Abstract
Abstract: Noble gases are very rare elements in most relevant samples in geochemistry and cosmochemistry. Noble gases may perhaps also look rather boring to chemists, as they do not form any stable compounds. However, it is just their rarity and chemical inertness which makes noble gases versatile elements in a very wide range of fields, such as oceanography, climatology, environmental sciences, meteorite studies, rock dating, early solar system and early Earth history, and many others. Mass spectrometry is by far the main analytical tool in noble gas geochemistry and cosmochemistry, partly because the rarity of noble gases often allows researchers to recognize in the same sample different noble gas "components" of different origin and hence different isotopic composition. This contribution attempts to illustrate the wide range of applications of noble gas mass spectrometry in the Earth sciences with selected examples.
Highlights
Dating by the 39Ar–40Ar and I-Xe MethodsThe by far best-known application of noble gas mass spectrometry is dating by the K-Ar method,[16] one of the first isotope-based rock dating techniques
Noble gases are very rare elements in most relevant samples in geochemistry and cosmochemistry
Many details about the sources of Earth’s noble gases remain unclear, but the big picture is that the Earth’s mantle retains He and Ne broadly resembling in its isotopic composition the He and Ne in the Sun, whereas the Kr and the Xe in the mantle is similar to Kr and Xe in primitive meteorites.[57–59]
Summary
The by far best-known application of noble gas mass spectrometry is dating by the K-Ar method,[16] one of the first isotope-based rock dating techniques. Monitor samples of known age are irradiated next to the samples of interest This allows to determine parent and daughter concentrations with noble gas analyses alone. An even more important advantage is that the technique allows to recognize partial losses of the radiogenic isotope 40Ar by extracting the gas in several steps at increasing sample tem-. Radioactive 129I with a half-live of 15.7 Ma was present in the early solar system as a product of nucleosynthesis in heavy stars near the end of their lives It decayed into 129Xe within the first approx. The iodine-xenon system is primarily a relative chronometer, ‘only’ yielding age differences between events that happened in the first few ten Ma years of solar system history. We will see that the radiogenic fraction of 129Xe in the Earth is of interest to study acquisition and loss processes of the terrestrial atmosphere and mantle
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