Submitted on September 4, 2007
Accepted on January 7, 2008
Rogue Mantle Helium and Neon
Francis Albarède 1*
1 UMR CNRS 5570, Ecole Normale Supérieure et Université de Lyon 1, 69007 Lyon, France.
* To whom correspondence should be addressed.
Francis Albarède , E-mail: albarede{at}ens-lyon.fr
The canonical model of He isotope geochemistry describes the lower mantle as undegassed but this view conflicts with evidence of recycled material in the source of ocean island basalts. Because mantle He is efficiently extracted by magmatic activity, it cannot remain in fertile mantle rocks for long periods of time. Here I suggest that helium with high 3He/4He ratios and neon rich in the solar component diffused early in the Earth’s history from low-melting point primordial material into residual refractory ‘reservoir’ rocks, such as dunites. The difference in 3He/4He ratios of ocean-island and mid-ocean ridge basalts and the preservation of solar neon are ascribed to the reservoir rocks being stretched and tapped to different extents during melting.
