Helium solubility in olivine and implications for high He/He in ocean island basalts

• Published in: Nature (London) 2005-10, Vol.437 (7062), p.1140-1143
• Main Authors: Parman, Stephen W, Kurz, Mark D, Hart, Stanley R, Grove, Timothy L
• Format: Article
• Language: English
• ISSN: 0028-0836
• DOI: 10.1038/nature04215

High He/He ratios found in ocean island basalts are the main evidence for the existence of an undegassed mantle reservoir. However, models of helium isotope evolution depend critically on the chemical behaviour of helium during mantle melting. It is generally assumed that helium is strongly enriched in mantle melts relative to uranium and thorium, yet estimates of helium partitioning in mantle minerals have produced conflicting results. Here we present experimental measurements of helium solubility in olivine at atmospheric pressure. Natural and synthetic olivines were equilibrated with a 50% helium atmosphere and analysed by crushing in vacuo followed by melting, and yield a minimum olivine-melt partition coefficient of 0.0025 plus or minus 0.0005 (s.d.) and a maximum of 0.0060 plus or minus 0.0007 (s.d.). The results indicate that helium might be more compatible than uranium and thorium during mantle melting and that high He/He ratios can be preserved in depleted residues of melting. A depleted source for high He/He ocean island basalts would resolve the apparent discrepancy in the relative helium concentrations of ocean island and mid-ocean-ridge basalts.