Investigation of 129Xe and fission Xe in the terrestrial atmosphere and lithosphere: implications for the evolution of the Earth's atmosphere

Informazioni relative al progetto

ID dell’accordo di sovvenzione: INTAS-94-2397

Progetto chiuso

Data di avvio 1 Aprile 1995

Data di completamento 31 Marzo 1998

Finanziato da

• International Association for the promotion of cooperation with scientists from the independent states of the former Soviet Union (INTAS), 1993-

Costo totale € 0,00

Contributo UE € 49 700,00

Coordinato da

Max-Planck Gesellschaft zur Förderung der Wissenschaften e.V.
Germany

Risultati finali

Investigation of 129 Xe and fission Xe in the terrestrial atmosphere and lithosphere: implications for the evolution of the Earth's atmosphere

The isotopic composition of Xenon in he present Earth's atmosphere cannot be explained as a simple superposition of the common Xe reservoirs like AVCC, SUCOR, U-Xe, 129Xe and the β-decay product of primordial 129I, and fission Xe. Isotopic fractionation of Xe from these reservoirs also cannot be invoked to match the atmospheric Xe composition. Shukolyukov et al. (1994) proposed to add a new reservoir, Chemically Fractionated Fission Xe, CFF-Xe, to these new components. The aim of the project was to study the evidence of CFF-Xenon - the new terrestrial and extraterrestrial Xe component discovered by Shukolyukov et al. (1994) - by searching for its presence in selenides, tellurides, sulfides from "black smokers" of the oceanic floor, and in samples from uranium ore deposits, in order to understand the role CFF-Xe played for the composition of the Earth's atmosphere. To that end the noble gas mass-spectrometry facilities at the Vernadsky Institute of Geochemistry and Analytical Chemistry in Moscow were greatly improved. New pumping, gas extraction and gas purification systems were installed and new ion detection electronics developed, tested and implemented. With this modernised equipment Xe in tellurides (tellurobismuthites, telluric silver, and native tellurium), paragenous tellurides (telluric silver, petzite, altaite, and coloradoite), selenides (klaustalite and berzelianite), sulfides (stibnite and pyrites from "black smokers", Mid-Atlantic-Ridge), silicates from an uranium ore deposit (egyrine and albite), and andesite with high pressure fluid inclusions was analysed. For interpretation of the Xe data a new four-isotope diagram 131Xe/134Xe vs. 129Xe/132Xe was introduced to distinguish the various Xe-sources: atmospheric Xe, CFF-Xe, 235U- and 238U-fission Xe. In addition, the composition of CFF-Xe produced by the decay of the precursor elements I, Te and Sb was calculated: 131Xe/134Xe=20.17, 0.635, 9.13; 129Xe/132Xe=0.0001, 79.66, 2.40, respectively. The in depth interpretation of the measured Xe data is still in progress. However, already proposed is a mechanism for the formation of the Xe isotopic composition of the atmosphere in hydrothermal processes and for its subsequent migration into the atmosphere through the ocean. In this new model the atmosphere is not the primary source of Xe in the ocean. Only deep-seated hydrothermal systems could be. Hence it follows that in the case of uranium mineralisation the atmosphere is not the second end-member of mixing with Usf. Instead, the end member is a mixture of the typical Xe of the hydrothermal fluid that in turn is produced by mixing mantle Xe, CFF-Xe, and radiogenic Xe.