A statistical test of the two reservoir model for helium isotopes

A common hypothesis is that helium isotopes in mantle-derived materials represent two distinct populations, the midocean ridge (MORB) reservoir and the oceanic island (OIB) reservoir. We ask the question ‘Can we disprove the null hypothesis that OIB and MORB samples are drawn from the same population distribution function?’ The answer is no, meaning that the datasets could be drawn from the same population. Previous studies have reached the opposite conclusion by comparing extreme values in one population with the mean value, or range, of the other population after the extreme values are removed. The variance of the 3He/4He distribution for various ridge segments decreases with the spreading rate and the high variance of individual OIB datasets is consistent with slow spreading, small sampled volume, or low degrees of melting or degassing.