Large fractionation due to multiple oxidation states of Cu•Significant enrichment (3‰) associated with oxidation of Cu-sulphides (at surface temperatures)•Significant depletion (-3 to -4‰) associated with reduction of aqueous Cu(II) to Cu(I)•Positive fractionation during Cu adsorption (e.g. onto iron oxyhydroxides)
Iron isotopes via in situ LA-MC ICP-MS:
•Better than 0.35‰/amu precision
•Matrix-matched bracketing standard not necessary
•Variety of Fe phases (Fe-sulphides, hematite, goethite, siderite)
Other/future applications
•In situ Lu-Hf (e.g. zircons)•In situ Sr isotopes•Pb isotopes•Mo isotopes (palaeoredox)•Mg isotopes (weathering, dolomitisation)•Bo isotopes (in situ, solution)•U series dating (in situ, solution)
CONCLUSIONS:
•Non-traditional stable isotope geochemistry has huge potential in a broad range of applications
•Still in the early days (very little known about sources of fractionation)
•Will have the analytical facilities to make these measurements
CONCLUSIONS:
•Non-traditional stable isotope geochemistry has huge potential in a broad range of applications
•Still in the early days (very little known about sources of fractionation)
•Will have the analytical facilities to make these measurements
CAVEAT:
Need the people, resources, and scientific problems to realise the potential of stable isotope geochemistry in South Australia