Quick Search:    advanced search

GSW Home   GeoRef Home   My GSW Alerts   Contact GSW   About GSW   Journals List   Help

This Article Figures Only Full Text Full Text (PDF) Alert me when this article is cited Alert me if a correction is posted Services Email this article to a friend Similar articles in this journal Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via Web of Science (5) Citing Articles via Google Scholar Google Scholar Articles by HARRISON, D. Articles by TURNER, G. Search for Related Content GeoRef GeoRef Citation

Possible diffusive fractionation of helium isotopes in olivine and clinopyroxene phenocrysts

¹ Isotopengeologie, ETH Zentrum, Sonneggstrasse 5, CH-8092, Zurich, Switzerland, Corresponding author, e-mail: harrison{at}erdw.ethz.ch
² Cardiff University (BAS/NIGL), Cardiff CF1 3YE, UK
³ Department of Earth Sciences, University of Manchester, Oxford Road, Manchester M13 9PL, UK

New helium isotope data (³He/⁴He) from a series of co-genetic Siberian lavas of Cenozoic age (0.6 - 3 Ma) provide possible evidence for mass-dependent helium isotope fractionation. These lavas, erupted around the Baikal rift, have sampled subcontinental lithospheric mantle (SCLM). ³He/⁴He ratios measured in clinopyroxene and olivine phenocrysts are between 0.9 - 8.3 R_a. The SCLM in this region is therefore characterised by the higher unmodified ³He/⁴He ratios, which are similar to the source region of mid-ocean ridge basalts (MORB). Helium isotope variation of this scale and order within local regional volcanic settings has previously been ascribed to purely, crustal contamination or radiogenic ingrowth of ⁴He. However, we argue that helium isotopes may also be affected by mass-dependent fractionation. This can occur during helium diffusion from the phenocrysts within sub-solidus magmas.

Key-words: helium isotopes, mass fractionation, diffusion, sub-continental lithospheric mantle.