new frontiers in stable isotope geosciencecrcleme.org.au/pubs/monographs/mxtc2008/session...

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