Noble gas fluxes and mantle concentrations

The mantle fluxes that can be most easily identified are those of He. Also, concentrations in the mantle source regions from which He is lost through melting can be obtained where the source volume involved can be quantified. Estimated fluxes are given in Table 3. 

Ocean islands 38-670 0.04-0.73 Highest source He concentration estimate and range in magma generation rates 

Continental extension Stable continent 8.4-84 2.7 0.009-0.092 3.6 Magmatic component only Assuming steady state production and loss (Ballentine Bumard 2002, this volume) 

Upper mantle concentrations. Concentrations of He in mantle-derived MORE samples have clearly been subject to modifications and so are difficult to relate to the source. However, the concentration of He in the mantle can be determined by dividing the flux of He into the oceans by the rate of production of melt that is responsible for carrying this He from the mantle, which is equivalent to the rate of ocean crust production of 20 km /yr (Parsons 1981). Mid-ocean ridge basalts that degas quantitatively to produce a He flux of 1060 mol/yr must have an average He content of 

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