SHRIMP

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The SHRIMP (Sensitive High Resolution Ion Microprobe) is a large-diameter, double focusing secondary ion mass spectrometer (SIMS). The SHRIMP is primarily used for geological and geochemical applications. It can rapidly measure the isotopic and elemental abundances in minerals at a scale as small as 5 μm and is therefore particularly well-suited for the analysis of complex minerals, as often found in metamorphic terrains, some igneous rocks, and detrital minerals in sedimentary rocks. The most common application of the instrument is in U-Th-Pb geochronology, although the SHRIMP can be used to measure other isotopic and elemental abundances. The second generation instrument (SHRIMP II) is currently commercially produced by Australian Scientific Instrumentsin Canberra, in association with the Australian National University [1].

For U-Th-Pb geochronology a beam of primary ions (O2-) are mass analyzed, collimated and accelerated towards the target, and used to sputter “secondary” ions from the sample. These secondary ions are accelerated along the instrument where the various isotopes of uranium, lead and thorium are measured successively, along with reference peaks for Zr2O+, ThO+ and UO+. Since the sputtering yield differs between ion species and relative sputtering yield increases or decreases with time depending on the ion species (due to increasing crater depth, charging effects and other factors), the measured relative isotopic abundances do not relate to the real relative isotopic abundances in the target. Corrections are determined by analysing unknowns and standard material (matrix-matched material of known isotopic composition), and determining an analytical-session sepecific calibration factor[2].

[edit] SHRIMP Instruments around the World[3]

Instrument Number Institution Location SHRIMP model Year of commissioning
1 Australian National University Canberra I 1980
2 Australian National University Canberra II 1992
3 Curtin University of Technology Perth II 1993
4 Geological Survey of Canada Ottawa II 1995
5 Hiroshima University Hiroshima II 1996
6 Australian National University Canberra RG 1998
7 USGS & Stanford University Stanford RG 1998
8 National Institute of Polar Research Tokyo II 1999
9 Chinese Academy of Geological Sciences Beijing II 2001
10 All Russian Geological Research Institute St. Petersburg II 2003
11 Curtin University of Technology Perth II 2003
12 University of São Paulo São Paulo II tba
13 Chinese Academy of Geological Sciences Beijing IIe tba
14 Geoscience Australia Canberra IIe 2008
15 Korea Basic Science Institute Ochang IIe tba

[edit] References

  1. ^ Williams, I.S., 1998. U-Th-Pb geochronology by ion microprobe. In: M.A. McKibben, W.C. Shanks III and W.I. Ridley (Editors), Applications of microanalytical techniques to understanding mineralizing processes. Reviews in Economic Geology, pp. 1-35.
  2. ^ Claoué-Long, J., Compston, W., Roberts, J. and Fanning, C.M., 1995. Two Carboniferous ages: a comparison of SHRIMP zircon dating with conventional zircon ages and 40Ar/39Ar analysis. In: W.A. Berggren, D.V. Kent, M.-P. Aubry and J. Hardenbol (Editors), Geochronology, time scales and global stratigraphic correlation:. SEPM (Society for Sedimentary Petrology) Special Publication, pp. 3-21.
  3. ^ Stern, R., 2006. A time machine for Geoscience Australia. AusGeo News 81, 15-17.[1]

[edit] See also

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