–Sub-project 3 –
Establishing a world-class laboratory of isotope geochemistry


Isotope and trace element geochemistry plays a pivotal role in the development of modern earth sciences. In this subproject, a high-quality and high-performance laboratory has been being constructed to the success of the studies in the subprojects 1 and 2. We have designed infrastructure, set up preparation suites and geochemical clean rooms, and developed analytical methods of isotopic measurement and high precision trace metal determination.

 
1. Installation of ICPMS, stable Isotope MS and Laser Ablation device:

(a) One sector field ICPMS (SF-ICPMS), Thermo Electron ELEMENT II, was purchased and housed in room 105 of the Department of Geosciences.
(b) One multi-channel ICPMS (MC-ICPMS), Thermo Electron Neptune, was housed in the early summer, 2004.
(c) One stable isotope MS, Thermo Electron MAT 253, was installed in room 102B.
(d) One Laser Ablation device, New Wave UP213, was placed in room 105.

2. Micro-sampling clean room:

Three class-100 working benches, one micro-sampling device, and one 5-digit and one 7-digit electronic balances was housed in a class 10,000 micro-sampling room.
(a) Class-100 working benches are for subsampling of carbonates and hard rocks.
(b) A micro-sampling device, New Wave Micromill, is used to subsample fine powder. The spatial resolution is as good as 1 micrometer.
(c) Electronic balances are for weighing subsamples.

3. Geochemical clean room:

The original geochemical clean room with 4 working benches has been renovated with 8 more class-100 working benches, two hoods, and one pure water system. All chemistry for Sr, Nd, U-Th, Hf and Pb can be performed in the either original suite or the new space.

4. Development of analytical techniques:

We proposed to develop measurement of high precision isotopic compositions and concentrations in this subproject. As planned, five categories of analytical techniques will be established. They are (1) Sr, Nd, Pb and Hf isotopes on Finnigan Neptune, (2) U-Th isotopes on Finnigan Element II and Neptune, (3) Ca isotope analysis on Finnigan Neptune, (4) High precision trace metals in carbonates on Finnigan Element II, and (5) micro-domain analysis with laser ablation-ICPMS. The analytical techniques, which have been established, are Sr and Nd isotopes on Finnigan Neptune, U isotopic and concentration on Neptune, U-Th isotopes on Element II, and high precision trace metals in carbonates on Agilent 7500s. Other techniques are also in progress.
 

(a) Sr and Nd isotopes on Neptune: Long-term reproducibility is ± 40 ppm (2 sigma) for 87Sr/86Sr determination in standard NBS987 (Fig. 1) and ± 20 ppm (2 sigma) for 143Nd/144Nd in standard JNd-1 (Fig. 2).
 

 
 
 
 


Fig. 1 Duplicate measurement of NBS987 Sr standard on NTU MC-ICPMS, Neptune. The long-term external precision is ± 40 ppm (2 sigma).

 
     
 
 
 


Fig. 2 Duplicate measurement of JNdi-1 Nd standard on NTU MC-ICPMS, Neptune. Our method gives a long-term external precision of ± 20 ppm (2 sigma).

 
 

(b) U isotopic and concentration on Neptune: Duplicate measurement of NBL-112a U standard shows good precision and accuracy can be offered by our developed method. The external precision is ± 0.9 (2 sigma) (Fig. 3).

     
 
 
 


Fig. 3 Measurement of NBL-112a U standard on Neptune. Our method can offer a long-term external precision of ± 0.9.

 
     

(c) U-Th isotopes on Element II: The methodology of U-Th determination with permil-level precision has been set up (Fig. 4).

     
 
 
 


Fig. 4 Duplicate measurement of NBL-112a U standard on Element II. Our method can offer an analytical precision as good as 1-2 for U-Th isotopic determination.

 
     

(d) High precision trace metals in carbonates on Agilent 7500s. We have developed a high precision analytical technique of carbonate trace metal determination with cool-plasma inductively coupled plasma quadrupole mass spectrometry (ICP-QMS), which provides a within-run precision of 0.1-0.4% and a long-term reproducibility of 0.84% for Mg/Ca and 0.49% for Sr/Ca (Fig. 5).
 

     
 
 
 


Fig. 5 Replicate measurements made on standards and samples show long-term external uncertainties of Mg/Ca = 0.84% and Sr/Ca = 0.49% by Agilent 7500s with cool plasma technique.