Special report : Mass spectrometry
Chemical and isotopic analysis of rocks by ion microprobe:
in situ characterization on the micrometric scale
 

n° 386 - September 2000

 


The ion microprobe is a mass spectrometry instrument that has been developed over the past 30 years and which analyses secondary ions emitted by a sample bombarded with a beam of primary ions. It enables high resolution in situ analysis to be carried out and has many applications in fields such as microelectronics, life sciences, medicine, and the earth and astronomical sciences.
In the earth sciences, this technique has been applied to high resolution study of complex samples either to assay trace elements in minerals or to determine the isotopic compositions of many elements.
Along with these analytical developments, ion microprobes dedicated to the earth sciences have been developed to produce high sensitivity at very high mass resolution. Examples of applications include:

  • in situ zircon dating, resulting in dating the oldest terrestrial minerals, which are more than 4 billion years old;
  • intra-crystalline isotopic heterogeneities, which have been observed in different minerals to probe their history and evolution;
  • the composition of mineral phases from deep in the earth, studied by examining vitreous and crystalline inclusions;
  • isotopic anomalies in refractory inclusions, studied to provide information regarding nucleosynthesis in different star types;
  • studies of the isotopic composition of the solar wind implanted in grains of lunar dust, which have provided a better comprehension of the function of the sun;
  • measuring the isotopic composition of hydrogen in meteorites to determine the origin of water in the protosolar nebula.

    The team at CNRS "Centre de recherches pétrographiques et géochimiques" (CRPG, Petrographic and Geochemical Research Centre), has been honing its skills with ion microprobes in the above fields since the mid 1980s, primarily by in situ dating, and measuring the isotopic composition of light elements applied to environmental or paleoenvironmental problems and cosmochemistry.



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