Helium isotopic evidence for a lower mantle component in depleted Archean Komatiite

Science

Volumn 273, Issue 5271, 1996, Pages 93-95

  Richard, Denis ^a,b   Marty, Bernard ^a,b   Chaussidon, Marc ^a,b   Arndt, Nicholas ^c  

^a CNRS   (France)

^b UNIVERSITÉ DE LORRAINE   (France)

^c UNIVERSITÉ DE RENNES 1   (France)

Author keywords

[No Author keywords available]

Indexed keywords

HELIUM; ISOTOPE;

ARTICLE; CHEMICAL ANALYSIS; GEOGRAPHIC DISTRIBUTION; GEOLOGY; HIGH TEMPERATURE; PRIORITY JOURNAL;

ARCHAEAN; HELIUM ISOTOPE; KOMATIITE; MANTLE COMPONENT;

EID: 0029663545     PISSN: 00368075     EISSN: None     Source Type: Journal    
DOI: 10.1126/science.273.5271.93     Document Type: Article

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28. 15 mol.
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31. 9 years old, and assimilation of this crust is reflected in radiogenic Pb isotope compositions [B. Dupré and N. T. Arndt, Chem. Geol. B5, 35 (1990); C. Chauvel, B. Dupré, N. T. Arndt, in The Geology of the Belingwe Greenstone Belt, Zimbabwe, M. J. Bickle and E. G. Nisbet, Eds. (Balkema, Rotterdam, 1993), pp. 167-174]. This would suggest that He, like Pb, is a more sensitive indicator of crustal contamination than the more compatible Nd. In the Ottawa Island komatiite, the case for contamination is very sound. Evidence is found not only in the trace-element ratios and Nd and Pb isotopic compositions but also as a result of an examination of thin sections, which reveals arrays of micrometer-sized fluid inclusions that are likely to be secondary and may represent remnants of secondary fluid circulation.
32. 3He extracted from the Alexo olivines (Table 1) could have been produced by radioactivity.
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37. a cannot be characteristic of the upper mantle.
38. a cannot be characteristic of the upper mantle.
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40. We thank A. M. Boullier for advice during fluid and melt inclusion characterization, J. C. Demange for the care and rapidity with which he set up the mass spectrometer, and X. Framboisier who provided assistance during the analysis. This work benefited from discussions with J. Ludden and M. Ozima and from internal review by I. N. Tolstikhin. This is Centre de Recherches Pétrographiques et GénchimiquesCNRS contribution 1200.